presentation on the working of bpf and brf

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Characteristics of an Ideal Filter (LPF, HPF, BPF and BRF)

What is a filter.

A filter is a frequency selective network, i.e., it allows the transmission of signals of certain frequencies with no attenuation or with very little attenuation and it rejects all other frequency components.

What is an Ideal Filter?

An ideal filter is a frequency selective network that has very sharp cut-off characteristics, i.e., it transmits the signals of certain specified band of frequencies exactly and totally rejects the signals of frequencies outside this band. Therefore, the phase spectrum of an ideal filter is linear.

Ideal Filter Characteristics

Based on the frequency response characteristics, the ideal filters can be of following types −

Ideal Low-Pass Filter (LPF)

Ideal High-Pass Filter (HPF)

Ideal Band-Pass Filter (BPF)

Ideal Band-Reject Filter (BRF)

Ideal All Pass Filter

Ideal low pass filter (lpf).

An ideal low pass filter is the one which transmits all the signal of frequencies less than a certain frequency $\mathit{\omega_{c}}$ radians per second without any distortion and blocks all the signals of frequencies above $\mathit{\omega_{c}}$ radians per second. Where, the frequency $\mathit{\omega_{c}}$ radians per second is called the cut-off frequency . The phase function of an ideal low-pass filter is given by $[\mathit{\theta \left(\omega\right)=-\omega t_{d}}]$.

The transfer function of an ideal low-pass filter is given by,

$$\mathrm{\mathit{\left | H\left(\omega\right) \right |=\left\{\begin{matrix} \mathrm{1}\:\:\mathrm{for}\:\left | \omega\ \right|<\omega_{c} \ \mathrm{2} \:\:\mathrm{for}\:\left | \omega\ \right|>\omega_{c} \end{matrix}\right.}}$$

Therefore, the frequency response characteristics of an ideal low-pass filter is a gate or rectangular function and it is shown in Figure-1.

Ideal High Pass Filter (HPF)

An ideal high pass filter transmits all the signals of frequencies above a certain frequency $\mathit{\omega_{c}}$ radians per second without any distortion and blocks completely all the signals of frequencies below the frequency $\mathit{\omega_{c}}$ radians per second. Here, the frequency $\mathit{\omega_{c}}$ radians per second is called the cut-off frequency . The phase function of an ideal high pass filter is given by,

$$\mathrm{\theta (\omega )=-\omega t_{d}}$$

The transfer function of an ideal high pass filter is given by,

$$\mathrm{\mathit{\left | H\left(\omega\right) \right |=\left\{\begin{matrix} \mathrm{0}\:\:\mathrm{for}\:\left | \omega\ \right|<\omega_{c} \ \mathrm{1} \:\:\mathrm{for}\:\left | \omega\ \right|>\omega_{c} \end{matrix}\right.}}$$

Figure-2 shows the frequency response characteristics of an ideal high pass filter.

Ideal Band Pass Filter (BPF)

An ideal band pass filter transmits all the signals of frequencies within a certain frequency band $\mathit{\left(\omega _{\mathrm{2}}-\omega_{\mathrm{1}}\right)}$ radians per second without any distortion and completely blocks all the signals of frequencies outside this frequency band.

The frequency band $\mathit{\left(\omega _{\mathrm{2}}-\omega_{\mathrm{1}}\right)}$ is called the bandwidth of the band-pass filter.

The phase function of an ideal band-pass filter for the distortion less transmission is given by,

$$\mathrm{\mathit{\theta\left(\omega\right)=-\omega t_{d}}}$$

And the transfer function of an ideal band-pass filter is given by,

$$\mathrm{\mathit{\left | H\left(\omega\right) \right |=\left\{\begin{matrix} \mathrm{1}\:\:\mathrm{for}\:\left | \omega_{\mathrm{1}}\ \right|<\omega< \left | \omega_{2}\ \right| \\mathrm{0} \:\:\mathrm{for}\:\omega<\left | \omega_{\mathrm{1}}\ \right|\&\:\omega>\left | \omega_{\mathrm{2}}\ \right| \end{matrix}\right.}}$$

The figure-3 shows the frequency response characteristics of an ideal band-pass filter (BPF).

Ideal Band Rejection Filter (BRF)

An ideal band rejection filter rejects completely all the signals of frequencies within a frequency band $\mathit{\left(\omega _{\mathrm{2}}-\omega_{\mathrm{1}}\right)}$ radians per second and transmits all the signals of frequencies outside the frequency band without any distortion.

In this case, the frequency band $\mathit{\left(\omega _{\mathrm{2}}-\omega_{\mathrm{1}}\right)}$ is called the rejection band. The Band rejection filter is also called the band stop filter (BSF) or band-elimination filter (BEF). The phase function of an ideal band rejection filter is $\mathit{\theta\left(\omega\right)=-\omega t_{d}}$.

And the transfer function of an ideal band rejection filter is given by,

$$\mathrm{\mathit{\left | H\left(\omega\right) \right |=\left\{\begin{matrix} \mathrm{0}\:\:\mathrm{for}\:\left | \omega_{\mathrm{1}}\ \right|<\omega< \left | \omega_{\mathrm{2}}\ \right| \\mathrm{1} \:\:\mathrm{for}\:\omega<\left | \omega_{\mathrm{1}}\ \right|\&\:\omega>\left | \omega_{\mathrm{2}}\ \right| \end{matrix}\right.}}$$

The figure-4 shows the frequency response characteristics of an ideal band rejection filter.

An all pass filter is a frequency selective network which transmits signals of all the frequencies without any distortion. That is, the bandwidth of an all pass filter is infinite as shown in figure-5. The transfer function of an ideal all pass filter is given by,

$$\mathrm{\mathit{\left| H\left(\omega\right)\right |=\left\{\mathrm{1}\:\:\mathrm{for} \:\mathrm{all}\:\omega\right.}}$$

And the phase function of an ideal all pass filter for the distortion less transmission is $\mathit{\theta\left(\omega\right)=-\omega t_{d}}$.

Note - All ideal filters are non-causal systems. Therefore, none of them can be physically realizable.

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Band Reject Filter Circuit:

In this Band Reject Filter Circuit, frequencies are attenuated in the stop band and passed outside it, as shown in Fig. 15.20(b). As with band pass filters, band reject filters can also be classified as (i) wide and (ii) narrow band.

The narrow band reject filter circuit is also called the notch filter . Because of its higher Q which is greater than 10, the bandwidth of the narrow band reject filter is much smaller than that of the wide band reject filter. The band reject filter is also called a band stop or band elimination filter because it eliminates a certain band of frequencies.

Wide Band Reject Filter:

Figure 15.20 (a) shows wide band reject filter circuit using a low pass filter, a high pass filter and a summing amplifier. For a proper band reject response, the low cutoff frequency f L of the high pass filter must be larger than the high cutoff frequency f H of the low pass filter. Also, the pass band gain of both high pass and low pass sections must be equal.

Narrow Band Reject Filter:

The narrow band reject filter, often called the notch filter, is commonly used for the attenuation of a single frequency. For example, it may be necessary to attenuate 60 Hz or 400 Hz noise or hum signals in a circuit. The most com­monly used notch filter is the Twin T network, shown in Fig. 15.21(a), which is a passive filter composed of two T shaped networks.

One T network is made up of two resistors and a capacitor , while the other is made of two capacitors and a resistor. The frequency at which maximum attenuation occurs is called the notch-out frequency, given by

One disadvantage of the passive twin T network is that it has a relatively low figure of merit, Q. As discussed earlier, the higher the value of Q, the more selective is the filter. Therefore, to increase the Q of the twin T network sig­nificantly, it should be used with a voltage follower, as shown in Fig. 15.21(b). Figure 15.21(c) shows the frequency response of a notch filter.

The Notch filters are used in communications, biomedical instruments, etc. where the elimination of certain frequencies is necessary.

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LPF vs HPF vs BPF vs BSF-Difference between LPF,HPF,BPF,BSF filter types

This page on LPF vs HPF vs BPF vs BSF describes difference between LPF,HPF,BPF and BSF filter types. These are all filters used in communication chain for various functions. Based on where they have been placed they are mainly of two types viz. analog and digital. The filters which operate on digital data is referred as digital filter and one which operates on analog data is referred as analog filter. We will see basic difference between basic filter types.

The short form of Low Pass Filter is LPF . This filter passes the lower range of frequencies and stops or filter out higher range of frequencies. As shown LPF passes frequencies from 0 to Fc and stops all the frequencies above Fc.

The short form of High Pass Filter is HPF . This filter passes the higher frequencies and stops or filter out lower frequencies. As shown HPF passes frequencies from Fc and above and stops frequencies from 0 to Fc.

The short form of Band Pass Filter is BPF . This filter passes band of frequencies. As shown the BPF passes frequencies between F1 and F2. It rejects frequencies from 0 to F1 and also any frequencies from F2 and above.

The short form of Band Stop Filter is BSF . This filter stops band of frequencies from F1 to F2 and passes frequencies from 0 to F1 as well as from F2 and above.

Filter RELATED LINKS

analog vs Digital Filter FIR vs IIR filter Low Pass FIR filter MATLAB implementation Analog LPF vs HPF MATLAB source code

What is Difference between

FIR filter Vs. IIR filter difference between FDM and OFDM Difference between SC-FDMA and OFDM Difference between SISO and MIMO Difference between TDD and FDD Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n OFDM vs OFDMA CDMA vs GSM Bluetooth vs zigbee

RF and Wireless Terminologies

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IIR Filters FIR vs. IIR IIR filter design procedure

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A review of progress about birefringent filter design and application in ti:sapphire laser.

1. Introduction

2. research progress of brf design, 2.1. tuning characteristics of single-plate brf, 2.2. tuning characteristics of multi-plate brf, 3. design of brf for single-frequency ti:sapphire tunable laser, 4. automatic control of brf used in single-frequency ti:sapphire tunable laser, 5. new application of birefringent tuning characteristic, 6. conclusions, author contributions, institutional review board statement, informed consent statement, data availability statement, conflicts of interest.

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Wei, J.; Su, J.; Lu, H.; Peng, K. A Review of Progress about Birefringent Filter Design and Application in Ti:sapphire Laser. Photonics 2023 , 10 , 1217. https://doi.org/10.3390/photonics10111217

Wei J, Su J, Lu H, Peng K. A Review of Progress about Birefringent Filter Design and Application in Ti:sapphire Laser. Photonics . 2023; 10(11):1217. https://doi.org/10.3390/photonics10111217

Wei, Jiao, Jing Su, Huadong Lu, and Kunchi Peng. 2023. "A Review of Progress about Birefringent Filter Design and Application in Ti:sapphire Laser" Photonics 10, no. 11: 1217. https://doi.org/10.3390/photonics10111217

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What Is the Bilateral Filter Category: LPF, HPF, BPF or BSF?

I`m reading about Bilateral filter with images, I knew that it uses Gaussian filter (which is a LPF) as a domain filter plus a range filter and it is used to preserve edges(high freq component).

Can we consider Bilateral filter as a LPF ? .

I searched some articles: 1- Which approach is better for decomposing a image into high frequency and low frequency component?

The answer was that bilateral filter attenuates ""medium frequency "

2- How to Extract High Frequency and Low Frequency Component Using Bilateral Filter?

The answer was to consider bilateral filter as a LPF.

• image-processing
• edge-preserving-filter

• $\begingroup$ I posted and an answer. I think the main thing here is to think in the Patch Level. $\endgroup$ –  Royi Commented Oct 5, 2019 at 0:25

3 Answers 3

Neither. To me, filter classes using the notion of frequency bands (low-pass, high-pass, etc.) can be used safely in the linear case. And the bilateral filter is nonlinear. Edges are not really high-frequency: they often have sharp variations across the edge, but slow variation along it. Hence linear directional filters often have a derivative part and and orthogonal smoothing part.

I would consider the bilateral filter as an edge-preserving smoother , a broad and somewhat imprecise class.

Suggested reading: Fast and Provably Accurate Bilateral Filtering , 2016

The bilateral filter is a non-linear filter that uses a range filter along with a spatial filter to perform edge-preserving smoothing of images. A direct computation of the bilateral filter requires O(S) operations per pixel, where S is the size of the support of the spatial filter. In this paper, we present a fast and provably accurate algorithm for approximating the bilateral filter when the range kernel is Gaussian. In particular, for box and Gaussian spatial filters, the proposed algorithm can cut down the complexity to O(1) per pixel for any arbitrary S. The algorithm has a simple implementation involving N+1 spatial filterings, where N is the approximation order. We give a detailed analysis of the filtering accuracy that can be achieved by the proposed approximation in relation to the target bilateral filter. This allows us to estimate the order N required to obtain a given accuracy. We also present comprehensive numerical results to demonstrate that the proposed algorithm is competitive with the state-of-the-art methods in terms of speed and accuracy.

• $\begingroup$ What about the Patch Level? Have a look on my analysis. $\endgroup$ –  Royi Commented Oct 17, 2019 at 11:27

Bilateral Filter is indeed an Edge Preserving Filter. Moreover, due to being Spatially Variant Non Linear Filter it can not be applied using Fourier Transform. Since it has no representation in the Frequency Domain, it is not well defined how to classify it into one of the categories: LPF, HPF, BPF or BSF.

Nonetheless, let's try doing some analysis based on analyzing the filter itself and some empirical analysis. If we look at the filter per patch defined by the radius of the filter, we have fixed weights and we can analyze its effect.

Analysis of the Bilateral Filter Formula

The Bilateral Filter is given by:

$$ O \left( i, j \right) = \frac{1}{ {W}_{i, j} } \sum_{m = -r}^{r} \sum_{n = -r}^{r} w \left( i - m, j - n \right) I \left( i - m, j - n \right) $$

• $ O \left( i, j \right) $ - Output image value at pixel $ \left( i, j \right) $ .
• $ I \left( i - m, j - n \right) $ - Input image value at pixel $ \left( i - m, j - n \right) $ .
• $ r $ - Radius parameter of the filter.
• $ w \left( i - m, j - n \right) $ - Weight of the pixel $ \left( i - m, j - n \right) $ given by $ w \left( i - m, j - n \right) = {w}_{s} \left( i - m, j - n \right) {w}_{r} \left( i - m, j - n \right) = \exp \left( - \frac{ { \left( i - m \right) }^{2} + { \left( j - m \right) }^{2} }{ 2 {\sigma}_{s}^{2} } \right) \exp \left( - \frac{ { \left( I \left( i, j \right) - I \left( m, n \right) \right) }^{2} }{ 2 {\sigma}_{r}^{2} } \right) $ .
• $ {W}_{i, j} $ - Normalization factor of the pixel $ \left( i, j \right) $ given by $ \sum_{m = -r}^{r} \sum_{n = -r}^{r} w \left( i - m, j - n \right) $ .

So we have the Spatial Weight, which is just classic Gaussian Filter $ {w}_{s} \left( i - m, j - n \right) $ and we have the Range Filter $ {w}_{r} \left( i - m, j - n \right) $ .

Assuming we fixed the Spatial Filter with certain Radius and parameter $ {\sigma}_{s} $ , let's analyze the effect of the Range Filter.

If we have $ {\sigma}_{r} \to \infty $ then the Range Filter has same value for any pixel and we basically have Spatially Gaussian Filter which is LPF. For $ {\sigma}_{r} \to 0 $ we'll have zero weight for any pixel which is not $ \left( i, j \right) $ , which means Delta Filter (Identity Filter). Namely no effect at all.

So the Bilateral Filter is behaving, per patch, as something between Identity Filter to LPF Filter.

Empirical Analysis of the Bilateral Filter on Patches

Let's take the Lenna Image and analyze, empirically, the Bilateral Filter over few patches.

The Lenna and selected patches for analysis Image is given by:

Let's see how the weights and the Frequency Domain looks:

As can be seen in the results above, the Bilateral Filter is indeed data dependent. We chose different patches (2 Steps, Texture and Flat) and can see how it behaves for each.

If we look on the Frequency Domain, unless the rangeStd parameter is very low or the patch have high variance it looks like LPF behavior.

The Bilateral Filter isn't a classic Linear Spatialy Invariant filter. Hence it can not be classified like classic filters. Yet according to the analysis above one could come to this conclusion:

• When the Bilateral Filter indeed smooths (The rangeStd parameter is modes relative to the data variance) it behaves, at the patch level, like LPF filter.
• When the rangeStd is very low compared to the variance of the data in the patch the Bilateral Filter behaves almost as the Delta Filter (Identity).

The main idea here is since this is Spatially Variant filter we have to analyze it on the Patch Level and not the Image Level.

The full code is available on my StackExchange Signal Processing Q60916 GitHub Repository (Look at the SignalProcessing\Q60916 folder).

I’d say it is a variation of lowpass filters. It tries to average some neighbourhood eg in order to reduce variation caused by noise, but it restricts the contribution different from a LTI filter.

Ie having only positive weights makes it a «kind of lowpass» to my mind.

I am aware that this definition would fit with a positive comb filter, but then that depends on what range of frequencies is the main motivation for employing a comb filter.

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• Elementary Electronic Questions

FILTER design---BPF,BRF

• Thread starter electronics_kumar
• Start date Dec 24, 2005
• Dec 24, 2005

electronics_kumar

Advanced member level 2.

ideal filter characteristics, lpf, bpf, hpf I GOT WHILLE REFERRING FILTER DESIGN THAT FILTERS SUCH AS BPF & BRF CAN BE BUILT BY CASCADING LPF & HPF....WITH STRIGENT REQUIREMENTS THAT FOR BRF---LPF FOLLWOED BY HPF WHEREAS BPF----HPF FOLLOWED BY LPF. WHAT WILL HAPPEN IF WE INTERCHANGED LPF,HPF POSITON TO REALIZE THE BPF AND BRF IE is it possible to realize BPF ---->LPF follwed by HPF BRF ----->HPF follwed by LPF  

• Dec 25, 2005

JoseLeonardo

Full member level 1.

cascading lpf and hpf You can read "Design with Operational Amplifiers and Linear Integrated Circuit" by Sergio Franco.  

Full Member level 2

brf filter theortically speaking it will not affect anything on the system that you have there, but the only thing that could affect it is the cut off frequency of the two filters, once its equal  

• Dec 27, 2005

Advanced Member level 4

bpf lp hp electronics_kumar, Consider the case of a BRF consisting of ideal (Brickwall) LPF and HPF. If the HPF came first, all low frequencies below the high pass cutoff frequency would be rejected. There would be nothing for the LPF to pass. A similar argument holds for the BPF. If the LP filter came first, all high frequencies above the low pass cutoff frequency would be rejected. There would be nothing for the HPF to pass. ~ In the real world, where brickwall filters are not attainable, it is possible (but not a good idea) to reverse the order. Consider the case of a BPF with 6 db/octave slopes. If the LPF comes first, the HPF would have to be a 2nd order filter. One order cancels the 6db slope of the the 2nd order provides the additional 6db/octave. ~ This 2nd paragraph of this explanation applies to the case where the BPF, BRF is implemented by cascading LP,. HP filters. Regards, Kral  

10kangstroms

Member level 5.

lfilter design bpf I'm no filter expert, but I don't think the other responders here are either. I can't see how it would be possible to make a band-reject filter by cascading HP and LP sections. They have to be in parallel. The only reason I can see for the LP-HP order in a BPF is in the case of an active filter, where fast risetimes would be more likely to overload a HPF if it were first in line, while placing the LPF first would eliminate this possibility. It really depends on the content of the signal to be filtered. If the signal has large low frequency content and small high frequency content, perhaps the HPF-LPF order would be preferable.  

• Jan 2, 2006

Newbie level 4

The answer is in this book: L.P. Huelsman "Active and Passive Analog Filter Design". In this book you will find many examples.  

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Home > Books > Diseases of Pleura

Bronchopleural Fistula: Causes, Diagnoses and Management

Submitted: 19 February 2019 Reviewed: 18 June 2019 Published: 06 August 2019

DOI: 10.5772/intechopen.88127

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Diseases of Pleura

Edited by Jelena Stojšić

To purchase hard copies of this book, please contact the representative in India: CBS Publishers & Distributors Pvt. Ltd. www.cbspd.com | [email protected]

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Bronchopleural fistula (BPF) is a pathological communication between the bronchial tree and pleural space. This clinical condition, which has high mortality and morbidity, is one of the major therapeutic challenges for clinicians even today. BPF may result from a lung neoplasm, necrotizing pneumonia, empyema, blunt and penetrating lung injuries, and a complication of surgical procedures. Lung resection is the most common cause of BPF, and this chapter will focus more on this topic. Frequency ranges from 4.5 to 20% after pneumonectomy and from 0.5 to 1% after lobectomy. Several risk factors have been defined in the development of postoperative BPF; preoperative radiotherapy, pulmonary infection, diabetes, right pneumonectomy, a long bronchial stump, residual cancer at the stump (R1 and R2 resection), and the need for postoperative ventilation (especially with high PEEP). BPFs are divided, based on the time elapsed since surgery, into early or late fistula. This grouping is important in management of patient treatment. In early BPF, surgical treatment is generally the preferred treatment modality, whereas in late BPF, conservative approach is preferred. The management of BPF is still one of the most complex challenges encountered by the thoracic surgeons; so prevention is the best way to manage postoperative BPF.

• bronchopleural fistula
• complication
• lung resection

Author Information

Güntuğ batıhan *.

• Department of Thoracic Surgery, Dr Suat Seren Chest Diseases and Surgery Medical Practice and Research Center, University of Health Sciences, Izmir, Turkey

Kenan Can Ceylan

*Address all correspondence to: [email protected]

1. Introduction

Bronchopleural fistula (BPF) has been defined as a direct communication between the bronchus and pleural cavity. Some authors have grouped BPFs as central and peripheral according to their locations [ 1 ]. While a central BPF defines connection between pleura and tracheobronchial three, a peripheral BPF defines connection between the pleura and airway distal to segmental bronchi or lung parenchyma. In literature, the term of “alveolopleural fistula” is also used to describe peripheral BPFs.

Nonsurgical conditions like trauma, chronic necrotizing pneumonia, empyema, radiotherapy, bulla, or cyst rupture can cause BPF, but the most common cause is lung resection. Frequency ranges from 4.5 to 20% after pneumonectomy and from 0.5 to 1% after lobectomy. BPF-related mortality ranges from 18 to 71% in the literature [ 2 , 3 , 4 ]. Because of high morbidity and mortality rates, it is important to define risk factors and apply preventative methods especially in groups of risky patients.

Many authors have divided postoperative BPFs into two groups according to time of onset. There is no consensus about these definitions in the literature, but generally, early BPF was defined as fistula occurring within 30 days after the initial operation. Late BPF was defined as fistulas occurring after more than 30 days. It is established that early BPFs are most commonly associated with a failure in surgical technique and mostly, it can be repaired with reoperation [ 1 , 3 , 5 ].

Late BPFs are typically secondary to patient-related factors and almost always coexist with empyema, and it usually required complex, long-term, and exhausting treatment process for both the patient and the surgeon.

2. Risk factors

BPF is most commonly encountered after lung resections; therefore, establishing risk factors is important to prevent patients from this highly mortal complication.

Numerous risk factors have been associated with BPF development in the literature [ 3 , 4 , 5 , 6 ]. We divided these risk factors into three groups: patient-related factors, surgeon-related factors, and anatomic factors.

Age (>60), gender (male), neoadjuvant radiation therapy, diabetes mellitus, malnutrition, smoking, chronic steroid/immunosuppressive usage, and need for postoperative mechanic ventilation can be classified as a patient-related risk factor. Induction chemotherapy has been cited as a risk factor for postpneumonectomy BPF but there is not any increased risk for bronchoplastic procedures.

A large number of studies have reported an increased risk for BPF due to postoperative mechanical ventilation usage after pneumonectomy. Therefore, to prevent bronchial stump from barotrauma extubation must be achieved at the earliest time after surgery.

A low forced expiratory volume in 1 second and low carbon monoxide diffusing capacity were also defined as risk factors for postoperative BPF occurrence.

According to cadaveric studies, presence of two left-sided and one right-sided bronchial artery supply is the most common configuration.

While the left main bronchus is protected under the aortic arch and surrounded by mediastinal tissue, the right bronchial stump has no such coverage.

The right main bronchus is wider, and more vertical than the left main bronchus. This condition facilitates secretion retention on the right main bronchial stump.

Early BPFs are usually related with technical failure during surgery. The most common causes of this condition are poorly secured knots, stapler misfiring, and high anastomotic tension. Other surgeon-related risk factors are extensive mediastinal lymphadenectomy and peribronchial dissection, long bronchial stump and not coverage the bronchial stump with viable tissue.

3. Clinical presentations and diagnosis

The size and the time of occurrence of the BPF are major determinants of the clinical presentation but, patients often have infection-related symptoms like: fever, cough with serosanguinous or purulent sputum, night sweats, and chills.

Expectoration and respiratory symptoms typically worsen with the patient lying on the side opposite to the one involving the fistula. Flooding of the infected contents of the pleural space to the contralateral lung can lead to severe pneumonia or respiratory distress syndrome.

If the patient has a chest tube massive and prolonged air leakage would be an important clinical clue for BPF.

White blood cell count and systemic inflammation markers are often elevated.

Chest radiogram often revealed a decrease in the fluid level and enlargement in the ipsilateral pleural cavity. Due to the contamination of the contralateral lung by the infected content of the pleural cavity, parenchymal infiltration can be seen.

Computed tomography of the chest can depict mediastinal emphysema, parenchymal infiltration, and enlargement of the pleural cavity, but its success at demonstrating the presence of the BPF is controversial. By the imaging of the continuation of a bronchus or the lung parenchyma to the pleural space, definitive diagnosis of the fistula can be made ( Figures 1 and 2 ). Westcott et al. reported sensitivity of the chest CT as 50% at demonstrating the presence of the peripheral BPFs. Seo et al. reported that chest CT succeed to demonstrate direct or indirect signs of BPF 86% of the patients with central, and 100% of the patients with peripheral BPFs [ 7 , 8 ].

Left sided BPF is seen in the Chest CT. BPF may not always be as clear as this CT image.

Another chest CT image shows right sided BPF. Chest CT also allows the examination of the remaining lung for possible pneumonic infiltrations and metastases.

In the presence of clinical or radiological suspicion of BPF, bronchoscopy must be applied to examine the bronchial stump. Presence of pleural fluid leakage or/and air bubbling in the bronchial stump is pathognomonic ( Figures 3 and 4 ).

Bronchoscope view of the left-sided BPF (arrow) (Asterix shows the main carina). In bronchoscopy, the fistula patency may not always be clearly seen. Air bubbles originating from the stump of the bronchus may be the only sign of the BPF.

Bronchoscope view of the right-sided BPF (arrow) (Asterix shows the main carina).

Reconstruction of 2-dimensional, helical CT images provides noninvasive intraluminal evaluation of the bronchus named as “virtual bronchoscopy” [ 9 ]. This technique can provide additional benefits, especially, planning endobronchial instrumentation, but it is not an essential diagnostic method of fistula.

Less frequently 133 xenon or 99 technetium ventilation scintigraphy can be used to identify BPF by visualization of the radioactive isotopes in the empty pleural cavity. Mark et al. used 99 technetium ventilation scintigraphy in 28 postpneumonectomy patients for the detection of BPF and reported sensitivity of 78% and a specificity of 100% [ 10 , 11 ]. Although, this is a noninvasive diagnostic procedure, it is not practical and easy-to-use, and has no additional benefit to the detection of underlying lung disease.

4. Management

The management of the BPF needs prolonged hospitalization, complex surgical procedures, and close follow-up, but first step in the treatment is management of the life-threatening conditions like sepsis, tension pneumothorax, and respiratory failure. Protection of the contralateral lung from aspiration of the pleural fluid is important to reduce the risk of pneumonia and respiratory failure. Therefore, chest tube must be applied to ensure the drainage of the pleural cavity. Broad spectrum antibiotic therapy against Gram-Positive, Gram-Negative, and anaerobic microorganisms must be initiated, and it should be tailored based on the results of culture-antibiograms.

Early BPFs are mostly associated with failure in the surgical technique. Repairment of the bronchial stump with re-operation is the best treatment modality in these patients.

Patients with late BPF mostly have poor medical condition and major surgical approaches cannot be applied. Conservative treatment modalities like drainage and reduction of the pleural space, pleural irrigation, antibiotics, and nutritional supplementation. Boudaya et al. reported their experience with conservative management of postresectional BPF in 17 patients and BPF is successfully closed in 16 patients [ 12 ].

Various endoscopic techniques for the control of small BPFs have been reported, especially in patients with poor condition. Sealants, fibrin glue, coils, and endobronchial silicon or metal stents have been used to treat small BPFs (ranging from 0.8 to 1.0 mm). Dutau et al. used self-expanding metal stents in seven patients with large fistulas (>6 mm) and reported improvement in patients’ respiratory parameters in early postoperative period [ 13 ].

4.1 Surgical interventions for infection control

Besides conservative treatments, several surgical procedures to treat BPFs have been defined in the literature. Main objectives in these surgical interventions are debridement of the pleural space, minimizing the residual pleural cavity, closure of the fistula, and reinforcement of the bronchial stump with autologous tissue.

Medical condition of the patient

Time of onset of the fistula

Size and localization of the fistula

State of the pleural cavity

4.1.1 Video-assisted thoracoscopic surgery (VATS)

In the presence of pleural infection together with the fistula, tube-thoracostomy must be applied in all cases. Pleural irrigation with antibiotic and povidone-iodine solutions is suggested in sterilization of the infected postpneumonectomy pleural cavity but this treatment modality alone cannot provide sufficient debridement, especially in patients with late fistulas and cause prolong hospitalization.

VATS is a useful method to obtain drainage and debridement of the infected pleural cavity. Single port is usually sufficient in most cases; material and debris can be safely removed with surgical instruments and in the presence of small BPFs (<3 mm) fibrine glue can be applied. Hollaus et al. applied videothoracoscopic debridement in nine patients and defined it as an efficient method to treat postpneumonectomy empyema [ 14 ]. Gossot et al. reported series of 11 patients with postpneumonectomy empyema. These 11 patients underwent videothoracoscopic debridement and 8 of 11 patients discharged without need of additional surgical procedures [ 15 ]. These similar studies have shown that VATS is a feasible option for treatment in select patients with PPE and small BPF.

4.1.2 Open window thoracostomy

Segmental resection of 2–3 ribs

Creation of a skin flap (Muscle should be preserved if possible)

Marsupialization of the cavity

With this procedure, epithelialized thoracostomy window is obtained and effective drainage is ensured.

After this operation, the wound is packed at least daily with gauze moistened with normal saline. Granulation tissue in the wound begins to form over time and when the pleural space is clean closure of the window can be considered.

It is very important to have a good cooperation with patient and relatives for this treatment modality and they should be informed that this treatment procedure may require several weeks.

4.1.3 Clagett procedure

Clagett and Geraci described a two-step treatment technique for the management of postpneumonectomy empyema in 1963 [ 18 ]. Step 1 contains the open window thoracostomy to drain the septic cavity. Step 2 contains obliteration of the pleural cavity with antibiotic solution. Pairolero and Arnold has modified this procedure and described transposition of a well-vascularized extrathoracic muscle as an intermediate step [ 19 ]. With this modification, further reinforcement of the bronchial stump was ensured.

Clagett procedure shows a success rate (OWT closed without PPE recurrence) of 61–89% with a mortality rate between 0 and 24% in the literature.

4.2 Surgically closure of a bronchopleural fistula

Large BPF can cause loss in the tidal volume, aspiration of infected pleural fluid, and respiratory distress. Therefore, bronchial defect must be controlled, especially in patients with large fistulas, for this purpose, two major approaches were defined in the literature.

4.2.1 Transpleural approach

Transpleural approach is the most common method to closure of the BPF ( Figure 5 ). First, BPF must be identified. By careful dissection, bronchus must be mobilized as close to the carina as possible to provide adequate length. Aggressive dissection and devascularization of the proximal bronchus should be avoided because of the risk of failure of the repair and recurrence of BPF. Stapler devices can be used if there is a sufficient length in the bronchial stump. Manual suturation also can be applied above the BPF. After repairment, bronchial stump must be buttressed with well-vascularized tissue such as extrathoracic muscle, omentum, or diaphragm flap.

Image of the left thoracic cavity of the patient with BPF and empyema. Pleural debris and plaques covering the chest wall are seen (Asterix). Infected vascular stumps also are seen (arrow).

4.2.2 Transsternal transpericardial approach

In some cases, surgical management of BPF may be challenging through a lateral transpleural approach. Presence of short bronchial stumps, left-sided BPF, necrotic bronchial stumps and/or history of prior BPF closures via thoracotomy are the main reasons that make transpleural approach difficult. In these cases, transsternal transpericardial approach would be a good alternative to transpleural approach [ 20 ,  21 ]. This approach provides work in healthy, inflammation-free planes. Therefore, in this technique, isolation of the airway is easier and safer than others. Biggest benefit of this technique is that it provides the opportunity to work in a healthy plane. Retraction of the superior vena cava and aorta laterally provide sufficient exposure to make a successful repairment. It is also possible to achieve transpericardial approach by anterior thoracic incision with division of multiple costal cartilages which was described by Padhi and Lynn [ 22 ]. This approach was found to be a difficult and complicated compared to transsternal approach. Therefore, transsternal transpericardial approach has become more widely used among surgeons in the repairment of BPF.

4.2.3 Thoracoplasty

One of the major concerns in the treatment of the BPF is obliteration of the persistent space after control of pleural infection. Thoracoplasty is originally considered as a treatment for active tuberculosis but this procedure is also functional for obliterate pleural space with the viable tissue of the chest wall in the cases of BPF. This is achieved by resection of multiple ribs. Traditional thoracoplasty requires removal of the first 11 ribs periosteum, and intercostal muscles with associated neurovascular bundles. After removal of these structures, skin and thoracic muscles fill the pleural cavity. As can be expected, this procedure has high mortality and morbidity rates and is now abandoned. Removing fewer than five ribs named as “tailored” thoracoplasty is still in use especially in the treatment of chronic BPFs [ 23 , 24 ].

It would be rational to use these treatment modalities in combination to deal with space problem. Tailored thoracoplasty, muscle transposition, omentoplasty, and diaphragm flabs can be used and combined with each other. Clinical condition and performance status of the patient are also important for selection of the best method in the treatment of BPF.

5. Bronchoscopic management of BPF

Various endoscopic techniques like bronchoscopic application of sealants, fibrin glue, silver nitrate cautery, coils, and endobronchial stents for the control of small BPFs have been reported [ 25 , 26 , 27 , 28 , 29 ]. There is no consensus on which method is most effective for BPF closure. We use endoscopic techniques only for the patients with poor clinical condition and not for proper major surgical intervention. Proper technique must be selected depending on the length of the bronchial stump, the location, and size of the fistula ( Figures 6 and 7 ).

Image of the customized (closed in one side with a stapler) silicone stent.

Left-sided BPF was closed with customized silicone stent. After this procedure, air drainage from the chest tube was decreased and respiratory condition of the patient was improved.

We often prefer metallic J-stents and silicon Y-stents ( Figure 8 ). The most seen complication of these stents is migration and occlusion with secretion. Migration and occlusion of the stent can cause severe respiratory distress. Retention of the secretion can also cause contamination of the remaining lung and resulted in severe pneumonia.

Bronchoscope image of the right-sided BPF. It was closed with self-expandable metallic stent.

Despite these complications, in selected patients, endobronchial stents can reduce air leakage and prevent remaining lung from contamination with pleural fluid.

6. Prevention of bronchopleural fistula in pulmonary resection-bronchial stump coverage

To prevent postpneumonectomy bronchopleural fistula, coverage of the bronchial stump is recommended, especially for patients with high risk of BPF.

Pedicled intercostal and extrathoracic muscles, diaphragm, pericardium, pericardial fat pad, and pleura can be used to make a flap to coverage the bronchial stump [ 30 , 31 , 32 ]. There is no consensus for best bronchial stump coverage method and related techniques with several complications were defined in the literature. Diaphragm flaps can cause visceral herniation. The pedicled intercostal muscle flap is useful method for coverage of the bronchial stump but developing heterotopic ossification can cause severe problems. Omentum is a great tissue to promote re-vascularization and healing of the bronchial stump but it requires the opening of the abdominal cavity [ 33 ]. Pericardial fat pad coverage appears to be safe and feasible when compared with other coverage techniques ( Figures 9 and 10 ). It can be applied without risk of additional comorbidity and composes a mechanical barrier between bronchial stump and pleural cavity.

Pericardial fat pad (Asterix) is very useful material to coverage of the bronchial stump. It is dissected from surrounding tissues by preserving the vascular pedicle. Once the fat pad has been mobilized, it is then rotated over the hilum to cover the bronchial staple line (arrows).

The view of the thoracic cavity after coverage of the left main bronchial stump.

7. Conclusion

In modern thoracic surgery, bronchopleural fistula is still associated with significant morbidity and mortality. Treatment techniques have evolved and there are many options to use in patients with BPF, therefore surgeon must evaluate clinical status of the patient, the size, and location of the BPF and the status of the pleural cavity to select the treatment method that will show the most benefit.

It is important to remember that the best treatment is to prevent the disease. Therefore, rigorous surgical technique and bronchial stump coverage are the main steps in the treatment.

Conflict of interest

The authors declare no conflict of interest.

Appendices and nomenclature

• 1. Okuda M, Go T, Yokomise H. Risk factor of bronchopleural fistula after general thoracic surgery: Review article. General Thoracic and Cardiovascular Surgery. Dec 2017; 65 (12):679-685. DOI: 10.1007/s11748-017-0846-1. [Epub 2017 Oct 12]
• 2. Deschamps C, Bernard A, Nichols FC 3rd, et al. Empyema and bronchopleural fistula after pneumonectomy: Factors affecting incidence. The Annals of Thoracic Surgery. 2001; 72 :243-247 [discussion: 248]
• 3. Pforr A, Pages PB, Baste JM, et al. A predictive score for bronchopleural fistula established using the French database EPITHOR. The Annals of Thoracic Surgery. 2016; 101 :287-293
• 4. Wright CD, Wain JC, Mathisen DJ, et al. Postpneumonectomy bronchopleural fistula after sutured bronchial closure: Incidence, risk factors, and management. The Journal of Thoracic and Cardiovascular Surgery. 1996; 112 :1367-1371
• 5. Asamura H, Naruke T, Tsuchiya R, et al. Bronchopleural fistulas associated with lung cancer operations. Univariate and multivariate analysis of risk factors, management, and outcome. The Journal of Thoracic and Cardiovascular Surgery. 1992; 104 :1456-1464
• 6. Martin J, Ginsberg RJ, Abolhoda A, et al. Morbidity and mortality after neoadjuvant therapy for lung cancer: The risks of right pneumonectomy. The Annals of Thoracic Surgery. 2001; 72 :1149-1154
• 7. Wescott JL, Volpe JP. Peripheral bronchopleural fistula: CT evaluation in 20 patients with pneumonia, emphyema, or postoperative air leak. Radiology. 1995; 196 :175-181
• 8. Seo H, Kim TJ, Jin KN, Lee KW. Multi-detector row computed tomography evaluation of bronchopleural fistula: Correlation with clinical, bronchoscopic, and surgical findings. Journal of Computer Assisted Tomography. 2010; 34 :13-18
• 9. Gaur P, Dunne R, Colson Y, Gill R. Bronchopleural fistula and the role of contemporary imaging. The Journal of Thoracic and Cardiovascular Surgery. 2013; 148 . DOI: 10.1016/j.jtcvs.2013.11.009
• 10. Nielsen KR, Blake LM, Mark JB, DeCampli W, McDougall IR. Localization of bronchopleural fistula using ventilation scintigraphy. Journal of Nuclear Medicine. 1994; 35 :867-869
• 11. Raja S, Rice TW, Neumann DR, Saha GB, Khandekar S, MacIntyre WJ, et al. Scintigraphic detection of post-pneumonectomy bronchopleural fistulae. European Journal of Nuclear Medicine. 1999; 26 :215-219
• 12. Boudaya MS, Smadhi H, Zribi H, et al. Conservative management of postoperative bronchopleural fistulas. The Journal of Thoracic and Cardiovascular Surgery. 2013; 146 :575-579
• 13. Dutau H, Breen DP, Gomez C, et al. The integrated place of tracheobronchial stents in the multidisciplinary management of large post-pneumonectomy fistulas: Our experience using a novel customised conical self-expandable metallic stent. European Journal of Cardio-Thoracic Surgery. 2011; 39 :185-189. DOI: 10.1016/j.ejcts.2010.05.020
• 14. Hollaus PH, Lax F, Wurnig PN, et al. Videothoracoscopic debridement of the postpneumonectomy space in empyema. The European Journal of Cardio-Thoracic Surgery. 1999; 16 :283-286
• 15. Gossot D, Stern JB, Galetta D, et al. Thoracoscopic management of postpneumonectomy empyema. The Annals of Thoracic Surgery. 2004; 78 :273-276
• 16. Robinson S. The treatment of chronic non-tuberculous empyema. Surgery, Gynecology & Obstetrics. 1916; 64
• 17. Eloesser L. An operation for tuberculous empyema. Surgery, Gynecology & Obstetrics. 1935; 60 :1096-1097
• 18. Clagett OT, Geraci JE. A procedure for the management of postpneumonectomy empyema. The Journal of Thoracic and Cardiovascular Surgery. 1963; 45 :141-145
• 19. Pairolero PC, Arnold PG, Trastek VF, et al. Postpneumonectomy empyema. The role of intrathoracic muscle transposition. The Journal of Thoracic and Cardiovascular Surgery. 1990; 99 :958-966 [discussion: 966-8]
• 20. Deschamps C, Allen MS, Miller DL, et al. Management of postpneumonectomy empyema and bronchopleural fistula. Seminars in Thoracic and Cardiovascular Surgery. 2001; 13 :13-19
• 21. Abruzzini P. Trattamento chirurgico delle fistole del bronco principale consecutive a pneumonectomia per tubercolosi. Chirur Torac. 1961; 14 :165-171
• 22. Padhi RK, Lynn RB. The management of bronchopleural fistulas. The Journal of Thoracic and Cardiovascular Surgery. 1960; 39 :385-393
• 23. Goldstraw P. Treatment of postpneumonectomy empyema: The case for fenestration. Thorax. 1979; 34 :740-745
• 24. Estlander JA. Sur le resection des cotes dans l’empyeme chronique. The Medico-Chirurgical Review. 1891; 8 :885-888
• 25. Lois M, Noppen M. Bronchopleural fistulas: An overview of the problem with special focus on endoscopic management. Chest. 2005; 128 :3955-3965
• 26. Jones NC, Kirk AJ, Edwards RD. Bronchopleural fistula treated with a covered wallstent. The Annals of Thoracic Surgery. 2006; 81 :364. DOI: 10.1016/j.athoracsur.2004.09.054
• 27. Klotz LV, Gesierich W, Schott-Hildebrand S, et al. Endobronchial closure of bronchopleural fistula using Amplatzer device. Journal of Thoracic Disease. 2015; 7 :1478-1482
• 28. Hamid UI, Jones JM. Closure of a bronchopleural fistula using glue. Interactive Cardiovascular and Thoracic Surgery. 2011; 13 :117-118. DOI: 10.1510/icvts.2011.270397
• 29. Amaral B, Feijó S. Fistula of the stump: A novel approach with a “stapled” stent. Journal of Bronchology and Interventional Pulmonology. 2015; 22 :365-366. DOI: 10.1097/LBR.0000000000000172
• 30. Klepetko W, Taghavi S, Pereszlenyi A, et al. Impact of different coverage techniques on incidence of postpneumonectomy stump fistula. European Journal of Cardio-Thoracic Surgery. 1999; 15 :758-763
• 31. Anderson TM, Miller JI Jr. Use of pleura, azygos vein, pericardium, and muscle flaps in tracheobronchial surgery. The Annals of Thoracic Surgery. 1995; 60 :729-733
• 32. Anderson TM, Miller JI Jr. Surgical technique and application of pericardial fat pad and pericardiophrenic grafts. The Annals of Thoracic Surgery. 1995; 59 :1590-1591
• 33. Okumura Y, Takeda S, Asada H, et al. Surgical results for chronic empyema using omental pedicled flap: Long-term follow-up study. The Annals of Thoracic Surgery. 2005; 79 :1857-1861. DOI: 10.1016/j.athoracsur.2005.01.001

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Your Complete Guide To Blood Flow Restriction Training!

There's been a lot of buzz about blood flow restriction training over the last few years, but many people are still in the dark. Get the details in this comprehensive guide from Dr. Jacob Wilson!

Since the first time I wrote about it on this site two years ago, blood flow restriction (BFR) training has become increasingly popular in weight rooms around the world. However, that doesn't mean that it's perfectly understood. In fact, given the many different names (occlusion training, hypoxic training, KAATSU), styles (bands, cuffs, ace bandages), and goals associated with this type of training, the confusion seems to be growing.

After researching BFR for years and studying it firsthand in the lab, I believe it has a lot to offer to a wide range of people who want to gain muscle, increase their training frequency, and try something new in their programming.

Researchers have been digging into the details of BFR for decades, but there's also fascinating new research happening in this area all the time. That's why I'm devoting an entire guide to answering the most common questions I hear about BFR. My goal is for you to have no excuse not to know what's going on in this exciting part of the training world!

I invite you to ask any question you have that didn’t make it into this article, just as I did with my ketogenic dieting article . Just hit me up at @themuscleprof on Instagram, and I’ll respond in a video later this week. Then we’ll post the video here to go along with the article!

What is blood flow restriction and how does it work?

BFR involves wrapping a device such as a pressure cuff, KAATSU device, or even knee wraps around the top portion of a limb to restrict blood flow out of the working muscle. During properly performed BFR, blood is able to enter the muscle via arterial flow; however, the veins are restricted so that blood is partially prevented from leaving the working muscle.

BFR involves wrapping a device such as a pressure cuff, KAATSU device, or even knee wraps around the top portion of a limb to restrict blood flow out of the working muscle.

This arrangement allows for a swelling effect of the muscle, which is the first mechanism of muscle growth I explained in my article, " Mass Class: The Fundamentals of Muscle Growth ".[1] Blood flow restriction also causes a buildup of metabolites, such as lactic acid, that have been shown to directly stimulate muscle growth. And the direct fatigue caused to the muscle forces the nervous system to recruit the largest fast-twitch muscle fibers, which have the greatest capacity to grow.[2]

Is a warm-up or cool-down necessary?

In general, BFR is performed at intensities normally used for a warm-up set, such as 30-50 percent of your one-rep max (1RM). As such, I would recommend a light, general warm-up of around five minutes, such as walking or light cycling, followed by 15 unwrapped repetitions with the weight you will use for your first set of BFR.

What should I use to wrap, and how tightly should I wrap?

Traditionally, BFR involves the use of a specialized inflatable cuff, known as a KAATSU device, to restrict venous blood flow. The advantage to such devices is that you can precisely control the pressure and always replicate it on workouts.

Unfortunately, most individuals do not have access to this sophisticated device, which has led our lab to complete extensive research on what is known as practical BFR (pBFR). Practical BFR involves the use of an elastic wrap to restrict blood flow. In studies, we have used knee and elbow wraps . However, cotton elastic bandages can also be used.

While practical, one concern is that you may restrict both the arteries and veins.[3] Arteries bring blood to the muscle, while veins take blood away. To get the maximal swelling response, you want blood coming to the muscle and staying there. Thus, we want to restrict blood flow to the veins without occluding the arteries. This is important to understand because all of the potential negatives resulting from BFR stem from fully occluding both the veins and arteries. In fact, there is evidence that wrapping tight enough to cause arterial occlusion may actually decrease muscle growth at the site wrapped.[4]

To solve this problem, our lab looked at the effects of perceived pressure on blood flow during pBFR. We used knee wraps on the legs and wrapped subjects at a perceived pressure of 0, 7, and 10 out of 10, with 10 being the tightest you could wrap. We found that for the legs, pBFR at a perceived pressure of 7 out of 10 resulted in venous restriction, but not arterial. We also found that when training under this pressure, the subjects experienced drastically increased cell swelling, recruited more muscle, and had a large amount of metabolic stress.

However, it is important to note that at a perceived pressure of 10 out of 10, both venous and arterial blood flow were totally restricted! For more information on this, please see our Project Mass video on BFR.

Where should I wrap, and how wide should I wrap?

Research has shown that a narrower cuff width (5-9 cm) reduces the risk of occluding the arteries, compared to a wider cuff or wrap (13+ cm).[1] For this reason, I also recommend wrapping at the top of the legs or arms in a layered manner rather than wrapping in a spiral manner all the way down the arm or leg.

The size of your arms or legs will also determine how tightly you should wrap. Research shows that smaller limbs have a greater probability of being arterially occluded. For most people, I recommend wrapping at a 7 out of 10 on the legs and a 6 out of 10 on the arms.

How heavy should I lift with BFR?

The primary advantage to BFR is that you can increase muscle size at very low intensities. In fact, some research found that individuals who walked with BFR at low intensities could actually increase muscle size.[5] However, we have found that resistance training results in greater benefits in muscle and strength than walking.[1]

So how heavy should you lift? Research has shown gains with as little as 20 percent of your 1RM. However, muscle growth in this case is primarily caused in the slow-twitch, not fast-twitch, fibers. One study compared moderate-pressure BFR with 20, 30, and 40 percent of subjects' 1RM. They found that fast-twitch muscle fibers were not maximally recruited until 40 percent. However, other research has shown that lifting at 80 percent 1RM compared to 40 percent does not increase muscle fiber recruitment.[6] In addition, there is less metabolic stress.

Taking all this into account, BFR for maximal muscle growth should likely be performed at approximately 40 and no more than 50 percent of 1RM. However, if you are using BFR as a recovery day, then performing resistance training at 20-30 percent of 1RM will likely still result in benefits in the slow-twitch fibers. This could be important, as these fibers are often difficult to hypertrophy.

Is it better to be "just a little too loose" or "just a little too tight?"

Dr. Carlos Ugrinowitsch and his colleagues did a study that addressed just this topic.[7] Ugrinowitsch was one of the first scientists to study the molecular mechanisms of BFR, and I'm fortunate enough to now have this genius working in my lab.

In the study, the researchers put a cuff on subjects and pumped up the pressure so it was either 40 or 80 percent of the pressure necessary to occlude the arteries. From a practical BFR standpoint, it would be like wrapping at a 4 or 8 out of 10. Then they had the subjects perform with either 20 or 40 percent of their 1RM.

Here is the cool thing: Both the 40 and 80 percent occlusion pressures at 40 percent of 1RM produced the same amount of muscle growth and strength gains. The clear takeaway as I see it is that it's better to be a little loose than too tight.

As long as you wrap at a moderate pressure and utilize intensity approaching 40-50 percent 1RM, you should be fine. However, by wrapping too tight, you run the risk of complete arterial occlusion.[3]

Are there any beneficial effects on nonrestricted limb muscles?

Many people think that BFR training is just for the arms and the legs, but can it be used for the chest, back, and glutes? The short answer is yes, there is an increase in muscle activation in the nonrestricted limb muscle.

How can this be? Simply put, by wrapping the arms or legs, the nervous system senses extreme fatigue in the limbs. As such, your body is going to do whatever it can to maintain force and keep itself from failing. To compensate, your nervous system recruits more muscle from nonrestricted limbs.

For example, research published in Clinical Physiology and Functional Imaging found that restricting blood flow to the arms and performing the bench press actually resulted in a 16 percent increase in muscle activation of the pecs.[8] Research has also found that individuals who train their legs with BFR and follow it with an arm workout actually get more growth in the arms than when training them separately.[9]

While the reason for this is unclear, it is possible that growth factors released from BFR and/or circulating metabolites are able to enhance the metabolic effects in the non-BFR arms. Thus, training chest, back, or glutes with the arms or legs restricted may be beneficial for inducing growth in those muscles.

What are the recovery demands of BFR versus other isolation training?

Our lab was the first to study the effects of practical BFR on recovery demands compared to non-BFR low-intensity training.[3] We found that, while BFR caused greater fatigue immediately after the exercise bout, there were no increases in muscle damage or declines in force or power 24 hours later. Pretty impressive!

BFR training requires individuals to train with very high repetitions (15-30 reps). If you are unaccustomed to such high reps, then that by itself may lead to some muscle damage.

Because this type of training has low recovery demands compared to high-intensity training, it is likely that it can be performed up to every other day, but probably not more than this. In fact, we actually found that 2-3 days of BFR per week was best for gains in strength and muscle.[1]

However, BFR training requires individuals to train with very high repetitions (15-30 reps). If you are unaccustomed to such high reps, then that by itself may lead to some muscle damage.[10] However, it is unlikely that the wraps themselves are increasing recovery demands.

Thus, if you are new to BFR and metabolically demanding training, I would recommend using it once to twice a week. Once adapted, you can use it up to three times a week for a lagging body part.

What's better: doing a BFR-only phase for a muscle group, or alternating strength/hypertrophy/BFR days like you recommend in Project Mass?

My student Ryan Lowery and I actually did a study on this question a few years ago using practical BFR.[11] We found that periodizing with BFR for a few weeks followed by high-intensity exercise resulted in a lot of muscle growth.

However, the rate at which you periodize should be dependent on your training status.[12] Based on past periodization research, I would advise that if you are just starting out, it will likely work just as well to alternate every few weeks as it would alternating every day.[13]

However, as your training experience increases, I'd recommend using the Project Mass plan and switching it up every few workouts instead.

Is it necessary or advisable to go to failure with BFR?

BFR taps into a major growth mechanism by recruiting the larger, fast-twitch muscle fibers. Fast-twitch muscle fibers are activated by either heavy resistance or fatigue. Research shows that the closer you get to nearing failure, the greater fast-twitch muscle-fiber recruitment becomes.[14,15] As such, failure under low-intensity conditions is likely a prerequisite to optimal muscle-fiber recruitment when using BFR.

I recommend saving failure for your final set as opposed to every set of BFR. You might begin with 30 repetitions at 40 percent of your 1-RM, rest 30 seconds, hit 15, repeat, and finally go to failure.

However, as I wrote in " Is Training to Failure Helping or Hurting Me? " failure can be very fatiguing to your central nervous system.[16] Thus, I recommend saving failure for your final set as opposed to every set of BFR. You might begin with 30 repetitions at 40 percent of your 1-RM, rest 30 seconds, hit 15, repeat, and finally go to failure.

I'm no bodybuilder, just someone who wants nice, shapely arms. Are 2-3 BFR sessions a week enough for me to see serious results?

Fortunately, a great deal of research has been done in nonbodybuilders.[1] In these populations, we have found that 2-3 workouts with BFR a week is perfect, so the answer is absolutely!

Should I just do a couple of movements, or a whole BFR workout?

While most studies have looked at BFR on its own, our lab has teamed up with Bill Campbell's lab on two studies to investigate the effects of BFR combined with high-intensity resistance training.[2,17]

In both studies, we found that BFR in combination with high-intensity exercise was an effective method for increasing muscle mass. What's interesting is that in the second study, we replaced 60 percent of the high-intensity training with BFR and found that subjects were still able to increase muscle mass just as effectively as 100-percent high-intensity training.

So what does this mean to you? First, BFR can increase muscle growth, either as a standalone practice or in combination with heavy training. Second, because BFR causes very little muscle damage, it can be used during deloading periods to supplement as much as 60 percent of the high-intensity workload. This will give athletes the ability to progress while allowing their joints and/or injuries to heal.

I normally recommend using BFR as either a light recovery day on its own, as a method to deload and heal, or as a method to finish the muscle at the end of a workout. The finisher method is supported by studies showing that a heavy workout that incorporates a very high repetition set at the end performed at 50 percent of your 1RM can increase hypertrophy and strength compared to high-intensity exercise alone.[18]

To use BFR as a finisher, do an isolation movement such as curls or leg extensions for 4 sets of 30, 15, 15, 15 reps, with 30 seconds of rest between sets, using 20-40 percent of your one-rep max. Perform this 1-3 times per week.

Is BFR safe for my cardiovascular system?

Prior to beginning any exercise program, it's important to have clearance from your physician. As such, all of the recommendations I discuss in this paper are for healthy individuals, free of disease, who already safely incorporate high-intensity resistance exercise into their weekly routine. While the safety and potential benefits of BFR in clinical populations are actively being studied, that discussion is beyond the scope of this article. However, I can address how BFR compares to traditional resistance training for the cardiovascular and nervous systems.

It has been proposed that restricting blood flow causes damage to veins and ultimately impairs long-term blood flow. However, research shows that, while blood flow is restricted during exercise, over time (four weeks) there is an actual increase in the ability to vasodilate and increase blood flow, compared to traditional resistance training alone.[19]

Moreover, with heavy resistance training (80-100 percent 1RM), mean arterial blood pressure has been shown to more than double, with heart rates reaching maximal levels.[20-21] However, research on low-intensity BFR shows an increase in blood pressure and heart rate by only 11-13 percent.[22] As such, traditional resistance exercise results in much greater blood pressure, heart rate, and even cardiac-output changes than low-intensity BFR.

Why the drastic differences? You should understand that, when doing BFR with low-intensity exercise, studies have applied pressures around the limb ranging from 50-230 mmHg.[23] However, during maximal high-intensity exercise, muscles contract so hard that intramuscular pressures average around 500 mmHg, and have been recorded as high as over 1000 mmHg![24,25]

By comparison, general complete arterial restriction occurs at a range of 140-235 mmHg of an externally applied pressure.[23] Moreover, complete blockage of blood flow has been shown to occur with traditional resistance exercise with as low as 50 and 64 percent of an individual's 1RM.

It's important to realize that traditional resistance exercise already results in occlusion of blood vessels during even moderate-force contractions. Therefore, BFR is only mimicking this response at lower intensity levels.

What about blood clots?

Another concern with BFR is that it may cause thrombosis. Thrombosis is the formation of a blood clot inside a blood vessel, which obstructs blood flow. The three major factors thought to cause this are a hyperability to form a blood clot (hypercoagulability), vascular damage, and vascular occlusion of blood flow.

It's important to know that the formation of a clot is caused by the imbalance between coagulation and fibrinolytic (the breakdown of coagulation products) processes. Research with low-intensity BFR has shown that this type of activity does not increase coagulation. In fact, it may actually increase the breakdown of clots (e.g., increase fibrinolytic activity).[22,26,27] So based on what we know now, it appears to be perfectly safe.

Nevertheless, it is definitely important when using BFR that you restrict but do not completely occlude arterial flow. Remember what I said earlier: 40 percent occlusion has been shown to have the same level of benefit as 80 percent, so there's no downside to erring on the side of caution.

Is BFR safe for my nervous system?

This is a common question. In a survey published in Metabolism, a small percentage of BFR training sessions led to numbness in the wrapped limb.[28] This leads to the implication that BFR could be too taxing on the nervous system; however, further studies looking at nerve conduction velocity (speed at which a nerve impulse is transmitted) saw no change following four weeks of BFR at 30 percent of 1RM.[26]

To me, this indicates that several of the BFR training sessions that led to numbness could have been a result of improper wrapping techniques. Learn to do it right, and you should have nothing to fear.

Want to give BFR a go in your workouts, AND have a full plan to follow for muscle and strength gains? Swole and Strong by Mike Hildebrandt incorporates this method of training on top of your classic push, pull, and lower body split for getting all the results you want from consistent training. Follow now on BodyFit now!

• Loenneke JP, Abe T, Wilson JM, Ugrinowitsch C, & Bemben MG (2012) Blood flow restriction: how does it work? Frontiers in Physiology, 3 , 392.
• Loenneke JP, Wilson GJ, & Wilson JM (2010) A mechanistic approach to blood flow occlusion. International Journal of Sports Medicine, 31 (1), 1-4.
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About the Author

Jacob wilson, ph.d., cscs.

Dr. Jacob Wilson, Ph.D., CSCS*D, is a professor and director of the skeletal muscle and sports nutrition laboratory at the Applied Science and Performance Institute in Tampa, Florida...

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