vPEP Studies
The Importance of Expiratory Flow Bias in Secretion Clearance

Changing the paradigms by which respiratory professionals evaluate OPEP therapy


The Importance of Expiratory Flow Bias in Secretion Clearance

A published study challenges the traditional focus on pressure amplitude as an indicator of the effectiveness of OPEP therapy. Instead of focusing on pressure, the study analyzed maximum expiratory flow during OPEP therapy by comparing flow-volume loops generated by the vPEP against two competitive products during simulated, spontaneous breathing. The study found that, just as in a forced cough, peak expiratory flow is a major factor in improving secretion clearance with OPEP devices.

Expiratory Flow Bias is also important. This is the difference between peak expiratory flow and peak inspiratory flow. Secretion clearance increases when maximum expiratory flow exceeds maximum inspiratory flow during OPEP therapy. The greater the difference, the more effective the secretion clearance, and vice versa. The vPEP provides a superior flow rate difference across five tidal volumes when compared to two competitive products. Charts 1-2 show a bench study using a human lung simulator at various breath sizes with OPEP products at low and high resistance settings.

View video - secretion clearance


Maximizing the Expiratory Flow Bias (VE max - VI max diffference)

Difference at Low Resistance
Difference at High Resistance

Reference: Pursley, D.M., Analysis of Three Oscillating Positive Expiratory Pressure Devices During Simulated Breathing. Respiratory Therapy 2017; Volume 12, No. 1, 52-56.



 

Changing the paradigms by which respiratory professionals evaluate OPEP therapy

A published study1 challenges the traditional focus on pressure amplitude as an indicator of the effectiveness of OPEP therapy. The study utilized a human lung simulator to analyze the vPEP and two competitors against three measures of OPEP effectiveness: flow amplitude, expiratory pressure and the relationship of peak expiratory flow to peak inspiratory flow. The study revealed the superiority of the vPEP against competitors in all measures.

Flow Amplitude
The flow amplitude (along with the frequency) determines the quality of oscillations, which are throught to indicate the degree to which a device reduces mucoviscosity.

In the clinical study, the vPEP showed superior flow amplitudue compared to two competitive device across four inspiratory times.

Difference at Low Resistance

Expiratory Pressure:
The mean expiratory pressure is important in moving air behind obstructions through collateral ventilation channels. In the study, there were significant differences in mean expiratory pressure between the vPEP and two competitive devices across four inspiratory times. Chart 2 summarizes mean expiratory pressure for the three devices and shows the superiority of the vPEP.

PEF/PIF ratio
One of the primary factors for effective secretion clearance is the ratio of peak expiratory flowrate (PEF) to peak inspiratory flow rate (PIF). In order to move mucus cephalad, the PEF must exceed PIF, creating an expiratory flow bias.

In the study, the vPEP produced the highest mean PEF/PIF ratio across all four inspiratory times compared to two competitive products. See chart 3 for a summary of the PEF/PIF ratios for the three devices.

The superior expiratory flow bias of the vPEP was also demonstrated across both high and low resistance in a previously published study2 across five tidal volumes.

Chart 4 shows representative flow-volume loops for the three devices captured at an inspiratory time of 4 seconds, expiratory time of 4 seconds, and a tidal volume of 1200 ml. The red arrow shows the greater flow amplitude for the vPEP. The study suggested that instead of focusing exclusively on the pressure created by an OPEP device, an alternative approach might be to focus on the PEF/PIF ratios and the expiratory flow bias they produce. Keep in mind that just as in a cough, it is actually short bursts of increased expiratory air flow that help move secretions up the airway.3



 

Conclusion: The study found that expiratory flow bias, which occurs when peak expiratory flow exceeds peak inspiratory flow, is a key driver behind moving secretions up the airway, whereas flow amplitude chops secretions up.


Slow Breaths In

In all three devices, as inspiratory time was increased, there was an absolute increase in the PEF/PIF ratio. The greatest mean percent change in PEF/PIF occurred when inspiratory time was increased from 2 seconds to 4 seconds, confirming the clinical recommendations for patients to take slow deep breaths.

The vPEP and all D R Burton OPEP devices feature instructions for use that emphasize the patient to take in very slow deep breaths, deeper than normal.

References:
1. Pursley, D.M. Effect of inspiratory time on PEF/PIF ratio in Three oscillating PEP devices in an adult chronic bronchitis model. Respiratory Therapy 2018; Volume 13, No. 1, 51-54.

2. Pursley, D.M. Analysis of Three Oscillating Positive Expiratory Pressure Devices During Simulated Breathing. Respiratory Therapy 2017; Volume 12, No. 1, 52-56.

3. Hess, Dean. Respiratory Care: Principles and Practice. Sudbury, MA: Jones & Bartlett Learning, 2016. Print.

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