Positive Expiratory Pressure (PEP) Devices

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Introduction

Positive Expiratory Pressure (PEP) is breathing against resistance, which can be performed either through a device or against pursed lips .

Mechanism of PEP

The increase in pressure is transmitted to airways creating back pressure stenting them during exhalation , therefore preventing premature airway closure thus reducing gas trapping . It promotes collateral ventilation, allowing pressure to build up distal to the obstruction . Not only does PEP retains airways from collapsing and prolongs expiratory flow, it is effective airway clearance promoting movement of mucus proximally .

• _{Collateral Ventilation:Is a phenomenon found in the human lungs where alveolar structures are ventilated through passages or channels that bypass normal airways.}

Types of PEP

Some literature has described PEP as two types varying in pressure range low and high pressure PEP. Low pressure PEP ranges from 5-20cm H2O at mid-expiration, whereas high-pressure PEP ranges from 26-102cm H2O which is achieved by maximal inspiration followed by performing forced expiratory maneuver into PEP mask. Other sources have described PEP as a three airways techniques that has been developed based on expiratory resistance:- PEP, High Positive Expiratory Pressure (HiPEP), and Oscillatory Positive Expiratory Pressure (OscPEP).

• PEP
  • Involves breathing against expiratory resistance to temporarily increase Functional Residual Capacity (FRC)and Tidal Volume (VT)accompanied by clearance techniques such as Forced Expiratory Technique (FET), huffing, and or coughing.
• HiPEP
  • Involves breathing against resistance by augmenting expiratory flow using FVC.
• OscPEP

• • Is a technique that utilizes both PEP when exhaling against resistance and flow oscillation in exhalation.

Indications for PEP

• Acute and chronic respiratory failure for reasons of surgery 
• Neurological or musculoskeletal dysfunction
• Old age and immobility
• To increase lung volume by increasing FRC and VT
• Reduce hyperinflation
• Improve airway clearance

Physiology of PEP

Literature has stated theoretical explanations that discuss the physiology behind PEP therapy and its effects on cardiopulmonary status. The theories are:-

Increasing lung volume FRC and VT

• • A progressively temporary increase in FRC has been found to be proportionally correlated when increasing PEP
  • An increase in FRC is attained by alteration of breathing pattern that is a product of a decrease in expiratory flow and an increase in expiratory time leading to exhalation of smaller volumes.
  • lung volume increase is achieved by altering breathing pattern, thereby increasing VT and decreasing respiratory frequency, which is due to an increase in muscle activity of inspiratory and expiratory muscles.
  • Improved gas exchange is a result of breathing during a prolonged period with normalized lung volumes.

Reduction of hyperinflation

• • Hyperinflation is a result of air entrapment causing the lungs to over inflate. It is caused by muscle spasm, mucosal inflammation, hyper-secretions, reduced lung elasticity due to destruction of lung parenchyma. If Untreated may lead to inspiratory muscle exhaustion, decreased ventilation, and deficient gas exchange.
  • PEP reduces expiratory flow, which in return decreases the declining pressure across the airway wall thereby reducing collapse.
  • Increasing pressure within airways transports EPP centrally and in stable airways therefore stenting them. Reduction of airway collapse increases expired volume leading to additional emptying of lung volume thus lowering FRC and improving ventilation distribution and gas exchange.

Airway Clearance

When using HiPEP

• • It homogenously mobilize secretions in collapsed airways. It aims towards increasing FRC by recruiting collapsed lung volumes and uses resistance to obtain progressive homogenization emptying of the lungs.
  • Homogenization is achieved by the facilitation of EPP to move peripherally during expiration avoiding collapsed airways, trapped gas, and atelectasis. This results in reduction of respiratory flow and an increase in expiratory flow combined with an increase in FRC. In doing so secretion is mobilized in closed or collapsed and unreachable parts of the lungs. HiPEP is proven to be an airway clearance technique equally or more effective than PEP.

When using OscPEP

• The oscillating property is achieved by bursts and turbulent expiratory airflow due to the opening and closing of the valve. Oscillations during expiration decreases the viscoelasticity properties of mucus, effecting its movement which depends on the oscillating frequency.OscPEP is equally as effective as other Airway Clearance Technique (ACT) as PEP and Active Cycle Breathing Technique (ACBT).

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