(Based on Validation of AirPhysio Oscillating Positive Expiratory Pressure Device Report)
Before we explain how a device works with a process or what can go wrong with this process, we need to explain how the process works.
Normal Airway Clearance Process
The conducting airways (Figure 1) of the respiratory system are lined with hairs, called cilia (Figure 2). The secretions are cleared by the cilia moving back and forth together along the conducting airway, called the mucociliary escalator, an essential component of the lung defence, protecting the lung and gas exchange regions (respiratory zone) from inhaled particles and bacteria which may lead to infection.
Figure 1- Conducting and Respiratory Airways
Mucus generating goblet cells (Figure 2) produce a mucus film that sits on top of the cilia. The rhythmic beating of the cilia acts as an escalator that moves the mucus from the smaller peripheral airways to the larger central airways. From these larger airways, mucus and any trapped inhaled particles (i.e. smoke, pollen, pollution, etc…) or bacteria can be cleared, typically using a forced expiratory technique such as a cough or huff.
Figure 2 – Cilia, Mucus and Goblet Cell
What happens with respiratory conditions?
Typically, with many lungs diseases, the body creates an excess of mucus secretions.
A basic understand of some lung conditions are as follows:
- Asthma – with Asthma (especially Bronchial Asthma), when the airways become hypersensitive from triggers in the air, they can become inflamed and narrow, which also leads to an excess of mucus secretion, which makes it harder for the body to clear naturally.
- Cystic Fibrosis – with Cystic Fibrosis, the body creates an oversupply of sticky mucus secretions which make it hard for the body to clear naturally.
- COPD – with Chronic Bronchitis, the cilia (hairs) can become damaged, degrading the mucociliary escalator and making it harder to remove secretions.
- Bronchiectasis – with Bronchiectasis, the airway walls are damaged, creating pockets for the mucus to be trapped in and thus also degrading the mucociliary escalator and making it harder to remove secretions.
Figure 3 – Normal Airway vs Bronchial Asthma Inflamed Airway
How does airway clearance help lung disease?
For lung diseases that result in excess secretions, airway clearance techniques which improve mucus clearance are considered to be essential for optimising respiratory status and reducing disease progression .
There are a number of airway clearance techniques. The primary aim of these techniques is to shear excess mucus from the inner surface of the airway lumen in the direction of the larger airways . To achieve this, airway clearance techniques apply external forces to the lungs and airways that manipulate lung volumes, pulmonary pressures and gas flow [2, 3]. Examples of airway clearance techniques include postural drainage, percussion, breathing exercises and positive expiratory pressure (PEP).
Positive expiratory pressure devices can be used to assist airway clearance in individuals with excess secretions . Theoretically, PEP assists airway clearance several ways.
- The addition of positive resistive pressure as the participant breathes out results in a prolongation of expiration which in turn may increase expiratory capacity and a reduction in gas trapping .
- Moreover it is proposed that PEP stabilises and splints the airways open  and increases the gas pressure behind excess mucus via collateral ventilation (Figure 4) resulting in a temporary increase in functional residual capacity (FRC) .
Figure 4- Collateral Ventilation
As the individual breathes through the PEP device, FRC is gradually increased . By increasing the gas pressure behind the mucus, forced expiratory techniques may be more effective in moving excess secretions from the peripheral to central airways [1, 7].
Oscillating high frequency PEP (OPEP) devices combine both PEP and airway oscillation techniques. The most well-known OPEP device, the Flutter, originated in Switzerland . An early study by Konstan and colleagues  described the efficacy of the device for airway clearance in 18 cystic fibrosis patients. The authors reported there were no adverse events with the device and that patients expectorated significantly (p<0.001) greater amounts of sputum (mucus) when compared to airway clearance technique of postural drainage and voluntary cough.
Being new on the market, the performance of the AirPhysio device has not been compared with other PEP devices such as the Flutter. The AirPhysio device is a handheld pipe-like device with a stainless-steel ball seated in a conical cone. The manufacturers included several original design features in the device including a dual cone and a modified cap that allows 3 different ball bearings (19, 20 and 22 mm), also to allow for differing lung capacities and function.
As the subject breathes out through the device, the ball moves up and down creating an opening and closing cycle as the stainless-steel ball is lifted off and then reseated on the cone throughout expiration . These opening and closing cycles result in oscillations of endobronchial pressure (pressure in the airways to assist in expanding and opening up the airways) and expiratory airflow (air flowing out of the airways, reducing pressure in the lungs) which coincide with the opening and closing cycle of the ball being seated and lifted from the cone . (Figure 5) It is hypothesised that these additional oscillations may enhance sputum clearance by decreasing the viscoelastic properties of sputum and improve clearance through the airways.
Figure 5 – Oscillating air of AirPhysio
Recent Cochrane reviews in individuals with cystic fibrosis, bronchiectasis and following an acute exacerbation of chronic obstructive pulmonary disease (AECOPD) suggest that airway clearance techniques are safe and may confer some benefit on clinical outcomes [1, 2, 9]. In AECOPD, there was a greater magnitude of the effect for PEP over non- PEP airway clearance techniques on the need for ventilatory assistance and hospital length of stay . In a large randomised controlled trial comparing PEP with no airway clearance during a hospital stay for AECOPD, resting breathlessness improved more rapidly in the group allocated to PEP when compared control in the first 8 weeks following intervention.
The recently published Cochrane review by McIlwaine et al  examined the use of PEP devices in individuals with cystic fibrosis. Using outcomes such as changes in lung function, mucus cleared from the airways and quality of life, the authors reported that efficacy of PEP was similar to other forms of chest physiotherapy. Of note these authors compared the efficacy of PEP and OPEP and found similar results for both techniques.
- Mcllwaine, M. B. Button, and K. Dwan, Positive expiratory pressure physiotherapy for airway clearance in people with cystic fibrosis. Cochrane Database Syst Rev, 2015(6):p.CD003147.
- Osadnik, C.R., C.F. McDonald, A.P. Jones, and A.E. Holland, Airway clearance techniques for chronic obstructive pulmonary disease.Cochrane Database Syst Rev, 2012(3): p. CD008328.
- Pryor, J.A., Physiotherapy for airway clearance in adults. Eur Respir J, 1999. 14(6): p. 141824.
- Falk, M., M. Kelstrup, J.B. Andersen, T. Kinoshita, P. Falk, S. Stovring, and I. Gothgen, Improving the ketchup bottle method with positive expiratory pressure, PEP, in cystic fibrosis. Eur J Respir Dis, 1984. 65(6): p. 423-32.
- Osadnik, C.R., C.F. McDonald, and A.E. Holland, Advances in airway clearance technologies for chronic obstructive pulmonary disease.Expert Rev Respir Med, 2013. 7(6): p. 673-85.
- Oberwaldner, B., J.C. Evans, and M.S. Zach, Forced expirations against a variable resistance: a new chest physiotherapy method in cystic fibrosis. Pediatr Pulmonol, 1986. 2(6):p. 358-67.
- Myers, T.R., Positive expiratory pressure and oscillatory positive expiratory pressure therapies. Respir Care, 2007. 52(10):p. 1308-26;discussion 1327.
- Konstan, M.W., R.C. Stern, and C.F. Doershuk, Efficacy of the Flutter device for airway mucus clearance in patients with cystic fibrosis. J Pediatr, 1994. 124(5 Pt1): p.689-93.
- Lee, A.L., A.T. Burge, and A.E. Holland, Airway clearance techniques for bronchiectasis. Cochrane Database Syst Rev, 2015(11): p. CD008351.