Normal Airway Clearance Process
The conducting airways (Figure 1) of the respiratory system are lined with hairs, called cilia (Figure 2). Mucus generating goblet cells (Figure 2) produce a mucus film that sits on top of the cilia. The mucus is cleared by the cilia moving back and forth along the conducting airway [called the mucociliary escalator], this action 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.
What Happens with Respiratory Conditions?
Typically, with many lungs diseases, the body creates an excess of mucus secretions.
Asthma – with Asthma (especially Bronchial Asthma, Figure 3), 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.A basic understand of some lung conditions are as follows:
Cystic Fibrosis – The body creates an over-supply of ‘sticky’ mucus secretions which are difficult for the body to remove from the airways naturally.
Chronic Obstructive Pulmonary Disease (COPD)
Chronic Bronchitis – The airways are continually inflamed and produce mucus, which may lead to the cilia (hairs) becoming damaged from smoke, pollution and irritants, degrading the mucociliary escalator and making it harder to remove mucus secretions.
Emphysema – The smoke and pollution cause the alveoli air sac membranes to break down and be coated with carbon deposits. This causes inflammation and mucus secretions in the air sacs, reducing gas transfer. This makes it harder for the lungs to expel due to the absence of the mucociliary escalator in this section of the lungs.
Figure 5 – COPD (Chronic Bronchitis and Emphysema)
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 6)
Figure 6 – Bronchiectasis
How does Airway Clearance Help Lung Disease?
For lung diseases that result in excess secretions, airway clearance techniques and devices are considered to be essential for optimising respiratory status and reducing disease progression .
There are a number of airway clearance techniques and devices including postural drainage, percussion, breathing exercises and positive expiratory pressure (PEP).
How Do Airway Clearance Techniques and Devices Work?
Airway clearance techniques and devices apply external forces to the lungs and airways that manipulate lung volumes, pulmonary pressures and gas flow [2, 3], pushing excess mucus up and out of the smaller airways and into the larger airways, then into the throat to be cleared out of the body .
Positive expiratory pressure (PEP) devices can assist airway clearance in several ways.
- The addition of positive resistive pressure as the participant breathes out results in a longer expiration time, 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 7) resulting in a temporary increase in functional residual capacity (FRC) .
Figure 7 – Collateral Ventilation
- As the individual breathes through the PEP device, FRC (Functional Residual Capacity or the air present in the lungs at the end of passive expiration), 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 combines both PEP and airway oscillation techniques.
AirPhysio OPEP Device
The AirPhysio device is a handheld pipe-like OPEP device which includes several original design features in the device including 3 different versions to allow for differing lung capacities and function.
Figure 8 – Oscillating air of AirPhysio
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 8) It is hypothesised that these additional oscillations may enhance sputum clearance by decreasing the viscoelastic properties of sputum and improve clearance through the airways.
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.
An early study by Konstan and colleagues  described the efficacy of OPEP devices for airway clearance in 18 cystic fibrosis patients. The authors reported there were no adverse events with the device and that patients expelled significantly greater amounts of sputum (mucus) when compared to the airway clearance techniques of postural drainage and voluntary cough.
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 Pt 1): 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.