The AirPhysio device is a new OPEP device designed and manufactured in Australia (Figure 1). 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 to be fitted. The device is made from a robust polycarbonate plastic, which the manufacturer suggests makes it more durable. It has been designed to sit flat on the benchtop with the mouthpiece elevated for improved hygiene. In a further attempt to improve hygiene the device includes a cap to go over the mouthpiece.
Being new on the market, the performance of the AirPhysio device has not been compared with other PEP devices such as the Flutter.
The aim of this report was to:
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 . In the conducting airways lined by ciliated epithelial cells (hair coated tissue cells in the respiratory track, which move back and forth to help move particles out of the body), secretions are cleared by the mucocillary escalator (a major barrier against infection. Microorganisms hoping to infect the respiratory tract are caught in the sticky mucus and moved up the mucocillary escalator in the respiratory tract up to the pharynx or the part of the throat behind the mouth and nasal cavity and above the esophagus); an essential component of the lung defence protecting the lung and gas exchange regions from inhaled particles and bacteria which may lead to infection. Mucus generating goblet cells produce a mucus film that sits on top of the cilia (hairs in the respiratory tract). 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 or bacteria can be cleared, typically using a forced expiratory technique such as a cough or a huff.
There are a number of airway clearance techniques. The primary aim of these techniques is to shear mucus and excess sputum 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 . Originating in Denmark and defined as 'the PEP technique', Falk et al  described an airway clearance method which required the subject to breathe through a flow dependent PEP device attached to a face mask that created a PEP of between 10 and 20 cmH20 for 12 to 15 breaths.
Theoretically, PEP assists airway clearance several ways:
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 when compared to airway clearance technique of postural drainage and voluntary cough.
The Flutter device is a handheld pipe like device with a stainless steel ball seated in a conical cone inside the bowl of the pipe (Figure 1). A screw top lid with perforations to allow airflow through the device sits on top of the pipe. As the subject breaths 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 and expiratory airflow which coincide with the opening and closing cycle of the ball being seated and lifted from the cone  (Figure 1). It is hypothesised that these additional oscillations may enhance sputum clearance by decreasing the viscoelastic properties of sputum and improved 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. However these authors found no difference in patient reported symptoms, quality of life or exacerbations at 6 months . 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. However it is worth noting that one long-term randomised controlled trial of children with cystic fibrosis that compared PEP and OPEP reported greater declines in lung function (forced vital capacity) and greater rates of hospitalisations in individuals that used flutter (ie OPEP) when compared to PEP .
Increasing the ball size on the AirPhysio device from 19-22 mm resulted in an increase in the mean and peak PEP across flow rates and tilt angles (Figure 2). These figures show a similar response for the mean and peak PEP generated by the Flutter device. For the mean PEP the Flutter behaved similarly as AirPhysio 19 and 20 mm balls but was significantly lower than the AirPhysio 22 mm. The heavier ball and the greater flow rate required to lift the ball from cone would have accounted for the higher mean PEP generated by the AirPhysio22 when compared to the Flutter and the smaller AirPhysio ball bearing sizes.
Increasing the flow rate resulted in an increase in the amplitude of PEP for both the AirPhysio and Flutter devices (Figure 2). An increase in the amplitude of PEP reflects a widening of the difference between peak and minimal PEP generated by the device. For the current study we found an increase in the maximal PEP across flow rates for both the AirPhysio and Flutter devices (Figure 2). An increase in the amplitude PEP across flow rates suggests that the rate of increase in the minimal PEP was less than that of the maximal PEP. Indeed whilst not reported in results section, the rate of increase in peak PEP for the Flutter and AirPhysio devices was far greater than the increase in minimal PEP. The rate of increase in peak PEP for the Flutter and AirPhysio 19, 20 and 22 were 0.76, 0.95, 0.98 and 0.92 cmH20/L.min-1 respectively. By comparison the rate of increase in the minimal PEP for the Flutter and AirPhysio 19, 20 and 22 were 0.10, -0.03, -0.08 and -0.10 cmH20/L.min-1 respectively. Simply put, as flow rate increased, peak PEP increased to a greater extent than the minimal PEP generated by each device. For the AirPhysio the ball size did not appear to affect the amplitude. Once again, there were no significant differences in the performance of these devices across a range of tilt angles.Griffith University AirPhysio vs Flutter OPEP Device Report
Figure 2: AirPhysio vs Flutter across different flow rates: Data represents the average of each of five trials across each of the inclination angles. PEP: Positive Expiratory Pressure; Amplitude: Difference between peak and minimum values
Increasing the flow rate from 5 to 10 L.min-1 tended to increase the oscillation frequency whereupon there was a general decline in oscillation frequency for increased flow (Figure 2). Once again, the performance of the AirPhysio and Flutter devices did not appear significantly different across a range of flow and tilt angles. The increase in oscillation frequency from 5 to 10 L.min-1 may be due to this flow rate being near that required to lift the ball from the cone for each of the devices. For the larger AirPhysio ball (22 mm) the flow rate required to lift the ball from the cone at higher tilt angles was nearly 5 L.min-1 and as such this may have impacted on the generated oscillation frequency at this low flow rate.
The flow rates chosen for this particular study were similar to those described in the study by Volsko et al  who compared the Flutter and Acapella OPEP devices across flow rates of 5- 30 Lmin-1. We chose this range of airflows as severe lung disease results in a loss of elastic recoil of the lung and a marked reduction in peak airflow generation. At these low flow rates and tilt angles there is a graded mean PEP response produced by the AirPhysio device with the lowest mean PEP generated by 19 mm ball and the highest mean PEP generated by the AirPhysio22. Across these same tilt angles (0-300), the Flutter device tended to perform between that of the AirPhysio 19 and 20 mm device.
In summary, using mean PEP, peak PEP, amplitude PEP and oscillation frequency as indices of performance, we found that the AirPhysio and Flutter devices behaved similarly across a range of flow rates and tilt angles. Similar to our results, Volsko et al  found that the Flutter and Acapella devices performed similarly across a range of airflows.
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