S A N T È • LÖW E N S T E I N S L E E P T H E R A PY D E V I C E S
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SLEEP MEDICINE | V. ISETTA ET AL.
• The algorithm must also distinguish breathing events from artefacts ( e.g. swallowing, coughing and speaking). Indeed, variation among devices response will depend significantly on the detection of events with no well-established definition, such as flow limitation, the detection of which remains open to interpretation. Therefore, the ability of a device to recognise and classify this event depends on the potential agreement between the specific flow limitation pattern simulated in the bench study and the event definition implemented in the APAP device algorithm. • Once breathing events have been detected, the algorithm should decide when and for how long to modify the applied nasal pressure. The differences observed in this study were, therefore, not unexpected and do not necessarily imply incorrect device performance. For instance, the optimal rate of pressure increase after detection of obstructive events, which varied considerably between the devices tested (figure 3), is not clear. Specifically, a difficult balance needs to be found between a response that is fast enough to ensure avoidance of disturbed breathing and soft enough to avoid patient awakening in response to a sudden nasal pressure increase. In addition, it should be noted that default settings were used during testing of most of the devices in this study and that it is possible that selecting other response thresholds could have an impact on their performance. Whether or not such modifications would increase the number of devices able to normalise breathing under the test conditions used in this study or the values of nasal pressure applied to normalise breathing is unknown. Although bench testing is useful to understand and characterise the response of APAP devices under well-controlled conditions, this evaluation method has some limitations. Defining a model of OSA patient does not allow reproduction of the almost infinite variation in breathing events observed in clinical practice, or uncontrolled mask leaks, snoring or mouth expiration. Accordingly, it is possible that the responses of the tested devices would have been different from those reported if OSA was simulated by another model. In fact, bench testing should be considered a preliminary evaluation before the device is fully assessed in the clinical setting. However, this testing has shown that the high residual AHI seen in some devices should be further investigated in clinical practice to ensure that patients using these devices do have their sleep apnoea effectively treated. Bench test results can thus be useful when selecting the most suitable device for each patient to improve comfort and treatment compliance, and when interpreting the results of clinical studies if different devices are involved. In conclusion, this bench study showed considerable response differences between several currently used APAP devices when subjected to a specific simulated OSA breathing pattern. Although APAP is a useful therapy, these results underline the concept that the actual implementation of APAP depends on the product-specific engineering solutions and algorithms adopted by each manufacturing company, which has implications for clinical application.
Lessons for clinicians
• This bench test study assessed how currently available APAP devices respond to a simulated OSA patient. Regardless of the simplified experimental setting employed in this work, as compared with the complexity of events found in the clinical arena when treating OSA patients, the following practical lessons can be derived. • The way that each commercial APAP device modifies nasal pressure when subjected to disturbed breathing patterns is different. • These differences in response among APAP devices are not necessarily caused by incorrect performances. Instead, they are the result of the particular engineering solutions implemented in each device. • Knowing the specific functioning features of each APAP device ( e.g. sensitivity in detecting the different obstructive events, tolerance to events before increasing pressure and speed of pressure changes) may help to understand treatment compliance in specific patient phenotypes. • Choosing the optimal APAP device for the needs/preferences of each individual patient may improve therapy compliance. Acknowledgements The authors wish to thank Miguel Angel Rodriguez (University of Barcelona, Barcelona, Spain) for his technical support in execution of the tests and Nicola Ryan, an independent medical writer funded by ResMed, for her assistance in preparing the manuscript. References 1 Epstein LJ, Kristo D, Strollo PJ Jr, et al. Clinical guideline for the evaluation, management and long-term care of obstructive sleep apnea in adults. J Clin Sleep Med 2009; 5: 263 – 276. 2 Qaseem A, Holty JE, Owens DK, et al. Management of obstructive sleep apnea in adults: a clinical practice guideline from the American College of Physicians. Ann Intern Med 2013; 159: 471 – 483.
ERJ Open Res 2015; 1: 00031 ‐ 2015 | DOI: 10.1183/23120541.00031-2015
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