Acoustic airway clearance devices: A systematic review of experimental and numerical studies

The global respiratory care devices market, including acoustic airway clearance devices (ACDs), is expected to experience a compound annual growth rate of 6.10 % from 2023 to 2030. However, there are a number of inconsistencies in the categorization and working frequency range from one discipline to another one. A better understanding of the mechanisms of action of these devices is therefore of prime importance in order for physicians, physiotherapists, scientists, and engineers to remain abreast of up-to-date studies in the field and specifically on the frequency range used. In the present review, we have categorized acoustic ACDs according to their working principles while reviewing their existing shortcomings in both experimental and numerical studies, thereby paving the way for future research directions. A total of 14 different ACDs are discussed, taking into account their working principle and frequency range, and classified as follows: mechano-acoustic devices, high-frequency chest wall compression (HFCWC), and high-frequency chest wall oscillation (HFCWO) for high-frequency chest compression (HFCC) and oral high-frequency oscillation (OHFO). Existing studies highlight that ACDs with HFCWC distinguish themselves from other devices by supplying compression in a homogeneous manner, allowing the delivery of both efficient and gentle therapy up to approximately 40 Hz. Notwithstanding, a stark difference in the working frequency range across the various devices was found and identified as a literature gap. Given that this difference arises from both experimental and numerical studies between the various disciplines, the studies are further classified according to their respective objectives, methodology and outputs to help readers quickly and straightforwardly locate the articles of interest for potential future investigations. The review also brings to light the interdisciplinary nature of ACDs, whereby numerical biomedical studies can actively assist experimental studies in terms of reproducibility and reliability, creating a digital twin of the human chest and its respective components.