Resp Care
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High-frequency airway clearance assist devices generate either positive or negative transrespiratory pressure excursions to produce high-frequency, small-volume oscillations in the airways. Intrapulmonary percussive ventilation creates a positive transrespiratory pressure by injecting short, rapid inspiratory flow pulses into the airway opening and relies on chest wall elastic recoil for passive exhalation. High-frequency chest wall compression generates a negative transrespiratory pressure by compressing the chest externally to cause short, rapid expiratory flow pulses, and relies on chest wall elastic recoil to return the lungs to functional residual capacity. ⋯ Yet, despite over 20 years of research, clinical evidence of efficacy for them is still lacking. Indeed, there is insufficient evidence to support the use of any single airway clearance technique, let alone judge any one of them superior. Aside from patient preference and capability, cost-effectiveness studies based on existing clinical data are necessary to determine when a given technique is most practical.
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Effective clearance of inhaled particles requires mucus production and continuous mucus transport from the lower airways to the oropharynx. Mucus production takes place mainly in the peripheral airways. ⋯ The capacity for mucociliary transport is highest in the peripheral airways, whereas the capacity for airflow transport is highest in the central airways. In patients with airways disease, mucociliary transport may be impaired and airflow transport may become the most important mucus transport mechanism.