Peak Cough Flow Fails to Detect Upper Airway Collapse During Negative Pressure Titration for Cough-Assist.

Objective: To study the ability of peak cough flow (PCF) and effective cough volume, defined as the volume exsufflated >3 L/s, to detect upper airway collapse during mechanical insufflation-exsufflation (MI-E) titration in neuromuscular patients.

Design: Prospective observational study.

Setting: Rehabilitation hospital.

Participants: Patients (N=27) with neuromuscular disease causing significant impairment of chest wall and/or diaphragmatic movement.

Interventions: The lowest insufflation pressure producing the highest inspiratory capacity was used. Exsufflation pressure was decreased from -20 cm HO to -60/-70 cm HO, in 10-cm HO decrements, until upper airway collapse was detected using the reference standard of flow-volume curve analysis (after PCF, abrupt flattening or flow decrease vs previous less negative exsufflation pressure).

Main Outcome Measures: PCF and effective cough volume profiles during expiration with MI-E.

Results: Upper airway collapse occurred in 10 patients during titration. Effective cough volume increased with decreasing expiratory pressure then decreased upon upper airway collapse occurrence. PCF continued to increase after upper airway collapse occurrence. In 5 other patients, upper airway collapse occurred at the initial -20 cm HO exsufflation pressure, and during titration, PCF increased and effective cough volume remained unchanged at <200 mL. PCF had 0% sensitivity for upper airway collapse, whereas effective cough volume had 100% sensitivity and specificity.

Conclusion: Of 27 patients, 15 experienced upper airway collapse during MI-E titration. Upper airway collapse was associated with an effective cough volume decrease or plateau and with increasing PCF. Accordingly, effective cough volume, but not PCF, can detect upper airway collapse.