Effects of continuous negative airway pressure on lung volume and respiratory resistance

Institut National de la Santé et de la Recherche Médicale and Service de Physiologie-Explorations Fonctionnelles, Hôpital Henri Mondor, AP-HP, 94010 Créteil, France This study was designed to determine the responses of lung volume and respiratory resistance (Rrs) to decreasing levels of continuous negative airway pressure (CNAP). Twenty normal subjects were studied in the basal state and under CNAP levels of 5, 10, and 15 hPa. Rrs was measured by the forced oscillation technique (4-32 Hz). End-expiratory lung volume (EELV) and tidal volume (V T ) were measured by whole body plethysmography. Rrs was extrapolated to 0 Hz (R 0 ) and estimated at 16 Hz (R 16 ) by linear regression analysis of Rrs vs. frequency. Specific Rrs, SR 0 and SR 16 , were then calculated as R 0 (EELV + V T /2) and R 16 (EELV + V T /2), respectively. EELV significantly decreased, whereas R 0 , R 16 , SR 0 , and SR 16 significantly increased, as the CNAP level decreased ( P