EFFECTS OF CONTINUOUS POSITIVE AIRWAY PRESSURE BREATHING ON LUNG-VOLUME AND DISTENSIBILITY

In this study the effect on lung elastic behavior of 10 min of breathing at a continuous positive airway pressure (CPAP) of 10 cmH2O were examined in 10 normal subjects. To investigate whether any changes were induced by release of prostaglandins, the subjects were also pretreated with the cyclooxygenase inhibitor indomethacin. CPAP produced a significant (P < 0.001) upward shift of the pressure-volume (PV) curve [change in total lung capacity (ΔTLC) 374 ± 67 (SE) ml, mean Δvolume at a transpulmonary pressure of 15 cmH2O (ΔVL15) 279 ± 31 ml] with no change in K, an index of lung distensibility. After CPAP the PV curves returned to normal base line within 20 min. The same pattern was observed after indomethacin, but the increase in TLC was significantly less (P < 0.01) (mean ΔTLC 206 ± 42 ml) mainly because of a slight and not statistically significant increase in base-line TLC. In five subjects further PV curves with and without CPAP were obtained ≥7 days after indomethacin. The responses were not significantly different from those obtained before indomethacin (mean ΔTLC 366 ± 89, mean ΔVL15 296 ± 42 ml). We conclude that CPAP produces an upward shift of the PV curve without a change in lung distensibility. In addition, there may be a small degree of resting alveolar duct tone that is influenced by indomethacin.