A new device for measurement of pulmonary pressure-volume curves in patients on mechanical ventilation.

Measurement of total (lung plus chest wall) pulmonary compliance is routinely obtained in mechanically ventilated patients by dividing the tidal volume (VT) by the airway pressure (Paw) gradient from end-inspiration to end-expiration. In order to obtain the pressure-volume (P-V) tracing during inspiration, we developed a method using a continuous and slow (1.7 L/min) oxygen inflow. When gas flow is kept constant, changes in lung volume are proportional to time and do not require direct measurement. In 22 patients, P-V curves traced using the continuous-flow method were identical to those obtained from the syringe method. The advantages of the inflow method are simplicity, reproducibility, and better visualization of the initial part of P-V curve.