Alterations of pulmonary vascular resistance were studied using four different methods of mechanical ventilation. A Servo Ventilator 900 C respirator was used for three of these techniques (IPPV, CPPV and PSV); CPAP was performed using a continuous-flow system because of the latter's advantages compared to demand-flow systems. Five patients (aged 64-75) affected by BPCO uncompensation and pulmonary hypertension (PAP 40 +/- 8 mmHg) were included in the study. A complete hemodynamic test was performed in each patient for each of the methods used by inserting a Swan-Ganz catheter through the right-hand internal jugular vein; intrapleural pressure were also measured using an esophageal balloon. The results of the study revealed a low level of tolerance to CPAP. Of the other methods, PSV was found to be particularly useful since it produced significant constant reductions of PVR and increased levels of CO compared to other techniques. These positive hemodynamic effects may be explained by the pattern of intrapleural pressures and the possibility of "self-adjustment" which this method allows.