Effect of positive pressure breathing on distribution of pulmonary blood flow and ventilation.

Abstract

The effects of positive pressure breathing on distribution of pulmonary perfusion and ventilation were determined in 6 normal subjects by means of the xenon 133 technique. The subjects were studied under conditions of spontaneous breathing, intermittent positive pressure breathing, and continuous positive pressure breathing. With intermittent positive pressure breathing, a mean inspiratory pressure of 10 mm Hg was achieved with a tidal volume of 1,200 ml. When expiratory resistance was added (continuous positive pressure breathing), functional residual capacity increased by an average of 300 ml; inspiratory pressure was 13 mm Hg, and expiratory pressure was 5 mm Hg. Despite the larger tidal volumes attained with the respirator compared to spontaneous breathing, there were only minimal changes in the normally occurring vertical gradients of perfusion and ventilation/perfusion ratios from apex to base, although there was a slight tendency for ventilation to become more evenly distributed from apex to base w...