Cardiopulmonary Responses to Pressure Breathing.

Abstract

Investigators at the F. G. Hall Environmental Laboratory of the Duke University Medical Center studied the effects of positive pressure breathing (PPB) on pulmonary gas exchange. Multiple inert gas elimination techniques was used with 10 human subjects to quantify changes in ventilation/ perfusion (Va/Q) relationships during PPB. Subjects wore the Combined Advanced Technology Enhanced Design G Ensemble (COMBAT EDGE) with a 1:1 G-suit to mask pressure ratio. Experimental conditions included breathing air and 100% oxygen at 0, 30, and 60 mmHg of PPB at ground level and breathing 100% oxygen at 0 and 60 mmHg of PPB at 24,900 feet in an altitude chamber. Results showed the following: 1) an almost 5-fold increase in minute ventilation at 60 mmHg mask pressure; 2) PPB caused a shift of ventilation and perfusion to lung units at higher Va/Q's; 3) the data supported the notion that PPB reduces shunt and perfusion to low Va/Q lung units; 4) while oxygen breathing resulted in minor effects on some variables, there was a statistically significant effect of altitude exposure on heart rate, arterial blood pressure, and respiratory effects on hemodynamics; and 5) phasic swings in mask pressure seemed to augment venous return and sustain mean arterial pressures in some subjects during PPB.