Hemodynamic effects of extreme positive pressure breathing using a two-pressure flying suit

The central hemodynamics during extreme positve pressure breathing (PPB) with 4.0-9.3 kPa breathing pressures using a two-pressure flying suit was studied with the thermodilution technique. Pressures measured simultaneously in right atrium, pulmonary artery, and systemic circulation increased in proportion to, but somewhat less than, the breathing pressures. A decreased transmural right atrial and pulmonary arterial pressure was found during PPB to be most pronounced during simultaneous counterpressure to the thorax. Stroke volume (SV) as well as cardiac output (CO) decreased successively during PPB, mostly during PPB with more than 4 kPa. Simultaneous counterpressure to the thorax added further hemodynamic effects. During recovery after PPB, a marked compensatory increase in SV and CO was registered. An increased systemic blood pressure and heart frequency was found at all levels of PPB, suggesting that PPB may be of value to increase G tolerance.