Arterial and pulmonary arterial hemodynamics and oxygen delivery/extraction in normal humans exposed to hyperbaric air and oxygen

Abstract

Divers and hyperbaric chamber attendants breathe hyperbaric air routinely. Hyperbaric oxygen (HBO(2)) is used therapeutically frequently. Although much is understood about the hemodynamic physiology and gas exchange effects during hyperbaric air and HBO(2) exposure, arterial and pulmonary arterial (PA) catheter data, including blood gas values during hyperbaric air and HBO(2) exposure of normal humans, have not been reported. We exposed 10 healthy volunteers instrumented with arterial and PA catheters to air at 0.85, 3.0, 2.5, 2.0, 1.3 (decompression stop), 1.12 (decompression stop), and 0.85 atm abs (our altitude) and then at identical pressures breathing O(2) followed by atmospheric pressure air while we measured arterial and PA pressures (PAP), cardiac output (Q), and blood gas measurements from both arterial and PA catheters. Although hemodynamic changes occurred during exposure to both hyperbaric air and HBO(2), we observed a greater magnitude of change under HBO(2) conditions: heart rate changes ranged from -9 to -19% (air to O(2)), respiratory rate from -12 to -17%, Q from -7 to -18%, PAP from -18 to -19%, pulmonary vascular resistance from -38 to -48%, and right-to-left shunt fraction from -87 to -107%. Mixed venous CO(2) fell 8% from baseline during HBO(2) despite mixed venous O(2) tensions of several hundred Torr. The stroke volume, O(2) delivery, and O(2) consumption did not change across exposures. The arterial and mixed venous partial pressures of O(2) and contents were elevated, as predicted. O(2) extraction increased 37% during HBO(2).