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 (HBO₂) is used therapeutically frequently. Although much is understood about the hemodynamic physiology and gas exchange effects during hyperbaric air and HBO₂ exposure, arterial and pulmonary arterial (PA) catheter data, including blood gas values during hyperbaric air and HBO₂ 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 O₂ followed by atmospheric pressure air while we measured arterial and PA pressures (PAP), cardiac output (Q̇), and blood gas measurements from both arterial and PA catheters. Although hemodynamic changes occurred during exposure to both hyperbaric air and HBO₂, we observed a greater magnitude of change under HBO₂ conditions: heart rate changes ranged from −9 to −19% (air to O₂), respiratory rate from −12 to −17%, Q̇ 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 CO₂ fell 8% from baseline during HBO₂ despite mixed venous O₂ tensions of several hundred Torr. The stroke volume, O₂ delivery, and O₂ consumption did not change across exposures. The arterial and mixed venous partial pressures of O₂ and contents were elevated, as predicted. O₂ extraction increased 37% during HBO₂.