Arterial and pulmonaryarterial hemodynamics and oxygen delivery/extraction in normal humansexposed to hyperbaric air and oxygen. J Appl Physiol 107: 336–345, 2009.First published April 30, 2009; doi:10.1152/japplphysiol.91012.2008.—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 (Q ̇ ), 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%, Q ̇ from 7 to 18%, PAP from 18 to 19%,pulmonary vascular resistance from 38 to 48%, and right-to-leftshunt fraction from 87 to 107%. Mixed venous CO2 fell 8% frombaseline during HBO2 despite mixed venous O2 tensions of severalhundred Torr. The stroke volume, O2 delivery, and O2 consumptiondid not change across exposures. The arterial and mixed venouspartial pressures of O2 and contents were elevated, as predicted. O2extraction increased 37% during HBO2.