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

Abstract

Weaver LK, Howe S, Snow GL, Deru K. Arterial and pulmonary arterial hemodynamics and oxygen delivery/extraction in normal humans exposed 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 Ϫ9 to Ϫ19% (air to O2), respiratory rate from Ϫ12 to Ϫ17%, Q from Ϫ7 to Ϫ18%, PAP from Ϫ18 to Ϫ19%, pulmonary vascular resistance from Ϫ38 to Ϫ48%, and right-to-left shunt fraction from Ϫ87 to Ϫ107%. 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. hyperbaric oxygen; pulmonary arterial catheter; cardiac output; oxygen extraction THOUSANDS OF PATIENTS have been treated with hyperbaric oxygen (HBO 2 ); however, the precise arterial and pulmonary arterial (PA) hemodynamic and gas exchange responses that occur during HBO 2 are not clearly known. Determining precise hemodynamic and gas exchange information requires the subject or patient to be instrumented with arterial and PA (SwanGanz) catheters, permitting measurement of intravascular pressures and blood gases, and PA catheter data collected in normal humans exposed to HBO 2 has been reported only once (24).It has long been established that heart rate (HR) falls during HBO 2 (3). Forty years ago, investigators reported that this reduction in HR was associated with decreased cardiac output (Q ) (48), an observation supported by subsequent research (Table 1) (21,24,27,29,48). Generally accepted hemodynamic effects of HBO 2 now "include mild bradycardia, leading to a proportional decline in Q and a small increase in systemic vascular resistance" (28).As (43), possibly due to high O 2 concentrations reducing myocardial relaxation factor (nitric oxide), thereby making the heart stiffer (23), or by an increase in afterload from i...

Hyperbaric hyperoxia reduces exercising forearm blood flow in humans

“…These findings are in contrast to previous reports that suggest resting cardiac output is reduced during hyperbaric hyperoxia (17,20,30,33). This discrepancy may be explained by the stroke volume being derived from the beat-to-beat brachial arterial pulse pressure wave using model flow analysis in the current study, whereas other studies have relied on thermal and indicator dilution methods.…”

“…Therefore, our estimated increase (ϳ25-30%) in arterial O 2 content during hyperoxia is based on calculated values of arterial PO 2 as described in METHODS. The estimated O 2 tensions from the current study are similar to those previously reported using direct measurements of Pa O 2 (i.e., micro-O 2 electrode or arterial blood sample) in subjects exposed to hyperbaric O 2 (8,19,29,30). Additionally, we were not able to calculate or determine whether O 2 consumption in the active forearm was different between trials.…”

Long-term treatment with hyperbaric air improves hyperlipidemia of db/db mice

“…HBA increases oxygen contents of the blood by about 2.5%, much less than the increase induced by HBO (30). A previous study using microarray analysis of neurons showed that HBA increases the expression levels of more genes than does normobaric oxygen (31).…”

The effect of hyperbaric oxygen preconditioning on heat shock protein 72 expression following in vitro stress in human monocytes

“…Any increase in oxygen within the circulation comes from the increased alveolar partial pressure of oxygen during HBO exposure (Weaver et al 2009) and no changes in rates of oxygen delivery and consumption have been reported after HBO (Weaver et al 2009). Therefore, one could reasonably argue that HBO does not induce a significant stress response within the blood cell population.…”