Cardiovascular neuroregulation during acute exposure to 40, 70, and 100% oxygen at sea level

Humans encounter increased partial pressures of inspired oxygen in some kinds of diving as well as during use of hyperoxic mixtures to shorten decompression times and hyperbaric oxygen therapy for decompression sickness or other clinical conditions. Although it is known that hyperoxia may affect cardiovascular regulation, such effects are generally obscured by stress and the diving reflex. In this study, we evaluated cardiovascular neuroregulation for various levels of hyperoxia in a laboratory setting.

There were 10 healthy adults who were exposed to 21, 40, 70, and 100% oxygen administered via mask as a series of stepwise increases. Subjects breathed at a fixed respiratory rate of 15 breaths x min(-1) while their heart rate (HR) and blood pressure (BP) were measured continuously over 5-min intervals.

HR decreased with increasing fraction of inspired oxygen (FIO2) (21%: 65 +/- 9, 40%: 63 +/- 9, 70%: 61 +/- 8, 100%: 60 +/- 8 bpm) and the high-frequency power of HR variability (an index of cardiac parasympathetic activity) increased as FIO2 rose (21%: 773 +/- 565, 40%: 880 +/- 590, 70%: 966 +/- 681, 100%: 1114 +/- 715 ms2); both changes were significant at the 70% and 100% oxygen levels. The low-frequency power of systolic BP variability (an index of vasomotor sympathetic activity) did not change. Low- and high-frequency transfer function gains (indices of arterial-cardiac baroreflex function) increased with FIO2.

Parasympathetic activity and arterial-cardiac baroreflex function increased with hyperoxia in a dose-dependent manner. This increase may help reduce the likelihood of arrhythmias during diving.