Hana kai ii: a 17-day dry saturation dive at 18.6 ATA. V. Maximal oxygen uptake.

Cardiorespiratory responses of four men to submaximal and maximal cycling exercise were observed during 17 days at 18.6 ATA. Inspired gas at pressure consisted of hyperoxic (PO2 = 232 mmHg) and normoxic (PO2 = 159 mmHg) helium mixtures with relative gas densities of 3.8 and 2.8, respectively. The average of pre- and postdive VO2max (1 ATA air), which were not significantly different, was 3.10 liters - min-1. During 5 min of submaximal exercise at 50% of VO2max, no significant difference in work rate, VO2, VCO2, VE, respiratory rate, heart rate (HR), stroke volume, blood pressures, or rectal temperature was noted at 18.6 ATA compared to 1 ATA with either gas mixture. Submaximal HR tended to decrease by 5 to 10 beats - min-1 at pressure, and in hyperoxia the VO2/HR ratio was significantly higher. Maximal exercise was performed to exhaustion at work rates requiring about 120% of VO2max. Significant increased in VO2max of 0.10 liter - min-1 (3%) and in endurance time of 2 min (48%) were found during hyperoxic gas breathing, whereas normoxic values at 18.6 ATA were similar to those at 1 ATA. Significant reductions in maximal HR of 8 beats - min-1 (4%) were observed with both gas mixtures at pressure, and VE was significantly decreased by 36 liters - min-1 (26%) in hyperoxia and 29 liters - min-1 (21%) in normoxia. No change was found in the calculated cardiac output. Maximal voluntary ventilation, which was measured only for the hyperoxic gas, fell significantly by 80 liters - min-1 (40%). Results indicate that aerobic power and endurance performance were affected by oxygen pressure. Normoxic work capacity, however, was not decreased at 18.6 ATA, despite marked reductions in HR and VE.