Aerobic Endurance is Reduced Immediately after Repeated 6‐hr Normoxic and Hyperoxic Dives at 1.35 ATA and Remains Reduced in the Hyperoxic Group 3 Days after the Last Dive

Abstract

Previous measures of aerobic endurance after repeated dives on air and 100% oxygen have shown reductions in performance 24‐hr after surfacing for the hyperoxic group only. The purpose of this study was to determine aerobic endurance immediately after completing repeated (5 consecutive 6‐hr dives with 18‐hr surface intervals; dive week, DW) air and oxygen resting dives and to determine performance recovery 3 days after diving. 15 and 13 healthy men completed the air phase and 100% oxygen phase, respectively (Air/Oxygen: 29±1/31±2 yrs; VO2MAX: 55±3/53±3 ml/kg/min; mean±SD) at 1.35 atmospheres absolute (ATA). Pre‐dive base line measurements of endurance time at 85% of VO2MAX and associated physiological variables were performed a few days prior to the first dive (BL), with post‐dive (PD) and 3‐day post (PD3) recovery endurance measurements performed within two hours of surfacing and 3 days after the fifth dive of the DW. Change in plasma volume (PV) from BL was calculated from changes in hemoglobin and hematocrit (Dill‐Costill equation), both measured before exercise. Heart rate (HR), cardiac output (Q), blood lactate, and Rating of Perceived Exertion (RPE) were measured throughout the run at 85% VO2MAX: during the 5‐min walking warmup,3‐min level run, and every three min during the run at 10% grade untilex haustion. Stroke volume (SV) was calculated as Q/HR. PD PV was consistently reduced compared to BL for both phases (Air: Δ= −10.7%; Oxygen: Δ= −10.7%;p<0.05), but returned to BL levels in both groups by PD3. PD aerobicendurance significantly decreased in comparison to BL for both the Air and Oxygenphases (Air: Δ= −34%; Oxygen: Δ= −36%; p<0.05). Aerobic endurance recoveredfully by PD3 in the Air phase (Δ= −11.9%; p>0.05), but remained reduced in the Oxygen phase (Δ= −31%; p<0.05). Comparison of physiological variables at the run time matching the last data point (exhaustion) for the shortest of the three runs showed that PD HR was significantly higher than at BL for the Air phase as well as compared to Oxygen PD HR (Air PD>BL: Δ= +7%, Air>Oxygen: Δ= +5%; p<0.05). For both groups, PD Q and SV were lower than at BL (Air Q: Δ= −19%, SV: Δ= −25%;Oxygen: Q: Δ= −12%, SV: Δ= −13%; p<0.05), with Air phase Q at PD3 remaining significantly higher than Oxygen (Air>Oxygen: Δ= +20%; p<0.05). PD RPE was higher than BL for both groups (Air: Δ= +13%; Oxygen: Δ= +16%; p<0.05) but remained elevated only for the oxygen group at PD3 (Oxygen: Δ= +19%; p<0.05). Lactate for match time analysis increased in only the oxygen phase PD (Oxygen: Δ=+19%; p<0.05). Previous work has shown that hyperoxia alters vascularfunction and cardiac and baroreflex regulation during exposure. These results demonstrate that some effects of hyperoxic dives persist for up to three days after diving, as indicated by reduced aerobic endurance as well as blunted HR response and suppressed Q compared to the Air group. Although peak HR obtained at exhaustionobtained in the Oxygen group did not change across days, increased lactate and RPE levels after Oxygen dives suggest that subjects were working harder after diving than before to maintain the same workload, despite the return of PV to BL levels. More work is needed to determine the mechanisms of these hyperoxia‐related reductions in performance.Support or Funding InformationOffice of Naval Research (ONR) Award Number N000141612112 and NAVSEA DSBDP N0002416WX02277.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.