Estimation of oxygen uptake from heart rate response to undersea work

The efficacy of using a diver's heart rate (HR) response to work performed formed in the open sea to estimate the oxygen uptake (VO2) and work stress by general and depth-specific regression equations was examined in six scuba divers. A diver-carried data recording system and an underwater gas sampler were used to obtain measures of physiological responses to work in the ocean. The HR and VO2 were measured during dry cycling at 1 ATA, and during moderate to very heavy work fin-swimming against an ergometer at 2, 3, and 4 ATA. Underwater VO2 and HR at 2-4 ATA ranged from 1.41 to 3.89 liters/min (39%-89% VO2max observed on land) and 105-180 beats/min, respectively. Individual data points at three work levels at 1-4 ATA were used to compute correlation coefficients (r) and regression equations. Only one significant difference in regression slopes was found (1 ATA vs. 4 ATA), but large differences in intercept were observed in each comparison. From 1 ATA to 4 ATA r decreased from 0.78 to 0.53 while the standard error of VO2 estimated from HR (Syx) increased from 0.229 to 0.582 liters O2. The regression equation for dry exercise (1 ATA) underestimated VO2 over most of the work range by 0.4 to 0.9 liters/min or 11% to 25% of VO2max. The accuracy of estimating VO2 from cardiac response by general (1 ATA) or depth-specific regression equations is insufficient to justify their use in research or diver monitoring systems. Attempts to estimate VO2 from pulmonary ventilation (VE) gave similar results with more differences between slopes among the conditions. These observations and those of other investigators support the idea that underwater work loads and stress cannot be estimated or evaluated by simple HR measurements that are made during diving operations and interpreted in terms of sea-level standards.