Gas exchange analysis of immediate CO2 storage at onset of exercise

The immediate storage of CO2 at the onset of exercise was estimated in 5 subjects as the difference between measured and predicted CO2 production at work rates of 33, 53 and 75% VO2max. Three time varying models of respiratory exchange ratio (RER) were used to obtain an expected range of predicted CO2 production. Calculated CO2 storage in the transition from rest to 33% VO2max ranged from 0.33 to 0.38 ml X kg-1 X torr-1; from 33 to 53% VO2max, corresponding values were -0.04 to 0.14 ml X kg-1 X torr-1; and, from 53 to 75% VO2max, values ranged from -0.25 to 0.16 ml X kg-1 X torr-1. In two models, CO2 storage decreased significantly at the highest work rate. Estimates of CO2 storage by hyperventilation in the steady state of exercise yielded significantly greater storage. It was concluded that immediate CO2 storage at the onset of exercise was less than hyperventilation estimates, and that it tended to decrease with metabolic acidosis.