Body carbon dioxide storage capacity in exercise

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Abstract
Body CO2 storage capacity was measured in 9 subjects at 2 levels of exercise, approximating 30 and 60% VO2 max [maximal O2 consumption], by measuring the excess CO2 output associated with hyperventilation at constant end-tidal PCO2 [partial pressure of CO2], and the change in mixed venous PCO2 (P.hivin.vCO2) measured by rebreathing. CO2 output was measured during 20-s periods and monitored throughout the procedure; hyperventilation was continued until CO2 output had returned to control values. Washout of CO2 was more rapid than previously found at rest, 90% of the change following an increase in ventilation occurring within 4 min. CO2 storage capacity was 1.83 .+-. 0.552 (SD) ml .cntdot. kg-1 .cntdot. Torr-1 at the lower power output and 1.19 .+-. 0.490 ml .cntdot. kg-1 .cntdot. Torr-1 at the higher power output. The CO2 storage capacity was inversely related to P.hivin.vCO2. The body''s capacity to store CO2 decreases with increasing P.hivin.vCO2; this may be 1 factor leading to the progressive increase in pulmonary CO2 output at high levels of exercise.