Readjustments in cardiac output and gas exchange during onset of exercise and recovery.

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Abstract
Muscular exercise is characterized by an increase in O2 uptake and CO2 output, and by increases in ventilation and cardiac output. This study was conducted in order to determine the rate at which these 4 functions readjust during onset of exercise and recovery and how the arterial and venous blood gases are affected. The subjects exercised on a treadmill and the various variables were measured at frequent intervals, the cardiac output being determined by a modification of Kim''s technique. When expressed in relation to the over-all steady-state change, the rate of change of the 4 functions considered (VCO2 [postabsorption body CO2 consumption], VO2 [postabsorption body O2 consumption], VE [ventilation], and Q [cardiac output]) was found to be independent of the work load. Changes in VO2 are more rapid than changes in VCO2. The changes in VE are rapid at first, exceeding the rate of change in gas exchange, and later parallel the changes in VCO2. Similarly, Q exhibits a rapid initial change which decreases later. Since the initial phase is more rapid than the metabolic changes, the readjustment in cardiac output at the onset of excercise must be under neurogenic influence.