THE PHYSIOLOGICAL MEANING OF THE MAXIMAL OXYGEN INTAKE TEST1

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Abstract
Maximal O2 intake was determined in 65 normal men, aged 20 to 65, using a treadmill. In 15 normal individuals, O2 intake and cardiac output (dye dilution method) were measured at rest and at increasing work loads including that producing maximal O2 intake. Pulse and respiratory rates were also determined. Blood samples were drawn from brachial artery, brachial vein, and femoral vein during each work load for determination of O2 content and capacity, pO2 (polarographic), CO2 content, pH, and pCO2 (calculated). Oxygen intake increased 9.5 times (from rest to maximal value). Cardiac output increased 4.3 times and AV oxygen difference 2.2 times. Pulse rate and mean cardiac stroke volume were both approximately doubled. Arterial pO2 was 87+9 during rest and 88 [plus or minus] 12 during heavy exercise. A slight drop in arterial O2 saturation was attributable to arterial pH changes (7.40 [plus or minus] .04 at rest and 7.19 [plus or minus].09 during exercise). pO2 of venous blood from both sites was maintained during exercise in spite of a marked decrease in venous saturation. In 6 subjects, who performed loads beyond that producing maximal O2 intake, cardiac output decreased. The data show that both cardiac output capacity and the extent to which venous O2 content can fall are determinants of maximal O2 intake.