One- and three-minute exercise response in coronary artery disease.

Treadmill exercise responses of oxygen uptake (VO2), CO2 production (VCO2), and venoarterial CO2 difference (Cv-Ca), measured by CO2 rebreathing (Defares technique) at 1 and 3 min of exercise, were studied in two separate series of control (apparently healthy) and coronary artery disease (CAD) subjects. In the 1-min series there were 21 controls and 15 CAD subjects. In the 3-min series there were 21 controls and 18 CAD subjects. All were males, ages 30--60 yr, and the CAD subjects had histories of myocardial infarction. In both series VO2 at 1 min and power requirement (P ) = 1,000 (VO2-1-1,000) was estimated where P =weight (kg) X grade (fractional) X walking speed (m/min). In the 1-min series (P = 1,000) all measurements were made at 45--60 s in separate test runs. In the 3-min series P was 750 kg.m/min, VCO2 and VO2 were measured at 2.5--3 min exercise, and Cv-Ca was measured at 3--3.25 min in the same test run. Data indicate that the average cardiac output (Q) for control subjects was 15 l/min in both series with lower values for CAD subjects. At 1 min reduced Q was accompanied by reduced VO2 or VCO2 and increased Cv-Ca, whereas at 3 min reduced Q was accompanied by increased Cv-Ca.