CHANGES IN OXYGEN UPTAKE-WORK RATE RELATIONSHIP AS A COMPENSATORY MECHANISM IN PATIENTS WITH HEART-FAILURE

To assess the compensatory change in oxygen uptake (VO2) kinetics during exercise in patients with heart failure, we performed cardiopulmonary exercise testing using a cycle ergometer in 29 cardiac patients and 18 normal subjects. The work rate increased linearly (1w/6sec) after a 4 min, 20w warm-up. The ratio of increase in VO2 to increase in work rate (DELTA-VO2/DELTA-WR) was determined by linear regression of VO2 Plots. Cardiac output by dye dilution method and plasma norepinephrine concentration (NE) were measured at rest and 20w warm-UP. VO2 at rest and at 20w warm-up and DELTA-VO2/DELTA-WR decreased significantly with increasing severity in NYHA functional classification. DELTA-VO2/DELTA-WR showed significant negative correlation to the difference in NE levels at rest and at 20w (r= -0.69, p < 0.001). The delta values of arteriovenous O2 content difference, calculated using Fick's principle, and cardiac index from rest to 20w warm-up failed to show significant relationship to DELTA-VO2/DELTA-WR. These results suggest that the decrease in VO2 requirement in heart failure patients is due probably to blood redistribution during exercise as a compensatory mechanism for exercise intolerance.