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 less than 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.
Itoh
H
H
Cardiovascular Institute Hospital, Tokyo, Japan.
Nakamura
M
M
Ikeda
C
C
Yanagisawa
E
E
Hatogai
F
F
Iwadare
M
M
Taniguchi
K
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D002302:Cardiac Output; D005080:Exercise Test; D005260:Female; D006333:Heart Failure / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D010100:Oxygen / Q000378:metabolism*; D005082:Physical Exertion; D012044:Regression Analysis
D010100:Oxygen; D009638:Norepinephrine