Validity of CO2-rebreathing cardiac output during rest and exercise in young adults

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Abstract
BEEKMAN, ROBERT H., VICTOR KATCH, CHARLES MARKS, and ALBERT P. ROCCHINI. Validity of CO2-rebreathing cardiac output during rest and exercise in young adults. Med. Sci. Sports Exerc., Vol. 16, No. 3, pp. 306–310, 1984. To validate the CO2-rebreathing method (Defare's method) for estimating cardiac output in children and young adults, measurements were compared to thermodilution (TDCO) cardiac output in 16 subjects (age 7–19 yr) with congenital heart disease. Data were collected at rest (N=11) and during 4-min stages of supine bicycle exercise (N=13). Estimated arterial-venous (V̄-a)CO2 content differences related linearly to the measured CO2 content differences (Y=0.29X + 2.47, r=0.65, P2 difference correction for all patients (N=16), the correlation between CO2-rebreathing cardiac output and the TDCO was r=0.87 (SEE= · 1.8 1·min-1). The correlation was higher for exercise (r=0.81) than for rest (r=0.65). We conclude that the CO2-rebreathing method, with a (V̄-a)CO2 content difference adjustment, is a simple, noninvasive technique providing estimates of cardiac output in children and young adults with congenital heart disease. Individual estimates should be treated with caution, especially when used for clinical evaluations.