Abstract
Cardiac output (Q) was measured by the CO2 rebreathing method in 10 boys and 9 girls. They performed cycle ergometer exercises at 300 and 450kgm/min in ambient temperatures kept at 20, 30, and 40°C. For a given oxygen uptake (Vo2), stroke volume (SV) tended to be reduced and heart rate (HR) increased in a 40°C environment in both sexes. Accordingly, Q at 40°C was maintained at a level similar to that in cooler conditions. A lower HR and a higher SV at a given Vo2 were shown in boys than in girls. The regression equation of Q on Vo2 in boys was found to be similar to that in girls. The values of Q in relation to Vo2 in the children studied were compared with those in children and adults who had been previously studied. The children in the present study were found to have a Q response that represented roughly an average of those of children described in the literature cited, and to have a lower Q as compared with most adults.
