Determination of cardiac output by the CO2 - rebreathing method in fifteen-year-old boys subjected to graduated loading.

The dynamics of cardiac output changes were studied in 23 15-year-old boys subjected to graduated loading up to maximum on an bicycle ergometer and relationships between cardiac output and other indexes of cardiorespiratory functions were determined. The correlation between cardiac output (Q in 1/min) and oxygen consumption (VO2 in 1/min) was Q = 6.84 + 5.64. VO2. CO2-rebreathing was found to be a suitable non-invasive method for determining cardiac output in loading tests in adolescents. Maximum cardiac output correlated with maximum oxygen consumption, maximum pulmonary ventilation, body weight, lean body mass and physical working capacity W 170 and did not correlate with systolic volume, the arteriovenous oxygen difference, the pulse rate and ballistocardiographic force. The absence of any statistically significant differences between the various functional indexes of the physical fitness of trained and untrained boys indicates that training was not very effective.