CARDIAC-OUTPUT ESTIMATED NONINVASIVELY FROM OXYGEN-UPTAKE DURING EXERCISE

Because gas-exchange measurements during cardiopulmonary exercise test ing allow noninvasive measurement of oxygen uptake (VO2), which is equ al to cardiac output (CO) X arteriovenous oxygen content difference [C (a-vD(O2))], CO and stroke volume could theoretically be estimated if the C(a-vD(O2)) increased in a predictable fashion as a function of %m aximum VO2 (VO2max) during exercise. To investigate the behavior of C( a-vDO(2)) during progressively increasing ramp pattern cycle ergometry exercise, 5 healthy subjects performed 10 studies to exhaustion while arterial and mixed venous blood were sampled. Samples were analyzed f or blood gases (pH, PCO2, P-O2) and oxyhemoglobin and hemoglobin conce ntration with a CO-oximeter. The C(a-vD(O2)) (ml/100 ml) could be esti mated with a linear regression [C(a-vD(o2)) = 5.72 +/- 0.105 X %VO2max ; r = 0.94]. The CO estimated from the C(a-vD(O2)) by using the above Linear regression was well correlated with the CO determined by the di rect Fick method (r = 0.96). The coefficient of variation of the estim ated CO was small (7-9%) between the lactic acidosis threshold and pea k VO2. The behavior of C(a-vD(O2)), as related to peak VO2, was simila r regardless of cardiac function compared with similar measurements fr om studies in the literature performed in normal and congestive heart failure patients. In summary, CO and stroke volume can be estimated du ring progressive work rate exercise testing from measured VO2 (in norm al subjects and patients with congestive heart failure), and the resul tant Linear regression equation provides a good estimate of C(a-vD(O2) ).