Cardiac output estimated noninvasively from oxygen uptake during exercise

Stringer, William W., James E. Hansen, and K. Wasserman.Cardiac output estimated noninvasively from oxygen uptake during exercise. J. Appl. Physiol. 82(3): 908–912, 1997.—Because gas-exchange measurements during cardiopulmonary exercise testing allow noninvasive measurement of oxygen uptake (V˙o 2 ), which is equal to cardiac output (CO) × arteriovenous oxygen content difference C(a-[Formula: see text)], CO and stroke volume could theoretically be estimated if the C(a-Formula: see text) increased in a predictable fashion as a function of %maximumV˙o 2 (V˙o 2 max ) during exercise. To investigate the behavior of C(a-Formula: see text) 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 for blood gases (pH, Formula: see text,Formula: see text) and oxyhemoglobin and hemoglobin concentration with a CO-oximeter. The C(a-Formula: see text) (ml/100 ml) could be estimated with a linear regression C(a-[Formula: see text) = 5.72 + 0.105 × %V˙o 2 max ; r = 0.94]. The CO estimated from the C(a-Formula: see text) by using the above linear regression was well correlated with the CO determined by the direct Fick method ( r = 0.96). The coefficient of variation of the estimated CO was small (7–9%) between the lactic acidosis threshold and peakV˙o 2 . The behavior of C(a-Formula: see text), as related to peakV˙o 2 , was similar regardless of cardiac function compared with similar measurements from studies in the literature performed in normal and congestive heart failure patients. In summary, CO and stroke volume can be estimated during progressive work rate exercise testing from measuredV˙o 2 (in normal subjects and patients with congestive heart failure), and the resultant linear regression equation provides a good estimate of C(a-Formula: see text).