Cardiac output estimated noninvasively from oxygen uptake during exercise

Abstract

Because gas-exchange measurements during cardiopulmonary exercise testing allow noninvasive measurement of oxygen uptake (Vo2), which is equal to cardiac output (CO) x arteriovenous oxygen content difference [C(a-vDo2),] CO and stroke volume could theoretically be estimated if the C(a-vDo2) increased in a predictable fashion as a function of % maximum Vo2 (Vo2max) during exercise. To investigate the behavior of C(a-vDo2) 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, Pco2, Po2) and oxyhemoglobin and hemoglobin concentration with a CO-oximeter. The C(a-vDo2) (ml/100 ml) could be estimated with a linear regression [C(a-vDo2) = 5.72 + 0.105 x % Vo2max; r = 0.94]. The CO estimated from the C(a-vDo2) 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 peak Vo2. The behavior of C(a-vDo2), as related to peak Vo2, 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 measured Vo2 (in normal subjects and patients with congestive heart failure), and the resultant linear regression equation provides a good estimate of C(a-vDo2).

Oxygen Uptake Efficiency Plateau Best Predicts Early Death in Heart Failure

“…Logically, by Fick's principle, 26,[36][37][38] the ratio of oxygen uptake to ventilation (ie, OUE 5 o 2 / e ), should evaluate cardiovascular performance, as it is dependent on three factors: cardiac output, arterialmixed venous oxygen content difference, and lung ventilation. 26,[36][37][38] The OUEP tended to be higher in healthier individuals.…”

“…26,[36][37][38] The OUEP tended to be higher in healthier individuals. 24 For reasons that may not be intuitively obvious, in both normal subjects 24 and patients with HF, the OUE was not highest at rest or at maximal exercise, but during moderate exercise ( Fig 1 ).…”

Exercise intolerance in chronic heart failure: mechanisms and therapies. Part I

“…where (A -V), O 2 difference is arterio-venous O 2 difference, which is usually similar between normal individuals and CHF patients [5]. Thus, exercise intolerance is mainly related to heart function and its chronotropic response, both altered in CHF.…”

The Role of Exercise Testing in the Modern Management of Pulmonary Arterial Hypertension

“…The estimated range of normality for mPAP change on exercise is 0.5-3.0 mmHg.min.L −1 [20] whereas the normal range for PAOP change is less certain, one estimate being 0.3-1.93 mmHg.min.L −1 [19]. During supine exercise PVR falls slightly [21,22] and S v O2 falls from 75% at rest to 25% at maximal exercise [23]. By contrast in PAH there is a very steep rise in mPAP over a much more limited CO response.…”