Accuracy of cardiac output, oxygen uptake, and arteriovenous oxygen difference at rest, during exercise, and after vasodilator therapy in patients with severe, chronic heart failure.

Measurement of cardiac output, arteriovenous oxygen difference, and oxygen uptake in patients with heart failure may be subject to technical and biologic inaccuracies. We measured these 3 variables in 16 patients with chronic heart failure at rest and during exercise. When cardiac output was measured by thermodilution and compared with values calculated by the Fick principle, there was a significant correlation at rest (r = 0.91, p less than 0.001) and at exercise (r = 0.93, p less than 0.001). When the arteriovenous oxygen difference was measured by spectrophotometry of arterial and mixed venous samples and compared with values calculated by the Fick principle, there was a significant correlation at rest (r = 0.80, p less than 0.01) and at exercise (r = 0.76, p less than 0.01). When oxygen uptake was measured from expired gas analysis and compared with values calculated by the Fick principle, there was a significant correlation at rest (r = 0.84, p less than 0.01) and at exercise (r = 0.94, p less than 0.001). In addition, 10 patients received vasodilator treatment which increased cardiac output and decreased the arteriovenous oxygen difference at rest and exercise. There was no significant difference between measured and calculated values for the 3 variables under those additional conditions. It is concluded that despite technical and biologic difficulties, cardiac output, arteriovenous oxygen difference, and oxygen uptake, when calculated from Fick's principle, yield results equivalent to direct measurement.