Non-invasive measurement of stroke volume during exercise in heart failure patients

The objective of the present study was to determine the variability of the arterio-venous O-2 concentration difference [C(a-v)O-2] at anaerobic threshold and at peak oxygen uptake ((V)overdot O-2) during a progressively increasing cycle ergometer exercise test, with the purpose of assessing the possible error in estimating stroke volume from measurements of (V)overdot O-2 alone. We sampled mixed venous and systemic arterial blood every I min during a progressively increasing cycle ergometer exercise test and measured, in each blood sample, haemoglobin concentration and blood gas data. Ventilation, (V)overdot O-2 and CO2 uptake were also measured continuously. We studied 40 patients with normal haemoglobin concentrations and with stable heart failure due to ischaemic or idiopathic cardiomyopathy. Mean values (+/-S.D.) for C(a-v)O-2 were 7.8+/-2.6, 13.0 +/- 2.4 and 15.0 +/- 2.7 ml/100 ml at rest, anaerobic threshold and peak (V)overdot O-2 respectively. The patients with heart failure were divided into classes according to their peak Vet. Classes A, B and C contained patients with peak (V)overdot O-2 values of > 20, 15-20 and 10-15 ml . min(-1) . kg(-1) respectively. Ar anaerobic threshold, C(a-v)O-2 was 12.3 +/- 1.3, 13.1 +/- 2.7 and 13.5 +/- 2.6 ml/100 ml for classes A, B and C respectively (class A significantly different from classes B and C; P < 0.05). At peak exercise C(a-v)O-2 was 13.6 +/- 1.4, 15.6 +/- 2.5 and 15.4 +/- 3.2 ml/100 ml for classes A, B and C respectively (class A significantly different from classes B and C; P < 0.05). Stroke volume was estimated for each subject using the mean values of the measured C(a-v)O-2 in each functional class and individual values of (V)overdot O-2 and heart rare using the Fick formulation. The average difference between the stroke volume estimated from mean C(a-v)oz and that obtained using the patient's actual C(a-v)O-2 value was 9.2+/-9.7, 1.0+/-8.8 and -0.2+/-6.1 ml at anaerobic threshold, and - 1.9+/-11.3, 0.9+/-10.0 and -2.3+/-8.5 ml at peak exercise, in classes A, B and C respectively. Among the various classes, the most precise estimation of stroke volume was observed for class C patients. We conclude that stroke volume during exercise can be estimated with the accuracy needed for most purposes from measurement of (V)overdot O-2 at the anaerobic threshold and at peak exercise, and from population-estimated mean values for C(a-v)O-2, in heart failure patients.