O2 pulse slope correlates with stroke volume during exercise in patients with a Fontan circulation

Abstract

BackgroundPeak oxygen pulse (O2pulse=oxygen consumption/heart rate) is calculated by the product of stroke volume (SV) and oxygen extraction. It has been shown to be reduced in patients with a Fontan circulation. However, in the Fontan population, it may be a poor marker of SV. We propose that the slope of the O2pulse curve may be more reflective of SV during exercise.MethodsWe analysed cardiopulmonary exercise test data in 22 subjects with a Fontan circulation (cohort A) and examined the association between peak SV during exercise (aortic flow measured on exercise cardiac MRI), and O2pulse parameters (absolute O2pulse and O2pulse slopes up to anaerobic threshold (AT) and peak exercise). In a separate Fontan cohort (cohort B, n=131), associations between clinical characteristics and O2pulse kinetics were examined.ResultsIn cohort A, peak aortic flow was moderately and significantly associated with O2pulseslopePEAK(r=0.47, p=0.02). However, neither absolute O2pulseATnor O2pulsePEAKwas significantly associated with peak aortic flow. In cohort B, O2pulseslopePEAKand O2pulseslopeATwere not significantly associated with clinical parameters, apart from a weak association with forced vital capacity.ConclusionThe slope of the O2pulse curve to peak exercise may be more reflective of peak SV in the Fontan population than a single peak O2pulse value.