Oxygen uptake kinetics during low level exercise in patients with heart failure: relation to neurohormones, peak oxygen consumption, and clinical findings

Objective-To investigate whether oxygen uptake ((V) over dot O-2) kinetics during low intensity exercise are related to clinical signs, symptoms, and neurohumoral activation independently of peak oxygen consumption in chronic heart failure. Design-Comparison of (V) over dot O-2 kinetics with peak (V) over dot O-2, neurohormones, and clinical signs of chronic heart failure. Setting-Tertiary care centre. Patients-38 patients with mild to moderate chronic heart failure. Interventions-Treadmill exercise testing with "breath by breath" gas exchan ge monitoring. Measurement of atrial natriuretic factor (ANF), brain natriu retic peptide (BNP), and noradrenaline. Assessment of clinical findings by questionnaire, Main outcome measures-O-2 kinetics were defined as O-2 deficit (time [rest to steady state] x Delta(V) over dot o(2) - Sigma(V) over dot O-2 [rest to steady state]; normalised to body weight) and mean response time of oxygen consumption (MRT; O-2 deficit/Delta(V) over dot O-2). Results-(V) over dot O-2 kinetics were weakly to moderately correlated to t he peak (V) over dot O-2 (O-2 deficit, r = -0.37, p < 0.05; MRT, r = -0.49, p < 0.001). Natriuretic peptides were more closely correlated with MRT (AN F, 0.58; BNP, r = 0.53, p < 0.001) than with O-2 deficit (ANF, r = 0.48, p = 0.001; BNP, 0.37, p < 0.01) or peak (V) over dot O-2 (ANF, -0.40; BNP, r = -0.31, p < 0.05). Noradrenaline was correlated with MRT (r = 0.33, p < 0. 05) and O-2 deficit (r = 0.39, p < 0.01) but not with peak (V) over dot O-2 (v = -0.20, NS). Symptoms of chronic heart failure were correlated with al l indices of oxygen consumption (MRT, r = 0.47, p < 0.01; O-2 deficit, r = 0.39, p < 0.01; peak ire,, r = -0.48, p < 0.01). Multivariate analysis show ed that the correlation of (V) over dot O-2 kinetics with neurohormones and symptoms of chronic heart failure was independent of peak (V) over dot O-2 and other variables. Conclusions-Oxygen kinetics during low intensity exercise may provide addit ional information over peak (V) over dot O-2 in patients with chronic heart failure, given the better correlation with neurohormones which represent a n index of homeostasis of the cardiovascular system.