title: Heart rate response to graded exercise correlates with aerobic and ventilatory capacity in patients with heart failure.
abstract: BACKGROUND
  Autonomic dysfunction and reduced exercise tolerance are typical features of patients with congestive heart failure (CHF). Baro-chemoreflex balance and organ response may have a common role in conditioning exercise tolerance, ventilation, and chronotropic competence in patients with CHF.
  
  
  OBJECTIVE
  We tested the hypothesis that there is a relationship between functional capacity and chronotropic competence to exercise in CHF.
  
  
  METHODS
  In all, 48 stable outpatients with CHF (age 65 +/- 10 years, 41 men, NYHA class 2.1 +/- 0, ejection fraction 31 +/- 7%, peak VO2 16 +/- 4 ml/kg/min) performed cardiopulmonary exercise testing (CPX). Heart rate (HR) response to exercise was assessed by the chronotropic index (CRI). The CRI was calculated by the following formula: CRI = peak HR - rest HR/220 - age - rest HR x 100 (normal value > 80%). The relationship of CRI to peak oxygen consumption (VO2) and ventilation/carbon dioxide production (VE/VCO2) ratio was examined. A group of 33 healthy controls underwent CPX as well.
  
  
  RESULTS
  The CRI correlated directly with peak VO2 (r = 0.638, p < 0.001) and inversely with VE/VCO2 (r = -0.492, p < 0.001) in patients with CHF. A CRI < 78% identified patients with CHF and a peak VO2 < 20 ml/kg/min, area under the receiver operating curve (AUROC): 0.76, 95% confidence interval (CI) 0.60-0.92. A CRI < 74% predicted exercise hyperventilation in CHF (AUROC: 0.71 for VE/VCO2 > 30, 95% CI 0.53-0.88). The CRI was not significantly related either to peak VO2 or to VE/VCO2 in the control group.
  
  
  CONCLUSIONS
  In patients with mild to moderate CHF, CRI correlates with functional capacity. This relationship adds new data on pathophysiologic grounds and supports the routine incorporation of CRI into CPX interpretation.
authors.affiliation: Department of Cardiology, Heart Failure Unit, Rapallo Hospital, Rapallo (Genoa), Italy. avallebona@as14.liguria.it
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vallebona
authors.forename: Guido
authors.initials: G
authors.lastname: Gigli
authors.forename: Sandro
authors.initials: S
authors.lastname: Orlandi
authors.forename: Giorgio
authors.initials: G
authors.lastname: Reggiardo
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D015444:Exercise / Q000502:physiology*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*