title: Prolonged recovery of cardiac output after maximal exercise in patients with chronic heart failure.
abstract: OBJECTIVE
  The aim of this study was to characterize the kinetics of cardiac output during recovery from maximal exercise in patients with chronic heart failure (CHF).
  
  
  BACKGROUND
  Recent studies have shown that oxygen uptake kinetics during recovery from exercise are delayed in patients with CHF. However, the kinetics of cardiac output during recovery from maximal exercise in CHF has not been examined.
  
  
  METHODS
  Thirty patients with CHF performed maximal upright ergometer exercise with respiratory gas analysis. Kinetics of oxygen uptake (VO2) and carbon dioxide output (VCO2) during recovery were characterized by T1/2, the time to reach 50% of the peak values. Cardiac output was measured at 1-min intervals during exercise and recovery. Kinetics of cardiac output during recovery were characterized by the ratios of cardiac output during the first 4 min of recovery to cardiac output at peak exercise. Overshoot of cardiac output was defined as a further increase in cardiac output at 1 min of recovery above the cardiac output at peak exercise.
  
  
  RESULTS
  Both T1/2 VO2 and T1/2 VCO2 increased as CHF worsened. The ratios of cardiac output during recovery to cardiac output at peak exercise were significantly correlated with T1/2 VO2 (r = 0.47 to 0.62, p < 0.05) and T1/2 VCO2 (r = 0.40 to 0.70, p < 0.05). There was a negative correlation between cardiac index at peak exercise and both T1/2 VO2 (r = -0.65, p < 0.001) and T1/2 VCO2 (r = -0.60, p < 0.001). Overshoot of cardiac output was recognized in 11 of 30 patients. Cardiac index at peak exercise was significantly lower in patients with overshoot (4.5 +/- 0.9 L/min/m2) than in those without overshoot (6.1 +/- 2.1 L/min/m2, p < 0.05). However, because of a continued increase in cardiac output at 1 min of recovery in patients with overshoot, there were no differences in cardiac index after the first minute of recovery. Heart rate at peak exercise and recovery of heart rate did not differ between these groups. Overshoot of cardiac output was caused by a rebound increase in stroke volume which was due to a reduction in systemic vascular resistance.
  
  
  CONCLUSIONS
  Prolonged kinetics of VO2 or VCO2 during recovery from maximal exercise represent impairment of circulatory response to exercise and delayed recovery of cardiac output after exercise. Overshoot of cardiac output at 1 min of recovery was characteristic of severe CHF with poor cardiac output response to exercise.
authors.affiliation: Department of Internal Medicine, Niigata Prefectural Shibata Hospital, Shibata City, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tanabe
authors.forename: M
authors.initials: M
authors.lastname: Takahashi
authors.forename: Y
authors.initials: Y
authors.lastname: Hosaka
authors.forename: M
authors.initials: M
authors.lastname: Ito
authors.forename: E
authors.initials: E
authors.lastname: Ito
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000704:Analysis of Variance; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output; D002908:Chronic Disease; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006333:Heart Failure / Q000145:classification / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology*; D006706:Homeostasis; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D012146:Rest; D012720:Severity of Illness Index; D013318:Stroke Volume; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen