Oxygen Kinetics and Heart Rate Response during Early Recovery from Exercise in Patients with Heart Failure

Background. The purpose of this study was to assess the post-exercise O-2 uptake and heart rate response in patients with heart failure (HF) in comparison to healthy individuals. Methods and Results. Exercise testing of all subjects was conducted according to the RITE-protocol. The study subjects were classified according to their peak oxygen uptake (peak VO2) in four groups: healthy individuals with a peak VO2 > 22 mL/kg/min (group 1, n: 50), and patients with HF and a peak VO2 of 18-22 mL/kg/min, (group 2, n: 48), 14-18 mL/kg/min (group 3, n: 57), and < 14 mL/kg/min (group 4, n: 31). Both peak VO2 and HR declined more slowly in the patients with HF than in the normal subjects. Recovery of VO2 and HR followed monoexponential kinetics in the early postrecovery phase. This enabled the determination of a time constant for both HR and VO2 (TC VO2 and TC HR). From group 1 to 4 there was a prolongation of the time constant for VO2 and HR: TC VO2 (group 1: 110 +/- 34, group 2: 197 +/- 43, group 3: 238 +/- 80, and group 4: 278 +/- 50 sec), and TC HR (group 1: 148 +/- 82, group 2: 290 +/- 65, group 3: 320 +/- 58, and group 4: 376 +/- 55 sec). Conclusion. The rate of decline of VO2 and HR in the early post-exercise phase is inversely related to the peak VO2. The time constant for oxygen uptake (TC VO2) and heart rate (TC HR) might prove a useful parameter for more precise monitoring and grading of HF.