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 VO 2 ) in four groups: healthy individuals with a peak VO 2 >22 mL/kg/min (group 1, n : 50), and patients with HF and a peak VO 2 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 VO 2 and HR declined more slowly in the patients with HF than in the normal subjects. Recovery of VO 2 and HR followed monoexponential kinetics in the early post-recovery phase. This enabled the determination of a time constant for both HR and VO 2 (TC VO 2 and TC HR). From group 1 to 4 there was a prolongation of the time constant for VO 2 and HR: TC VO 2 (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 VO 2 and HR in the early post-exercise phase is inversely related to the peak VO 2 . The time constant for oxygen uptake (TC VO 2 ) and heart rate (TC HR) might prove a useful parameter for more precise monitoring and grading of HF.