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

Abstract

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.

Figure 1

Example of calculation of the time constant (TC) value for the first 2 postexercise minutes. TC expresses the time (in sec) after which VO₂ has declined 63% below the peak value.

Figure 2

Schematic presentation of the mean VO₂ recovery curves for the four groups.

Figure 3

Examples of VO₂ and HR recovery after exercise with the corresponding time constant in a normal individual (a), (b) and in a patient with heart failure (c), (d).