Evaluation of autonomic function underlying slow postexercise heart rate recovery.
The reduction in heart rate (HR) during the first minute of recovery immediately after a graded maximal exercise stress test (GXT) has recently been found to be a powerful and independent predictor of cardiovascular and all-cause mortality. Reduced vagal activity has been postulated as the cause, but this has not been proven in a population with slow HR recovery (HRR).


OBJECTIVE
To investigate autonomic contributions to HRR using time-frequency analysis in a group of individuals demonstrating slow HRR.


METHODS
HRR was defined as the difference in HR between peak exercise and 1 min later; a value < or = 18 bpm was set as threshold and considered abnormal. A modified continuous wavelet transform (CWT) was used to perform time-dependent spectral analysis during the baseline steady state and the following non-steady-state conditions created by GXT. This method provides dynamic measures of low-frequency (LF) and high-frequency (HF) peaks associated with autonomic activity. Individuals (N = 20) with a previous slow HRR underwent a second GXT within 3 months after their initial test. An additional eight subjects whose first GXT disclosed normal HRR were taken as a control group.


RESULTS
Seven of 20 subjects demonstrated slow HRR (14 +/- 5 bpm) on the repeat test, and 13 subjects displayed normal HRR (29 +/- 5 bpm). Subjects with slow HRR in both GXT displayed significantly (P < 0.05) lower HF and LF fluctuations during recovery than those with normal HRR.


CONCLUSIONS
Attenuated HRR after GXT, assessed by CWT, is indeed associated with abnormal vagal reactivation and prolonged sympathetic stimulation after termination of maximal exercise.
Davrath
Linda R
LR
Sackler Faculty of Exact Sciences, Abramson Center for Medical Physics, Tel Aviv University, Tel Aviv, Israel. lindad@post.tau.ac.il
Akselrod
Solange
S
Pinhas
Itzik
I
Toledo
Eran
E
Beck
Amit
A
Elian
Dan
D
Scheinowitz
Mickey
M
D001341:Autonomic Nervous System / Q000502:physiology*; D016022:Case-Control Studies; D005080:Exercise Test; D005260:Female; D006321:Heart / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020127:Recovery of Function / Q000502:physiology*; D013997:Time Factors; D016277:Ventricular Function, Left / Q000502:physiology