Abstract
Cardiac vagal tone (CVT), a key determinant of resting heart rate (HR), is progressively
withdrawn with incremental exercise and nearly abolished at maximal effort. While
maximal HR decreases with age, there remains a large interindividual variability of
results for any given age. In the present study, we hypothesized that CVT does not
contribute to age-independent maximal HR. Data were obtained from 1 000 (39±14 years
old) healthy subjects (719 men) who were not taking medications affecting CVT or maximal
HR performed a clinically normal and truly maximal cardiopulmonary exercise testing.
CVT was estimated using the cardiac vagal index (CVI), a dimensionless ratio obtained
by dividing 2 cardiac cycle durations – end of exercise and pre-exercise -, reflecting
HR increases during a 4-s unloaded cycling test (a vagally-mediated response). Maximal
HR was expressed as % of that predicted by age (208–0.7 × age (years)). Linear regression
analyses identified that CVI can explain only 1% of the % age-predicted maximal HR
variability with a high standard error of estimate (~6.3%), indicating the absence
of a true physiological cause-effect relationship. In conclusion, the influence of
CVI on % of age-predicted maximal HR is null in healthy subjects, suggesting distinct
physiological mechanisms and potential clinical complementary role for these exercise-related
variables.
Key words
Parasympathetic - cardiopulmonary exercise testing - 4-s exercise test - healthy subjects
