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Research Article: Demetra D. Christou and Douglas R. Seals Decreased Maximal Heart Rate with Aging is Related to Reduced ß-adrenergic Responsiveness, but is Largely Explained by a Reduction in Intrinsic Heart Rate J Appl Physiol 2008; 0: 90401.2008v1 [Abstract] [PDF]

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Effect of aging on the contribution of vagal withdrawal to the chronotropic response to exercise

E.S. Prakash   (27 June 2008)

Effect of aging on the contribution of vagal withdrawal to the chronotropic response to exercise 27 June 2008
E.S. Prakash, Associate Professor School of Medicine, Asian Institute of Medicine, Science & Technology Send letter to journal: Re: Effect of aging on the contribution of vagal withdrawal to the chronotropic response to exercise dresprakash{at}gmail.com E.S. Prakash	Christou and Seals [1] have shown that 83% of the variance in age related decline in maximal heart rate (HR) during dynamic exercise is mainly due to a reduction in intrinsic HR and secondly due to a decrease in beta-adrenergic receptor responsiveness in the heart. The other physiologic mechanism which might account for the remaining variance is the extent to which cardiac vagal withdrawal contributes to increasing HR during exercise. The decrease in resting cardiac vagal tone with age would reduce chronotropic reserve by diminishing the extent to which cardiac vagal withdrawal can contribute to HR increments during exercise. Taylor, Hayano and Seals [2] have previously reported based on noninvasive estimates of RR variability that diminished cardiac vagal withdrawal contributes to the reduced HR increments during isometric handgrip exercise. In this study by Christou and Seals [1], the resting HR of young (mean 58 beats per minute, bpm) and old subjects (54 bpm) were very similar and the intrinsic HR in young and older subjects were respectively 83 and 58 bpm. The small difference between intrinsic and resting heart rate (of 4 bpm) clearly suggests that baseline cardiac vagal tone was minimal in the older subjects and it is probably reasonable to assume that the contribution of vagal withdrawal to HR increments during exercise was negligible. Conflict of interests: none References: [1] Christou D and Seals DR. Decreased maximal heart rate with aging is related to reduced ß-adrenergic responsiveness, but is largely explained by a reduction in intrinsic heart rate. Journal of Applied Physiology 2008, In Press doi:10.1152/japplphysiol.90401.2008 [2] Taylor, JA, Hayano J and Seals DR. Lesser vagal withdrawal during isometric exercise with age. Journal of Applied Physiology 79: 805-811, 1995.