title: Carotid baroreflex responsiveness in high-fit and sedentary young men.
abstract: The influence of fitness on cardiac vagal activity and baroreflex-mediated control of heart rate has not been clearly established in humans. Therefore, we studied resting cardiac vagal activity by evaluating respiratory sinus arrhythmia (RSA) and examined carotid-cardiac baroreflex responsiveness with a neck collar in 11 high-fit and 9 sedentary [based on maximal O2 consumption (VO2max) and history of physical activity] healthy young men (19-31 yr of age). Resting cardiac vagal activity was determined from the standard deviation of 100 consecutive resting R-R intervals. Baroreflex responsiveness was determined from the R-R interval responses to neck suction and pressure (repeated trials of 5-s stimuli of -20, -40, and 35 mmHg). Both RSA and the bradycardic (R-R interval) responses to neck suction of -40 mmHg were significantly greater (P less than 0.05) in the high-fit individuals (RSA, 116.5 +/- 11.5 ms; neck-suction response, 145.3 +/- 17.0 ms; mean +/- SE) compared with sedentary subjects (RSA, 65.2 +/- 6.6 ms; neck-suction response, 86.9 +/- 12.5 ms). Responses of the high-fit volunteers to the other intensities of neck stimuli (-20 and 35 mmHg) showed a similar trend but were not significantly different from those of the sedentary volunteers. The baroreflex slope derived from these data was significantly greater in the high-fit subjects (4.00 +/- 0.39 ms/mmHg) compared with the sedentary controls (2.53 +/- 0.28 ms/mmHg). These data suggest that resting cardiac vagal activity is greater, carotid-to-cardiac activity is well maintained, and baroreflex sensitivity, i.e., slope, is augmented in high-fit subjects.
authors.affiliation: Department of Physiology, Medical College of Wisconsin, Milwaukee.
authors.forename: J A
authors.initials: JA
authors.lastname: Barney
authors.forename: T J
authors.initials: TJ
authors.lastname: Ebert
authors.forename: L
authors.initials: L
authors.lastname: Groban
authors.forename: P A
authors.initials: PA
authors.lastname: Farrell
authors.forename: C V
authors.initials: CV
authors.lastname: Hughes
authors.forename: J J
authors.initials: JJ
authors.lastname: Smith
mesh_terms: D000328:Adult; D001146:Arrhythmia, Sinus / Q000503:physiopathology; D002346:Carotid Sinus / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D010809:Physical Fitness; D011311:Pressoreceptors / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology