Effect of dynamic exercise on human carotid-cardiac baroreflex latency.
We compared the beat-to-beat responses of heart rate (HR) after brief activation of carotid baroreceptors in resting humans with the responses obtained during mild-to-moderate levels of dynamic exercise [25 and 50% of peak O2 uptake (VO2peak)] to investigate the effect of exercise on baroreflex latency. Carotid baroreceptors were activated by a pressure pulse (5 s) of neck suction (NS, -80 Torr) and neck pressure (NP, +40 Torr) during held expiration. At rest the peak change in HR to NS/NP occurred during the first several heartbeats (1st-3rd beat), whereas during mild and moderate exercise peak HR responses occurred near the end of the NS/NP pulse (6th-8th beat). In contrast, time (s) to the peak change in HR was not different between rest and exercise (P > 0.05). Reflex tachycadia to NP progressively decreased during exercise (17 +/- 3, 10 +/- 1, and 4 +/- 1% of control, rest vs. 25% VO2peak, vs. 50% VO2peak, respectively, P < 0.05), and a strong positive correlation was found between the magnitude of the reflex tachycardia and a measure of HR variability (cardiac vagal tone index, r = 0.74, P < 0.0001). Reflex bradycardia to NS gradually increased during exercise (13 +/- 2, 17 +/- 2, and 18 +/- 2% of control, rest vs. 25% VO2peak, vs. 50% VO2peak, respectively, P = 0.10) and was negatively correlated with cardiac vagal tone (r = 0.42, P < 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)
Potts
J T
JT
Department of Physiology, University of North Texas Health Science Center, Fort Worth 76107.
Raven
P B
PB
D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001919:Bradycardia / Q000503:physiopathology; D002320:Cardiovascular Physiological Phenomena; D002346:Carotid Sinus / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009333:Neck; D010101:Oxygen Consumption / Q000502:physiology; D011312:Pressure; D013396:Suction; D013610:Tachycardia / Q000503:physiopathology; D014630:Vagus Nerve / Q000502:physiology