title: Enhancement of parasympathetic cardiac activity during activation of muscle metaboreflex in humans.
abstract: We measured the changes in heart rate (HR) variability estimated from the standard deviation of the R-R intervals to evaluate cardiac parasympathetic tone noninvasively before and during activation of muscle metaboreflex induced by postexercise muscle ischemia. Eight healthy male subjects performed sustained handgrip at 50% maximal voluntary contraction followed by forearm occlusion. Mean arterial pressure, cardiac stroke volume, and ratio of cardiac preejection period to left ventricular ejection time (PEP/LVET) were also measured. During the 2-min occlusion after 60 s of handgrip with voluntary respiration, HR variability and mean arterial pressure were significantly increased from baseline (54.4 +/- 6.1 to 80.1 +/- 12.8 ms and 81 +/- 1 to 99 +/- 3 mmHg, respectively) and PEP/LVET was decreased from resting level of 0.404 +/- 0.022 to 0.363 +/- 0.036. During occlusion and recovery, HR did not change from baseline level in any experiment. There was no influence of occlusion itself or of cessation of exercise per se on any parameters. Although overall enhanced HR variability was seen, probably due to lower breathing frequency and larger tidal volume, similar results were also obtained from an experiment with controlled respiration, showing that the increase in HR variability was not due to the changes in tidal volume or breathing frequency during occlusion. In conclusion, the HR variability is increased during activation of the muscle metaboreflex induced by postexercise muscle ischemia in humans. This finding shows that the parasympathetic cardiac tone is enhanced during activation of the muscle metaboreflex in humans and balances enhanced cardiac sympathetic activity to result in an unchanged HR.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biomechanics and Physiology, Faculty of Liberal arts, Yamaguchi University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Nishiyasu
authors.forename: N
authors.initials: N
authors.lastname: Tan
authors.forename: K
authors.initials: K
authors.lastname: Morimoto
authors.forename: M
authors.initials: M
authors.lastname: Nishiyasu
authors.forename: Y
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: N
authors.initials: N
authors.lastname: Murakami
mesh_terms: D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism*; D010275:Parasympathetic Nervous System / Q000502:physiology*; D005082:Physical Exertion; D012018:Reflex; D012039:Regional Blood Flow; D013318:Stroke Volume