title: Exercise training augments the dynamic heart rate response to vagal but not sympathetic stimulation in rats.
abstract: We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained (16 wk, treadmill for 1 h, 5 times/wk at 15 m/min and 15-degree grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats·min(-1)·Hz(-1); natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s; sedentary vs. exercise trained, respectively, means ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats·min(-1)·Hz(-1) in the exercise-trained group (P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very-low-frequency and low-frequency bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for very-low-frequency, low-frequency, and high-frequency bands, exercise training produced a significant group effect (P < 0.05 by two-way, repeated-measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation, regardless of the frequency bands.
authors.affiliation: Dept. of Physical Therapy, Univ. of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75390-9174, USA. masaki.mizuno@utsouthwestern.edu
authors.forename: Masaki
authors.initials: M
authors.lastname: Mizuno
authors.forename: Toru
authors.initials: T
authors.lastname: Kawada
authors.forename: Atsunori
authors.initials: A
authors.lastname: Kamiya
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Miyamoto
authors.forename: Shuji
authors.initials: S
authors.lastname: Shimizu
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Shishido
authors.forename: Scott A
authors.initials: SA
authors.lastname: Smith
authors.forename: Masaru
authors.initials: M
authors.lastname: Sugimachi
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D006339:Heart Rate / Q000502:physiology*; D008297:Male; D023421:Models, Animal; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*