title: Hypergravity exercise against bed rest induced changes in cardiac autonomic control.
abstract: An intermittent exposure to artificial hypergravity with physical exercise by a human centrifuge may provide a countermeasure against various physiological problems after space flight. To test the effects of hypergravity with ergometric exercise on dynamic regulation of heart rate during weightlessness, we quantified autonomic cardiovascular control before and after head-down-tilt bed rest (HDBR) with and without the countermeasure. Twelve male subjects underwent a 14-day period of HDBR. Six of them were exposed to a hypergravity (+1.2 Gz acceleration at heart level) for 30 min with ergometric exercise (60 W, n=4; 40 W, n=2) as a countermeasure on day 1, 2, 3, 5, 7, 9, 11, 12, 13 and 14, during HDBR (CM group). The remaining six were not exposed to a hypergravity exercise during HDBR (control group). Blood pressure and ECG were recorded at a supine position before and after HDBR. The high frequency power of R-R interval (HFRR; 1,008+/-238 to 353+/-56 ms(2) P<0.05) as an index of cardiac parasympathetic activity, and transfer function gain between BP and R-R interval in the high frequency range (GainHF; 21.9+/-5.4 to 14.5+/-4.2 ms/mmHg, P<0.01) as an index of vagally mediated arterial-cardiac baroreflex, decreased significantly after HDBR in the control group. However, these changes were not statistically significant in the CM group (HFRR, 1,150+/-344 to 768+/-385 ms(2); GainHF, 21.5+/-3.3 to 18.6+/-3.4 ms/mmHg). Moreover, baroreflex gain by sequence analysis showed similar results. This observation suggests that the intermittent exposure to hypergravity with ergometric exercise may attenuate the decreases in the parasympathetic activity and the spontaneous arterial-cardiac baroreflex function after weightlessness.
authors.affiliation: Department of Hygiene and Space Medicine, Nihon University School of Medicine, 30-1 Oyaguchi-Kamimachi, Itabasi-ku, Tokyo 173-8610, Japan. kiwasaki@med.nihon-u.ac.jp
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Iwasaki
authors.forename: Tomoki
authors.initials: T
authors.lastname: Shiozawa
authors.forename: Atsunori
authors.initials: A
authors.lastname: Kamiya
authors.forename: Daisaku
authors.initials: D
authors.lastname: Michikami
authors.forename: Kaname
authors.initials: K
authors.lastname: Hirayanagi
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Yajima
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iwase
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Mano
mesh_terms: D000328:Adult; D017704:Baroreflex; D001510:Bed Rest; D001794:Blood Pressure; D001810:Blood Volume; D015444:Exercise / Q000502:physiology*; D018475:Head-Down Tilt; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D006801:Humans; D018471:Hypergravity; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology*