| Project/Area Number |
12670070
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Environmental physiology (including Physical medicine and Nutritional physiology)
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| Research Institution | University of Occupational and Environmental Health |
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Principal Investigator |
SAGAWA Sueko University of Occupational and Environmental Health, Department of Physiology, School of Medicine Associate Professor, 医学部, 助教授 (20035489)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2001: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2000: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Keywords | microgravity / head-out immersion / head-down tilt / baroreflex sensitivity / neck chamber / cardiopulmonary baroreceptors / arterial baroreflex |
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| Research Abstract |
Cardiovascular deconditioning after space flight, including orthostatic intolerance, have been reported extensively, however, the mechanisms underlying the post flight orthostatic intolrerance are not well established. A marked cephalad fluid shift in microgravity may be one of the responsible factors for the reduction of baroreflex gain. In the present study, we examined whether a magnitude of the central hypervolemia induced by graded levels of immersion and head-down tilt (HDT) modifies the baroreflex control of heart rate (HR). The carotid baroreceptor-cardiac responsiveness was estimated by using a neck chamber technique in nine males. The experiments consisted of a 20-min resting in air (control), a 15-min water immersion each at the iliac crest, the xiphoid and the axilla, and a 30-min recovery in air. A level dependent decrease in intrathoracic impedance (P<0.05) and an increase in stroke volume (P<0.05) were detected to confirm an immersion level-dependent increase in the central blood volume. The maximum gain of the response curve at the level of the axilla was greater (P<0.05) than that of control, indicating increased baroreflex sensitivity. The baroreflex sensitivity of HR estimated by the sequence method was similarly high at immersion level of xiphoid and axilla (P<0.05) compared to that of control. There was no significant change in the sensitivity of baroreflex control of heart rate during HDT at 15?ー and 30?ー in 10 subjects. These results suggest that acute central hypervolemia increases the sensitivity of baroreflex control of HR. We suggest that cephalad blood shift per se unlikely plays a role in the reduction of baroreflex gain at microgravity.
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