Document Detail


A comparison of autonomic responses in humans induced by two simulation models of weightlessness: lower body positive pressure and 6 degrees head-down tilt.
MedLine Citation:
PMID:  10742547     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Six-degree head-down tilt (HDT) is well accepted as an effective weightlessness model in humans. However, some researchers utilized lower body positive pressure (LBPP) to simulate the cardiovascular and renal effects of a decreased gravitational stress. In order to determine whether LBPP was a suitable model for simulated weightlessness, we compared the differences between these two methods. Ten healthy males, aged 21-41 years, were subjected to graded LBPP at 10, 20 and 30 mmHg, as well as 6 degrees HDT. Muscle sympathetic nerve activity (MSNA) was microneurographically recorded from the tibial nerve along with cardiovascular variables. We found that MSNA decreased by 27% to a similar extent both at low levels of LBPP (10 and 20 mmHg) and HDT. However, at a high level of LBPP (30 mmHg), MSNA tended to increase. Mean arterial pressure was elevated significantly by 11% (10 mmHg) at 30 mmHg LBPP, but remained unchanged at low levels of LBPP and HDT. Heart rate did not change during the entire LBPP and HDT procedures. Total peripheral resistance markedly increased by 36% at 30 mmHg LBPP, but decreased by 9% at HDT. Both stroke volume and cardiac output tended to decrease at 30 mmHg LBPP, but increased at HDT. These results suggest that although both LBPP and HDT induce fluid shifts from the lower body toward the thoracic compartment, autonomic responses are different, especially at LBPP greater than 20 mmHg. We note that high levels of LBPP (>20 mmHg) activate not only cardiopulmonary and arterial baroreflexes, but also intramuscular mechanoreflexes, while 6 degrees HDT only activates cardiopulmonary baroreflexes. We conclude that LBPP is not a suitable model for simulated weightlessness in humans.
Authors:
Q Fu; Y Sugiyama; A Kamiya; T Mano
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Publication Detail:
Type:  Comparative Study; Journal Article    
Journal Detail:
Title:  Journal of the autonomic nervous system     Volume:  80     ISSN:  0165-1838     ISO Abbreviation:  J. Auton. Nerv. Syst.     Publication Date:  2000 Apr 
Date Detail:
Created Date:  2000-05-31     Completed Date:  2000-05-31     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8003419     Medline TA:  J Auton Nerv Syst     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  101-7     Citation Subset:  IM; S    
Affiliation:
Department of Autonomic Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan.
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MeSH Terms
Descriptor/Qualifier:
Adult
Blood Pressure / physiology*
Electrocardiography
Heart Rate / physiology
Humans
Leg
Male
Posture / physiology
Pressoreceptors / physiology*
Pressure
Stroke Volume / physiology
Sympathetic Nervous System / physiology*
Tilt-Table Test
Weightlessness Simulation*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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