Document Detail


Head down tilt at -6 degrees to -24 degrees can neutralize the cardiovascular effects of LBNP at -15 or -35 mmHg.
MedLine Citation:
PMID:  15558993     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
INTRODUCTION: The purpose of this study was to identify the combinations of head down tilt (HDT) and lower body negative pressure (LBNP) that would counterbalance each other's effects on cardiovascular and endocrine variables to produce a "neutral point" (NP). METHODS: We conducted 8 30-min experiments in 14 normotensive subjects (2 male, 12 female). Conditions included four levels of HDT (-6 degrees to -24 degrees) and two of LBNP (-15 and -35 mmHg). We determined blood plasma mass density, hematocrit, plasma aldosterone concentration, and plasma renin activity (PRA) before and at the end of stimulation. The effect of stimulus duration was tested using continuous measurements of heart rate (HR), blood pressure (BP), and thoracic electrical impedance (Z0). RESULTS: NPs were found for all variables except BP, which remained unchanged. NPs were similar for all variables. The 15 mmHg LBNP was compensated by 20 degrees HDT and 35 mmHg LBNP by 27.5 degrees HDT. Longer stimulus duration required increasing HDT angles to balance HR at 35 mmHg LBNP but had no influence on Z0 NP. DISCUSSION: Antiorthostatic positioning can compensate cardiovascular effects of LBNP in a similar fashion for all variables that are significantly influenced by LBNP and body angle, commensurate with stimulus magnitude. Arterial BP remained stable with stimulation and seems to be the primarily defended variable. Why stimulus duration seems to influence the NP for HR remains to be elucidated.
Authors:
Helmut Hinghofer-Szalkay; Bernd Haditsch; Ingrid Loder; Karl Pilz; Andreas Rössler; Daniela Jezova
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  75     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  2004 Nov 
Date Detail:
Created Date:  2004-11-22     Completed Date:  2005-04-28     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  United States    
Other Details:
Languages:  eng     Pagination:  947-51     Citation Subset:  IM; S    
Affiliation:
Institute for Adaptive and Spaceflight Physiology, Graz, Austria. helmut.hinghofer@meduni-graz.at
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MeSH Terms
Descriptor/Qualifier:
Adult
Aldosterone / blood
Cardiography, Impedance
Female
Heart Rate / physiology
Hematocrit
Hemodynamics / physiology*
Humans
Lower Body Negative Pressure*
Male
Plasma Volume / physiology
Posture / physiology*
Renin / blood
Chemical
Reg. No./Substance:
52-39-1/Aldosterone; EC 3.4.23.15/Renin

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


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