Document Detail

Plasma volume restoration with salt tablets and water after bed rest prevents orthostatic hypotension and changes in supine hemodynamic and endocrine variables.
MedLine Citation:
PMID:  15486040     Owner:  NLM     Status:  MEDLINE    
Head-down bed rest changes the values of many cardiovascular and endocrine variables and also elicits significant hypovolemia. Because previous studies had not controlled for hypovolemia, it is unknown whether the reported changes were primary effects of bed rest or secondary effects of bed rest-induced hypovolemia. We hypothesized that restoring plasma volume with salt tablets and water after 12 days of head-down bed rest would result in an absence of hemodynamic and endocrine changes and a reduced incidence of orthostatic hypotension. In 10 men, we measured changes from pre-bed-rest to post-bed-rest in venous and arterial pressures; heart rate; stroke volume; cardiac output; vascular resistance; plasma norepinephrine, epinephrine, vasopressin, renin activity (PRA), and aldosterone responses to different tilt levels (0 degrees, -10 degrees, 20 degrees, 30 degrees, and 70 degrees); and plasma volume and platelet alpha2- and lymphocyte beta2-adrenoreceptor densities and affinities (0 degrees tilt only). Fluid loading at the end of bed rest restored plasma volume and resulted in the absence of post-bed-rest orthostatic hypotension and changes in supine hemodynamic and endocrine variables. Fluid loading did not prevent post-bed-rest increases in beta2-adrenoreceptor density or decreases in the aldosterone-to-PRA ratio (P = 0.05 for each). Heart rate, epinephrine, and PRA responses to upright tilt after bed rest were increased (P < 0.05), despite the fluid load. These results suggest that incidents of orthostatic hypotension and many of the changes in supine hemodynamic and endocrine variables in volume-depleted bed-rested subjects occur secondarily to the hypovolemia. Despite normovolemia after bed rest, beta2-adrenoreceptors were upregulated, and heart rate, epinephrine, and PRA responses to tilt were augmented, indicating that these changes are independent of volume depletion.
Wendy W Waters; Steven H Platts; Brett M Mitchell; Peggy A Whitson; Janice V Meck
Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2004-10-14
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  288     ISSN:  0363-6135     ISO Abbreviation:  Am. J. Physiol. Heart Circ. Physiol.     Publication Date:  2005 Feb 
Date Detail:
Created Date:  2005-01-14     Completed Date:  2005-02-23     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  H839-47     Citation Subset:  IM; S    
Human Adaptation and Countermeasures Office, Wyle Laboratories, Inc., Houston, Texas, USA.
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MeSH Terms
Aldosterone / blood
Baroreflex / physiology
Bed Rest / adverse effects*
Blood Pressure / physiology
Endocrine System / physiology
Epinephrine / blood
Heart Rate / physiology
Hypotension, Orthostatic / etiology,  physiopathology*,  prevention & control*
Norepinephrine / blood
Plasma Volume / physiology*
Receptors, Adrenergic / physiology
Renin / blood
Sodium Chloride / administration & dosage*
Space Flight
Stroke Volume / physiology
Supine Position
Vascular Resistance / physiology
Vasopressins / blood
Weightlessness Simulation / adverse effects
Reg. No./Substance:
0/Receptors, Adrenergic; 11000-17-2/Vasopressins; 51-41-2/Norepinephrine; 51-43-4/Epinephrine; 52-39-1/Aldosterone; 7647-14-5/Sodium Chloride; EC

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

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