Orthostatic intolerance: emerging genetic and environmental etiologies.
J Gravit Physiol
; 6(1): P51-4, 1999 Jul.
Article
in En
| MEDLINE
| ID: mdl-11543025
ABSTRACT
Orthostatic intolerance (OI) is common after space flight and resembles the disabling idiopathic orthostatic intolerance commonly observed in otherwise healthy young individuals. OI can arise from reduced sympathetic nervous system activity and, paradoxically, also from increased sympathetic nervous system activity. Patients with early manifestations of pure autonomic failure demonstrate an etiology based upon reduced sympathetic nervous system activity. Patients with hyperadrenergia demonstrate an etiology based on increased sympathetic nervous activity. For many years, we have recognized that the microgravity environment induces adaptation in the cardiovascular system and its autonomic control mechanisms that lead to the presence of OI on return to gravity. Understanding the nature of OI in astronauts returning from space as well as in the relevant patient population on earth has been a priority of Vanderbilt's Center for Space Physiology and Medicine in recent years. A major purpose of the autonomic experiment in the Neurolab mission was to identify whether the OI experienced by astronauts on return to earth was best explained by a hypoadrenergic or hyperadrenergic state. To address this question, we analyzed sympathetic nervous system activity inflight by 1) measurement of plasma catecholamines; 2) assessment of peroneal microneurographic sympathetic nerve traffic; and 3) assessment of norepinephrine spillover and clearance during infusion of tritiated norepinephrine. These studies documented a slight (five bursts per minute) increase in muscle sympathetic nerve activity, a 200 pg/ml increase in plasma norepinephrine level, and a 350 ng/min increase in norepinephrine clearance. Plasma norepinephrine and norepinephrine spillover and clearance were also raised on recovery day. These data indicate that enhanced sympathetic activation, rather than reduced sympathetic activation, accompanies the orthostatic intolerance following microgravity.
Key words
Search on Google
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Space Flight
/
Autonomic Nervous System Diseases
/
Weightlessness
/
Hypotension, Orthostatic
Type of study:
Etiology_studies
Limits:
Humans
Language:
En
Journal:
J Gravit Physiol
Journal subject:
FISIOLOGIA
Year:
1999
Document type:
Article
Affiliation country:
United States