Document Detail

Mechanisms of orthostatic intolerance following very prolonged exercise.
MedLine Citation:
PMID:  18483169     Owner:  NLM     Status:  MEDLINE    
Nine men completed a 24-h exercise trial, with physiological testing sessions before (T1, approximately 0630), during (T2, approximately 1640; T3, approximately 0045; T4, approximately 0630), and 48-h afterwards (T5, approximately 0650). Participants cycled and ran/trekked continuously between test sessions. A 24-h sedentary control trial was undertaken in crossover order. Within testing sessions, participants lay supine and then stood for 6 min, while heart rate variability (spectral analysis of ECG), middle cerebral artery perfusion velocity (MCAv), mean arterial pressure (MAP; Finometer), and end-tidal Pco(2) (Pet(CO(2))) were measured, and venous blood was sampled for cardiac troponin I. During the exercise trial: 1) two, six, and four participants were orthostatically intolerant at T2, T3, and T4, respectively; 2) changes in heart rate variability were only observed at T2; 3) supine MAP (baseline = 81 +/- 6 mmHg) was lower (P < 0.05) by 14% at T3 and 8% at T4, whereas standing MAP (75 +/- 7 mmHg) was lower by 16% at T2, 37% at T3, and 15% at T4; 4) Pet(CO(2)) was reduced (P < 0.05) at all times while supine (-3-4 Torr) and standing (-4-5 Torr) during exercise trial; 5) standing MCAv was reduced (P < 0.05) by 23% at T3 and 30% at T4 during the exercise trial; 6) changes in MCAv with standing always correlated (P < 0.01) with changes in Pet(CO(2)) (r = 0.78-0.93), but only with changes in MAP at T1, T2, and T3 (P < 0.05; r = 0.62-0.84); and 7) only two individuals showed minor elevations in cardiac troponin I. Recovery was complete within 48 h. During prolonged exercise, postural-induced hypotension and hypocapnia exacerbate cerebral hypoperfusion and facilitate syncope.
Samuel J E Lucas; James D Cotter; Carissa Murrell; Luke Wilson; J Greg Anson; David Gaze; Keith P George; Philip N Ainslie
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Publication Detail:
Type:  Journal Article     Date:  2008-05-15
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  105     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2008 Jul 
Date Detail:
Created Date:  2008-07-21     Completed Date:  2008-09-03     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  United States    
Other Details:
Languages:  eng     Pagination:  213-25     Citation Subset:  IM    
School of Physical Education, University of Otago, Dunedin, New Zealand.
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MeSH Terms
Blood Pressure / physiology
Carbon Dioxide / metabolism
Cerebrovascular Circulation / physiology
Data Interpretation, Statistical
Exercise / physiology*
Heart Diseases / metabolism,  physiopathology
Heart Rate / physiology
Hypotension, Orthostatic / physiopathology*
Posture / physiology
Pressoreceptors / physiology
Supine Position / physiology
Sympathetic Nervous System / physiology
Troponin I / metabolism
Vagus Nerve / physiology
Reg. No./Substance:
0/Troponin I; 124-38-9/Carbon Dioxide

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

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