Document Detail

Lower limb localized vascular phenomena explain initial orthostatic hypotension upon standing from squat.
MedLine Citation:
PMID:  21856921     Owner:  NLM     Status:  Publisher    
The cause(s) of initial orthostatic hypotension (transient fall in blood pressure within 15 s upon active rising) have not been established. We tested the hypothesis that this hypotension is due to local vascular phenomena in contracting leg muscles from the brief effort of standing up. Seventeen young healthy subjects (2 Male, 15 Female, 22.5 ±1.0 yrs) performed an active rise from resting squat after a 10 s squat, a 1 min squat, or a 5 min squat. Beat by beat arterial blood pressure, cardiac output, heart rate and stroke volume (Finometer finger photoplethysmography) and right common femoral artery blood flow (Doppler and Echo ultrasound) were recorded. Data are mean ±SEM. Quiet standing prior to squat represented baseline. Peak increases in lower limb and total vascular conductance (ml/min/mmHg) upon standing were not different within squat conditions (10 s squat 50.0 ±12.4 vs. 44.3 ±5.0, 1 min squat 54.7 ±9.2 vs. 50.5 ±4.5, 5 min squat 67.4 ±13.7 vs. 58.8 ±3.9 all P>0.574). Mean arterial blood pressure (mmHg) fell to a nadir well below standing baseline in all conditions despite increases in cardiac output. The hypotension predicted by the increase in leg vascular conductance accounted for this hypotension (observed vs. predicted (mmHg)); 10s squat -17.1 ±2.1 vs. -18.3 ±5.5, 1 min squat -22.0 ±3.8 vs. -25.3 ±4.9, 5 min squat -28.3 ±4.0 vs. -29.2 ±6.7). We conclude that rapid contraction induced dilation in leg muscles with the effort of standing, along with a minor potential contribution of elevated lower limb arterio-venous pressure gradient, outstrips compensatory CO responses and is the cause of initial orthostatic hypotension upon standing from squat.
Michael E Tschakovsky; Kristine Matusiak; Catherine Vipond; Lisa McVicar
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-8-19
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  -     ISSN:  1522-1539     ISO Abbreviation:  -     Publication Date:  2011 Aug 
Date Detail:
Created Date:  2011-8-22     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1Queen's University.
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