Document Detail

Role of the autonomic nervous system in the reduced maximal cardiac output at altitude.
MedLine Citation:
PMID:  12070214     Owner:  NLM     Status:  MEDLINE    
After acclimatization to high altitude, maximal exercise cardiac output (QT) is reduced. Possible contributing factors include 1) blood volume depletion, 2) increased blood viscosity, 3) myocardial hypoxia, 4) altered autonomic nervous system (ANS) function affecting maximal heart rate (HR), and 5) reduced flow demand from reduced muscle work capability. We tested the role of the ANS reduction of HR in this phenomenon in five normal subjects by separately blocking the sympathetic and parasympathetic arms of the ANS during maximal exercise after 2-wk acclimatization at 3,800 m to alter maximal HR. We used intravenous doses of 8.0 mg of propranolol and 0.8 mg of glycopyrrolate, respectively. At altitude, peak HR was 170 +/- 6 beats/min, reduced from 186 +/- 3 beats/min (P = 0.012) at sea level. Propranolol further reduced peak HR to 139 +/- 2 beats/min (P = 0.001), whereas glycopyrrolate increased peak HR to sea level values, 184 +/- 3 beats/min, confirming adequate dosing with each drug. In contrast, peak O(2) consumption, work rate, and QT were similar at altitude under all drug treatments [peak QT = 16.2 +/- 1.2 (control), 15.5 +/- 1.3 (propranolol), and 16.2 +/- 1.1 l/min (glycopyrrolate)]. All QT results at altitude were lower than those at sea level (20.0 +/- 1.8 l/min in air). Therefore, this study suggests that, whereas the ANS may affect HR at altitude, peak QT is unaffected by ANS blockade. We conclude that the effect of altered ANS function on HR is not the cause of the reduced maximal QT at altitude.
Harm J Bogaard; Susan R Hopkins; Yoshiki Yamaya; Kyuichi Niizeki; Michael G Ziegler; Peter D Wagner
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  93     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2002 Jul 
Date Detail:
Created Date:  2002-06-18     Completed Date:  2002-12-17     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:  271-9     Citation Subset:  IM    
Division of Physiology, Department of Medicine, University of California, San Diego, La Jolla 92093, USA.
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MeSH Terms
Acclimatization / physiology
Acetylene / diagnostic use
Adrenergic beta-Antagonists / pharmacology
Autonomic Nervous System / physiology*
Cardiac Output / physiology*
Glycopyrrolate / pharmacology
Heart Rate / physiology
Muscarinic Antagonists / pharmacology
Oxygen Consumption / physiology
Propranolol / pharmacology
Stroke Volume / physiology
Grant Support
Reg. No./Substance:
0/Adrenergic beta-Antagonists; 0/Muscarinic Antagonists; 525-66-6/Propranolol; 596-51-0/Glycopyrrolate; 74-86-2/Acetylene

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