Document Detail

Hyperbaric bradycardia and hypoventilation in exercising men: effects of ambient pressure and breathing gas.
MedLine Citation:
PMID:  10517774     Owner:  NLM     Status:  MEDLINE    
We sought to determine whether hydrostatic pressure contributed to bradycardia and hypoventilation in hyperbaria. Eight men were studied during exercise at 50, 150, and 250 W while breathing 1) air at 1 bar, 2) helium-oxygen (He-O(2)) at 5.5 bar, 3) sulfur hexafluoride-oxygen (SF(6)-O(2)) at 1.3 bar, and 4) nitrogen-oxygen (N(2)-O(2)) at 5.5 bar. Gas densities were pairwise identical in 1) and 2), and 3) and 4), respectively. Increased hydrostatic pressure to 5.5 bar resulted in a modest but significant relative bradycardia on the order of 6 beats/min, in both the absence [1) vs. 2), P = 0. 0015] and presence [3) vs. 4), P = 0.029] of gases that are both denser than normal and mildly narcotic. In contrast, ventilatory responses appeared not to be influenced by hydrostatic pressure. Also, the combined exposure to increased gas density and mild-to-moderate inert gas narcosis at a given hydrostatic pressure [1) vs. 3), 2) vs. 4)] caused bradycardia (P = 0.032 and 0.061, respectively) of similar magnitude as 5.5-bar hydrostatic pressure. At the same time there was relative hypoventilation at the two higher workloads. We conclude that heart rate control, but not ventilatory control, is sensitive to relatively small increases in hydrostatic pressure.
D Linnarsson; A Ostlund; F Lind; C M Hesser
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  87     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  1999 Oct 
Date Detail:
Created Date:  1999-11-17     Completed Date:  1999-11-17     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:  1428-32     Citation Subset:  IM; S    
Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
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MeSH Terms
Atmospheric Pressure*
Bradycardia / etiology*
Drug Combinations
Exercise / physiology*
Heart Rate / physiology
Hydrostatic Pressure / adverse effects
Hypoventilation / etiology*
Sulfur Hexafluoride
Reg. No./Substance:
0/Drug Combinations; 0/Gases; 2551-62-4/Sulfur Hexafluoride; 7440-59-7/Helium; 7727-37-9/Nitrogen; 7782-44-7/Oxygen

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