Document Detail

Ventilatory responses to hypercapnia and hypoxia after 6 h passive hyperventilation in humans.
MedLine Citation:
PMID:  9882758     Owner:  NLM     Status:  MEDLINE    
1. Acute exposure to hypoxia stimulates ventilation and induces hypocapnia. Long-term exposure to hypoxia generates changes in respiratory control known as ventilatory acclimatization to hypoxia. The object of this study was to investigate the degree to which the hyperventilation and hypocapnia can induce the changes known as ventilatory acclimatization to hypoxia, in the absence of the primary hypoxic stimulus itself. 2. Three 6 h protocols were each performed on twelve healthy volunteers: (1) passive hypocapnic hyperventilation, with end-tidal CO2 pressure (PET,CO2) held 10 Torr below the eupnoeic value; (2) passive eucapnic hyperventilation, with PET,CO2 maintained eucapnic; (3) control. 3. Ventilatory responses to acute hypercapnia and hypoxia were assessed before and half an hour after each protocol. 4. The presence of prior hypocapnia, but not prior hyperventilation, caused a reduction in air-breathing PET,CO2 (P < 0.05, ANOVA), and a leftwards shift of the ventilatory response to hypercapnia (P < 0.05). The presence of prior hyperventilation, but not prior hypocapnia, caused an increase in the ventilatory sensitivity to CO2 (P < 0.05). No significant effects of any protocol were detected on the ventilatory sensitivity to hypoxia. 5. We conclude that following 6 h of passive hyperventilation: (i) the left shift of the VE-PET,CO2 relationship is due to alkalosis and not to hyperventilation; (ii) the increase in slope of the VE-PET,CO2 relationship is due to the hyperventilation and not the alkalosis; and (iii) ventilatory sensitivity to hypoxia is unaltered.
X Ren; P A Robbins
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of physiology     Volume:  514 ( Pt 3)     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  1999 Feb 
Date Detail:
Created Date:  1999-03-26     Completed Date:  1999-03-26     Revised Date:  2013-06-11    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  885-94     Citation Subset:  IM; S    
University Laboratory of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
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MeSH Terms
Acclimatization / physiology
Alkalosis / blood
Anoxia / physiopathology*
Carbon Dioxide / blood
Hypercapnia / physiopathology*
Hyperventilation / physiopathology*
Models, Biological
Respiratory Mechanics / physiology*
Ventilators, Mechanical
Grant Support
//Wellcome Trust
Reg. No./Substance:
124-38-9/Carbon Dioxide

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