Document Detail

Effects of gas density on experimentally obstructed ventilation during acute hypoxia.
MedLine Citation:
PMID:  10563443     Owner:  NLM     Status:  MEDLINE    
When patients with obstructive lung disease breathe helium-oxygen mixtures, their arterial PCO2, is lowered towards normal, indicating more effective ventilation. However, there is a lack of detailed respiratory data from clinical cases, so that the mechanisms remain unclear. To study relevant variables during hypoxemia and obstruction in the absence of disease, we undertook experiments with healthy subjects breathing normoxic and hypoxic gas mixtures of differing densities (air, 13.7% O2 in N2 and 13.7% O2 in helium) through an experimental obstruction (resistive airway loading). This increased airway resistance was twice that reported from the ambient-pleural pressure differences in patients with moderately severe emphysema. Without imposed resistance the total ventilation (VE) increased 27% on both hypoxic mixtures. With normoxia, the obstruction increased tidal volume but decreased frequency so that VE and alveolar ventilation (VA) were essentially unchanged. With hypoxia, breathing pattern changed similarly, but now VE decreased while VA was maintained. Helium returned the breathing patterns toward normal. Obstruction lowered the rapid increase in VE from two or three breaths of N2, but the decrease from two or three breaths of O2 was unchanged. We detected an increase in metabolic rate with obstructed breathing that was reduced by the helium mixtures. The remarkable finding was that despite the obstruction being markedly uncomfortable because of the high resistance, we did not find any substantial disturbance in gas exchange, compared to hypoxia with no obstruction. Thus, the main mechanisms responsible for improved blood gases in patients breathing helium mixtures were outside the scope of our experiment and likely related to disease factors.
J A Loeppky; D O Kuethe; S A Altobelli; P Scotto; J Piiper
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Respiration physiology     Volume:  117     ISSN:  0034-5687     ISO Abbreviation:  Respir Physiol     Publication Date:  1999 Sep 
Date Detail:
Created Date:  1999-11-30     Completed Date:  1999-11-30     Revised Date:  2009-11-11    
Medline Journal Info:
Nlm Unique ID:  0047142     Medline TA:  Respir Physiol     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  151-60     Citation Subset:  IM; S    
Lovelace Respiratory Research Institute, Albuquerque, NM 87108, USA.
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MeSH Terms
Airway Obstruction / physiopathology*
Airway Resistance
Anoxia / physiopathology*
Lung Diseases, Obstructive / physiopathology,  therapy
Oxygen Consumption
Pulmonary Alveoli / physiology
Pulmonary Ventilation*
Specific Gravity
Reg. No./Substance:
7440-59-7/Helium; 7727-37-9/Nitrogen; 7782-44-7/Oxygen

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

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