Document Detail

Comparison of ventilatory responses to sustained reduction in arterial oxygen tension vs. content in awake ponies.
MedLine Citation:
PMID:  8063679     Owner:  NLM     Status:  MEDLINE    
To gain insight into central and peripheral contributions to changes in breathing during hypoxia, we compared effects on breathing of reducing inspired PO2 (hypoxic hypoxia) with reducing arterial O2 content (CaO2) through elevation of carboxy-hemoglobin (COHb) (CO hypoxia). Twelve awake ponies were studied during 1 h of breathing room air followed by 6 h when COHb was increased to 25% and CaO2 was decreased by 17%. When COHb was increased, arterial PCO2 (PaCO2) increased gradually to 1.3 Torr above (P < 0.05) control level between 30 and 45 min of CO exposure. Pulmonary ventilation (VE) decreased (P = 0.09) approximately 1 liter the first 30 min of CO exposure. After approximately 45 min, PaCO2 began to decrease, steadily reaching 1.5 Torr below (P < 0.05) control level by 4.5 h of CO hypoxia. VE did not change significantly after 30 min of elevated COHb. Eight ponies were also studied during 5 h of hypoxic hypoxia (arterial PO2 approximately 40 Torr). PaCO2 decreased 5 Torr (P < 0.05) within 5 min of hypoxia and decreased another 4 Torr (P < 0.05) between 30 min and 5 h of hypoxia consistent with hypoxic ventilatory acclimatization. VE increased (P < 0.05) within 3 min of hypoxic hypoxia but then decreased (P < 0.05; VE roll off) toward control and did not increase significantly with acclimatization. Because CO and hypoxic hypoxia both decrease brain oxygenation but only hypoxic hypoxia increases carotid chemoreceptor activity, we conclude that initial hypoventilation with CO hypoxia and VE roll off with hypoxic hypoxia are consistent with hypoxic ventilatory depression within the brain. In addition, hyperventilation with prolonged CO hypoxia is consistent with a central nervous system mechanism contributing to this phase of hypoxic ventilatory acclimatization in ponies.
T F Lowry; H V Forster; M J Korducki; A L Forster; M A Forster
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  76     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  1994 May 
Date Detail:
Created Date:  1994-09-22     Completed Date:  1994-09-22     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:  2147-53     Citation Subset:  IM    
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
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MeSH Terms
Anoxia / physiopathology
Blood Gas Analysis
Carbon Monoxide / pharmacology
Carboxyhemoglobin / metabolism
Carotid Body / physiology
Hypoxia, Brain / physiopathology
Oxygen / blood*
Respiration / physiology*
Respiratory Muscles / physiology
Grant Support
Reg. No./Substance:
630-08-0/Carbon Monoxide; 7782-44-7/Oxygen; 9061-29-4/Carboxyhemoglobin

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

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