Document Detail

Chemoreceptor responsiveness in fetal sheep.
MedLine Citation:
PMID:  1636755     Owner:  NLM     Status:  MEDLINE    
Fetal peripheral chemoreceptor responses to arterial O2 saturation and changes in PCO2 have not yet been quantitated. In 24 late-term chronically instrumented fetal sheep, we measured the heart rate response to acute hypoxemia induced by uterine arterial occlusion at various resting O2 saturations (25-86%) and at induced reductions and increases in baseline O2 saturation. As an index of fetal chemoreceptor responsiveness we calculated the fall in heart rate divided by the fall in arterial O2 saturation (delta HR/delta sat). delta HR/delta sat was inversely related to resting O2 saturation at levels less than 65%, but greater than 65% this relationship was no longer present. However, an induced increase in baseline O2 saturation from 66 +/- 12 to 76 +/- 10% decreased delta HR/delta sat from 2.6 +/- 1.6 to 1.8 +/- 1.0, indicating that when resting O2 saturation is greater than 65% there may be adaptation of peripheral chemoreceptors. Below 65%, an induced decrease in baseline O2 saturation increased delta HR/delta sat (to 3.8 +/- 1.8), suggesting a lack of adaptation to lower O2 saturations. Concomitant changes in PCO2, or differences in baseline PCO2, did not affect delta HR/delta sat during uterine arterial occlusion, which suggests that there is no interdependence between O2 and CO2 as a stimulus for the fetal peripheral chemoreceptor. However, acute hypercapnia (n = 24 in 8 fetal sheep) induced bradycardia. Furthermore, this bradycardia was related to the increase in fetal arterial PCO2. We conclude that the fetal peripheral chemoreceptor is sensitive to hypoxemia and hypercapnia and that the hypoxemia response is accentuated with decreases in initial O2 saturation.
P F Boekkooi; J Baan; D Teitel; A M Rudolph
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The American journal of physiology     Volume:  263     ISSN:  0002-9513     ISO Abbreviation:  Am. J. Physiol.     Publication Date:  1992 Jul 
Date Detail:
Created Date:  1992-08-24     Completed Date:  1992-08-24     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370511     Medline TA:  Am J Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  H162-7     Citation Subset:  IM    
Cardiovascular Research Institute, University of California, San Francisco 94143.
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MeSH Terms
Acute Disease
Anoxia / blood,  physiopathology*
Carbon Dioxide / blood
Chemoreceptor Cells / physiology*
Fetus / physiology*
Heart Rate
Hypercapnia / blood,  physiopathology
Oxygen / blood
Grant Support
Reg. No./Substance:
124-38-9/Carbon Dioxide; 7782-44-7/Oxygen

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