Document Detail

Effects of inspired O2 and CO2 on ventilatory responses to LBNP-release and acute head-down tilt.
MedLine Citation:
PMID:  7487808     Owner:  NLM     Status:  MEDLINE    
Increases in blood flow and CO2 return to the heart and lungs at the onset of exercise have been proposed to initiate reflexive feedback which increases ventilation (VE), via mechanoreceptors in the heart and/or intrapulmonary CO2 flow receptors. Both lower body negative pressure (-40 mm Hg) release (LBNP-release) and acute head-down (-30 degrees) tilt (TILT) provide physiological models to focus upon the effects of increased venous return and CO2 flow on VE, without the confounding influence of limb afferents or the descending efferents associated with central command. We examined the ventilatory responses to LBNP-release and TILT while inhaling one of four gas mixtures: a) room air (R); b) 95% O2 (O); c) 95% O2, 1.25% CO2 (LC); and d) 95% O2, 2.25% CO2 (HC). Breath-by-breath measurements for VE end-tidal CO2 (PETCO2), tidal volume (VT), and breathing frequency (fB) were taken. VE and VT for HC were significantly higher (p < 0.05) than those for R, O, and LC throughout the test session, while fB and PETCO2 were not significantly different among the gas treatments. VE increased (p < 0.05) above resting baseline with LBNP-release and TILT for R, O, LC, and HC primarily through an elevation of fB. Further, the maximal change in VE following LBNP-release or TILT were not different among inhaled gas mixtures. However, area under the VE curve following LBNP-release and TILT was higher for HC compared to the other gas mixtures. We conclude that these results are inconsistent with the theory that carotid bodies are essential in driving VE with these models.(ABSTRACT TRUNCATED AT 250 WORDS)
J M Lawler; C C Cline; J A O'Kroy; J R Coast
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  66     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  1995 Aug 
Date Detail:
Created Date:  1995-12-04     Completed Date:  1995-12-04     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  751-6     Citation Subset:  IM; S    
Eloise Beard Smith Human Performance Laboratories, Dept. of Health & Kinesiology, Texas A&M University, College Station 77843-4243, USA.
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MeSH Terms
Carbon Dioxide / administration & dosage,  metabolism*
Head-Down Tilt / physiology*
Lower Body Negative Pressure*
Oxygen / administration & dosage,  metabolism*
Respiration / physiology*
Respiratory Mechanics / physiology
Reg. No./Substance:
124-38-9/Carbon Dioxide; 7782-44-7/Oxygen

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