Document Detail

Phase I dynamics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men in acute normobaric hypoxia.
MedLine Citation:
PMID:  18495828     Owner:  NLM     Status:  MEDLINE    
We tested the hypothesis that vagal withdrawal plays a role in the rapid (phase I) cardiopulmonary response to exercise. To this aim, in five men (24.6+/-3.4 yr, 82.1+/-13.7 kg, maximal aerobic power 330+/-67 W), we determined beat-by-beat cardiac output (Q), oxygen delivery (QaO2), and breath-by-breath lung oxygen uptake (VO2) at light exercise (50 and 100 W) in normoxia and acute hypoxia (fraction of inspired O2=0.11), because the latter reduces resting vagal activity. We computed Q from stroke volume (Qst, by model flow) and heart rate (fH, electrocardiography), and QaO2 from Q and arterial O2 concentration. Double exponentials were fitted to the data. In hypoxia compared with normoxia, steady-state fH and Q were higher, and Qst and VO2 were unchanged. QaO2 was unchanged at rest and lower at exercise. During transients, amplitude of phase I (A1) for VO2 was unchanged. For fH, Q and QaO2, A1 was lower. Phase I time constant (tau1) for QaO2 and VO2 was unchanged. The same was the case for Q at 100 W and for fH at 50 W. Qst kinetics were unaffected. In conclusion, the results do not fully support the hypothesis that vagal withdrawal determines phase I, because it was not completely suppressed. Although we can attribute the decrease in A1 of fH to a diminished degree of vagal withdrawal in hypoxia, this is not so for Qst. Thus the dual origin of the phase I of Q and QaO2, neural (vagal) and mechanical (venous return increase by muscle pump action), would rather be confirmed.
Frédéric Lador; Enrico Tam; Marcel Azabji Kenfack; Michela Cautero; Christian Moia; Denis R Morel; Carlo Capelli; Guido Ferretti
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2008-05-21
Journal Detail:
Title:  American journal of physiology. Regulatory, integrative and comparative physiology     Volume:  295     ISSN:  0363-6119     ISO Abbreviation:  Am. J. Physiol. Regul. Integr. Comp. Physiol.     Publication Date:  2008 Aug 
Date Detail:
Created Date:  2008-08-11     Completed Date:  2008-09-09     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901230     Medline TA:  Am J Physiol Regul Integr Comp Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  R624-32     Citation Subset:  IM    
Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1 rue Michel Servet, CH-1211 Genève 4, Switzerland.
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MeSH Terms
Anoxia / metabolism,  physiopathology*
Blood Pressure
Carbon Dioxide / blood
Cardiac Output*
Heart / innervation*
Heart Rate
Hemoglobins / metabolism
Hydrogen-Ion Concentration
Lung / metabolism*
Models, Cardiovascular
Myocardial Contraction
Oxygen / blood*
Oxygen Consumption*
Stroke Volume
Vagus Nerve / physiopathology*
Vascular Resistance
Reg. No./Substance:
0/Hemoglobins; 124-38-9/Carbon Dioxide; 7782-44-7/Oxygen

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

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