• Home
  1. Home
  2. Phase I dynamics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men in acute normobaric hypoxia
Scientific article
English

Phase I dynamics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men in acute normobaric hypoxia

Contributors

Lador, Frédéric; Tam, Enrico; Azabji Kenfack, Marcel; Cautero, Michela; Moia, Christian; Morel, Denis; Capelli, Carlo; Ferretti, Guido

Published in

American journal of physiology. Regulatory, integrative and comparative physiology, vol. 295, no. 2, p. R624-632

Publication date

2008

Abstract

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.

Keywords

  • Adult
  • Anoxia/metabolism/physiopathology
  • Baroreflex
  • Blood Pressure
  • Carbon Dioxide/blood
  • Cardiac Output
  • Electrocardiography
  • Exercise
  • Heart/innervation
  • Heart Rate
  • Hemoglobins/metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Kinetics
  • Lung/metabolism
  • Male
  • Models, Cardiovascular
  • Myocardial Contraction
  • Oxygen/blood
  • Oxygen Consumption
  • Stroke Volume
  • Vagus Nerve/physiopathology
  • Vascular Resistance

UNIGE affiliation entities

UNIGE research groups

Citation (ISO format)

LADOR, Frédéric et al. Phase I dynamics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men in acute normobaric hypoxia. In: American journal of physiology. Regulatory, integrative and comparative physiology, 2008, vol. 295, n° 2, p. R624–632. doi: 10.1152/ajpregu.00797.2007

Main files (1)

Article (Accepted version)

Identifiers

Additional URL for this publication

http://ajpregu.physiology.org/cgi/content/full/295/2/R624

Journal ISSN

0363-6119
665views
0downloads

Technical informations

Creation

11/06/2009 10:22:00

First validation

11/06/2009 10:22:00

Update

14/03/2023 15:06:35

Status update

14/03/2023 15:06:35

Last indexation

29/10/2024 11:42:25
All rights reserved by Archive ouverte UNIGE and the University of Geneva
OpenAIRE Indexed & Validated