Cardiovascular determinants of maximal oxygen consumption in upright and supine posture at the end of prolonged bed rest in humans

Aurélien Bringard, Silvia Pogliaghi, Alessandra Adami, Gabriela De Roia, Frédéric Lador, Daniela Lucini, Paolo Pizzinelli, Carlo Capelli, Guido Ferretti

Research output: Contribution to journalArticle

Abstract

We tested the hypothesis that, after bed rest, maximal oxygen consumption (over(V, ̇)O2 max) decreases more upright than supine, because of adequate cardiovascular response supine, but not upright. On 9 subjects, we determined over(V, ̇)O2 max and maximal cardiac output (over(Q, ̇)) upright and supine, before and after (reambulation day upright, the following day supine) 35-day bed rest, by classical steady state protocol. Oxygen consumption, heart rate (fH) and stroke volume (Qst) were measured by a metabolic cart, electrocardiography and Modelflow from pulse pressure profiles, respectively. We computed over(Q, ̇) as fH times Qst, and systemic oxygen flow (over(Q, ̇) aO2) as over(Q, .) times arterial oxygen concentration, obtained after haemoglobin and arterial oxygen saturation measurements. Before bed rest, all parameters at maximal exercise were similar upright and supine. After bed rest, over(V, ̇)O2 max was lower (p <0.05) than before, both upright (-38.6%) and supine (-17.0%), being 30.8% higher supine than upright. Maximal Qst decreased upright (-44.3%), but not supine (+3.7%), being 98.9% higher supine than upright. Maximal over(Q, ̇) decreased upright (-45.1%), but not supine (+9.0%), being higher supine than upright (+98.4%). Maximal over(Q, ̇) aO2 decreased upright (-37.8%), but not supine (+14.8%), being higher (+74.8%) upright than supine. After bed rest, the cardiovascular response (i) did not affect over(V, ̇)O2 max supine, (ii) partially explained the over(V, ̇)O2 max decrease upright, and (iii) caused the over(V, ̇)O2 max differences between postures. We speculate that impaired peripheral oxygen transfer and/or utilisation may explain the over(V, ̇)O2 max decrease supine and the fraction of over(V, ̇)O2 max decrease upright unexplained by cardiovascular responses.

Original languageEnglish
Pages (from-to)53-62
Number of pages10
JournalRespiratory Physiology and Neurobiology
Volume172
Issue number1-2
DOIs
Publication statusPublished - Jun 30 2010

Keywords

  • Cardiac output
  • Cardiovascular response
  • Exercise capacity
  • Simulated microgravity

ASJC Scopus subject areas

  • Physiology
  • Pulmonary and Respiratory Medicine
  • Neuroscience(all)

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