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

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

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Title		Cardiovascular determinants of maximal oxygen consumption in upright and supine posture at the end of prolonged bed rest in humans
Authors		Bringard, Aurélien Pogliaghi, Silvia Adami, Alessandra De Roia, Gabriela Lador, Frédéric Lucini, Daniela Pizzinelli, Paolo Capelli, Carlo Ferretti, Guido show all authors [1 - 9]
Published in		Respiratory Physiology & Neurobiology. 2010, vol. 172, no. 1-2, p. 53-62
Abstract		We tested the hypothesis that, after bed rest, maximal oxygen consumption ( VO₂max ) decreases more upright than supine, because of adequate cardiovascular response supine, but not upright. On 9 subjects, we determined VO₂max and maximal cardiac output (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 (f(H)) and stroke volume (Q(st)) were measured by a metabolic cart, electrocardiography and Modelflow from pulse pressure profiles, respectively. We computed Q as f(H) times Q(st), and systemic oxygen flow ( QaO₂) as 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, VO₂max was lower (p<0.05) than before, both upright (-38.6%) and supine (-17.0%), being 30.8% higher supine than upright. Maximal Q(st) decreased upright (-44.3%), but not supine (+3.7%), being 98.9% higher supine than upright. Maximal Q decreased upright (-45.1%), but not supine (+9.0%), being higher supine than upright (+98.4%). Maximal QaO₂ 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 VO₂max supine, (ii) partially explained the VO₂max decrease upright, and (iii) caused the VO₂max differences between postures. We speculate that impaired peripheral oxygen transfer and/or utilisation may explain the VO₂max decrease supine and the fraction of VO₂max decrease upright unexplained by cardiovascular responses.
Keywords		Bed Rest — Blood Pressure/physiology — Cardiac Output/physiology — Cardiovascular System — Heart Rate/physiology — Humans — Male — Oxygen Consumption/physiology — Posture/physiology — Respiratory Function Tests/methods — Stroke Volume/physiology — Supine Position/physiology — Young Adult
Identifiers		DOI: 10.1016/j.resp.2010.03.018 PMID: 20348037
Full text		Article (Published version) (530 Kb) - Limited access to UNIGE
Structures		Faculté de médecine / Section de médecine clinique / Département d'anesthésiologie, pharmacologie et soins intensifs Faculté de médecine / Section de médecine fondamentale / Département de neurosciences fondamentales
Citation (ISO format)		BRINGARD, Aurélien et al. Cardiovascular determinants of maximal oxygen consumption in upright and supine posture at the end of prolonged bed rest in humans. In: Respiratory Physiology & Neurobiology, 2010, vol. 172, n° 1-2, p. 53-62. https://archive-ouverte.unige.ch/unige:79559