Cardiovascular re-adjustments and baroreflex response during clinical reambulation procedure at the end of 35-day bed rest in humans

Alessandra Adami, Paolo Pizzinelli, Aurélien Bringard, Carlo Capelli, Mara Malacarne, Daniela Lucini, Boštjan Simunič, Rado Pišot, Guido Ferretti

Research output: Contribution to journalArticlepeer-review

Abstract

During the reambulation procedure after 35-day head-down tilt bed rest (HDTBR) for 9 men, we recorded for the first time heart rate (HR; with electrocardiogram) and arterial pressure profiles (fingertip plethysmography) for 5 min in HDTBR and horizontal (SUP) positions, followed by 12 min in standing position, during which 4 subjects fainted (intolerant, INT) and were laid horizontal again (Recovery). We computed: mean arterial pressure (P̄; pressure profiles integral mean), stroke volume (SV; obtained with Modelflow method), and cardiac output (Q̇; SV × HR). All cardiovascular data remained stable in HDTBR and SUP for both groups (EXP). Taking the upright posture, EXP showed a decrease in SV and an increase in HR, becoming significantly different from SUP within 1 min. Further evolution of these parameters kept Q̇ stable in both groups until the second minute of standing. Afterward, in INT, P̄ precipitated without further HR increases: SV stopped being corrected and Q̈ reached 2.9 ± 0.4 L·min-1 at the last 15 s of standing. Sudden drop in P̄ allowed identification of a low-pressure threshold in INT (70.7 ± 12.9mm Hg), after which syncope occurred within 80 s. During Recovery, baroreflex curves showed a flat phase (P̄ increase, HR stable), followed by a steep phase (P̄ increased, HR decreased, starting when P̄ was 84.5 ± 12.5mm Hg and Q̇ was 9.6 ± 1.5 L·min-1). INT, in contrast with tolerant subjects, did not sustain standing because HR was unable to correct for the P̄ drop. These results indicate a major role for impaired arterial baroreflexes in the onset of orthostatic intolerance.

Original languageEnglish
Pages (from-to)673-680
Number of pages8
JournalApplied Physiology, Nutrition and Metabolism
Volume38
Issue number6
DOIs
Publication statusPublished - Jun 2013

Keywords

  • Baroreflex resetting
  • Bed rest of long duration
  • Orthostatic intolerance
  • Pressure threshold
  • Simulated microgravity
  • Weightlessness

ASJC Scopus subject areas

  • Physiology
  • Endocrinology, Diabetes and Metabolism
  • Nutrition and Dietetics
  • Physiology (medical)

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