Prolonged head down bed rest-induced inactivity impairs tonic autonomic regulation while sparing oscillatory cardiovascular rhythms in healthy humans

Guido Ferretti, Ferdinando Iellamo, Paolo Pizzinelli, Marcel A. Kenfack, Frédéric Lador, Daniela Lucini, Alberto Porta, Krzysztof Narkiewicz, Massimo Pagani

Research output: Contribution to journalArticle

Abstract

BACKGROUND: Physical inactivity represents a major risk for cardiovascular disorders, such as hypertension, myocardial infarction or sudden death; however, underlying mechanisms are not clearly elucidated. Clinical and epidemiological investigations suggest, beyond molecular changes, the possibility of an induced impairment in autonomic cardiovascular regulation. However, this hypothesis has not been tested directly. METHODS: Accordingly, we planned a study with noninvasive, minimally intrusive, techniques on healthy volunteers. Participants were maintained for 90 days strictly in bed, 24 h a day, in head-down (-6°) position (HDBR). Physical activity was thus virtually abolished for the entire period of HDBR. We examined efferent muscle sympathetic nerve activity, as a measure of vascular sympathetic control, baroreceptor reflex sensitivity, heart rate variability (assessing cardiovagal regulation), RR and systolic arterial pressure and low-frequency and high-frequency normalized components (as a window on central oscillatory regulation). Measures were obtained at rest and during simple maneuvers (moderate handgrip, lower body negative pressure and active standing) to assess potential changes in autonomic cardiovascular responsiveness to standard stimuli and the related oscillatory profiles. RESULTS: HDBR transiently reduced muscle sympathetic nerve activity, RR, heart rate variability and baroreceptor reflex sensitivity late during HDBR or early during the recovery phase. Conversely, oscillatory profiles of RR and systolic arterial pressure variability were maintained throughout. Responsiveness to test stimuli was also largely maintained. CONCLUSION: Prolonged inactivity as induced by HDBR in healthy volunteers reduces both cardiovagal and vascular sympathetic regulation, while largely maintaining peripheral responsiveness to standardized stimuli and sparing the functional structure of central oscillatory cardiovascular regulation.

Original languageEnglish
Pages (from-to)551-561
Number of pages11
JournalJournal of Hypertension
Volume27
Issue number3
DOIs
Publication statusPublished - Mar 2009

Keywords

  • Autonomic nervous system
  • Baroreflex
  • Cardiovascular oscillations
  • Cardiovascular regulation
  • Inactivity
  • Sympathetic regulation
  • Vagal regulation

ASJC Scopus subject areas

  • Internal Medicine
  • Physiology
  • Cardiology and Cardiovascular Medicine

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