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.
Cardiovascular re-adjustments and baroreflex response during clinical reambulation procedure at the end of 35-day bed rest in humans / A. Adami, P. Pizzinelli, A. Bringard, C. Capelli, M. Malacarne, D. Lucini, B. Simunič, R. Pišot, G. Ferretti. - In: APPLIED PHYSIOLOGY, NUTRITION AND METABOLISM. - ISSN 1715-5312. - 38:6(2013), pp. 673-680.
|Titolo:||Cardiovascular re-adjustments and baroreflex response during clinical reambulation procedure at the end of 35-day bed rest in humans|
|Parole Chiave:||Baroreflex resetting; Bed rest of long duration; Orthostatic intolerance; Pressure threshold; Simulated microgravity; Weightlessness; Cardiac Output; Cardiovascular System; Heart Rate; Humans; Baroreflex; Bed Rest; Physiology; Endocrinology, Diabetes and Metabolism; Nutrition and Dietetics; Physiology (medical); Medicine (all)|
|Settore Scientifico Disciplinare:||Settore M-EDF/01 - Metodi e Didattiche delle Attivita' Motorie|
Settore MED/09 - Medicina Interna
|Data di pubblicazione:||2013|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1139/apnm-2012-0396|
|Appare nelle tipologie:||01 - Articolo su periodico|