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  • Cardiovascular re-adjustments and baroreflex response during clinical reambulation procedure at the end of 35-day bed rest in humans
    Adami, Alessandra ...
    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 (P; pressure profiles integral mean), stroke volume (SV; obtained with Modelflow method), and cardiac output (Q; 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 Q stable in both groups until the second minute of standing. Afterward, in INT, P precipitated without further HR increases: SV stopped being corrected and Q reached 2.9 0.4 Lmin(-1) at the last 15 s of standing. Sudden drop in P allowed identification of a low-pressure threshold in INT (70.7 12.9 mm Hg), after which syncope occurred within 80 s. During Recovery, baroreflex curves showed a flat phase (P increase, HR stable), followed by a steep phase (P increased, HR decreased, starting when P was 84.5 12.5 mm Hg and Q was 9.6 1.5 Lmin(-1)). INT, in contrast with tolerant subjects, did not sustain standing because HR was unable to correct for the P drop. These results indicate a major role for impaired arterial baroreflexes in the onset of orthostatic intolerance
    Type of material - article, component part
    Publish date - 2013
    Language - english
    COBISS.SI-ID - 2396627