[Study of preganglionic sympathetic single fibers in relation to various physiologic and pathologic stimuli].
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Biomedical subjects
Publications and source records attributed to A Malliani.
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The goal of the study was to characterize the changes in neurovegetative control of the circulation, attending the presumed physiological and psychological stress originated by the isolation and confinement typical of the living condition of space stations, as simulated in a ground based unit, using time and frequency domain analysis. As a secondary goal we sought to verify the implementation of real time data acquisition, for off line spectral analysis of R-R interval, systolic arterial pressure (by Finapres) and respiration (by PVF2 piezoelectric sensors). We addressed the cardiorespiratory and neurovegetative responses to standardized, simple stressors (active standing, dynamic and static handgrip) on the EXEMSI 92 crew, before, during and after the isolation period. On average the appropriate excitatory responses (to stand, dynamic and static handgrip) were elicited also in isolation and confinement. Active standing and small masses muscular exercises are easy to be performed in a confined and isolated environment and provide a valuable tool for investigating the adaptational changes in neural control mechanisms. The possibility there exists of using this time and frequency domain approach to monitor the level of performance and well being of the space crew in (quasi) real time.
In this paper the experimental evidence supporting the hypothesis that excitatory sympathetic reflexes may participate in the tonic control of the cardiovascular system is discussed. Positive feedback pressor sympathetic reflexes can be obtained with physiological distensions of the descending thoracic aorta in conscious dogs with all nerves intact in absence of any pain reaction. These excitatory reflexes interact with supraspinal regulatory mechanisms, inhibitory in nature. A massive excitation of cardiac sympathetic afferents, produced by intracoronary injections of bradykinin, also elicits a pressor reflex, without pain reactions. In the absence of anesthesia and recent surgery, the cardiovascular excitatory reflexes, subserved by sympathetic afferent fibers, can easily prevail. We suggest that negative and positive feedback mechanisms interact continuously to achieve the most adequate neural cardiovascular control.