Physiological Problems Of Weightlessness And Basic Research
Some predictions on the hazards of the weightless conditions which were made jointly with Haber twelve years ago are reviewed in the light of today’s experience and recent advances in basic research. While it is now obvious that weightlessness does not produce overt short term disturbances of the circulation or respiration, questions pertaining to the possible incidence of motion sickness and to chronic effects on the circulation are still open for discussion.
An outline of recent work on the circulatory basis of fluid volume control through intravascular receptors is presented. Originally it was established that the state of filling of the intrathoracic vascular organs has a profound reflex effect on the diuretic response of the kidney mediated through changes of renal hemodynamics, ADH and corticoids. More recent work indicates that by comparison of afferent impulses from many sites of the body with efferent orders to the heart and circulation the CNS performs an evaluation of the “competence” of the heart to deal with the load imposed on the circulation during a day. Loss of “competence” is accompanied by fluid retention, gain by diuresis.
The application of this principle to the state of weightlessness as far as it could be produced in immersion experiments permits the explanation of observed changes in fluid and mineral metabolism which can in turn be related to current concepts of blood volume control.
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