Functional changes cardiovascular: Normobaric activity and microgravity in young healthy human subjects

Department of Heart and Great Vessels "A. Reale", School of Medicine, Sapienza University of Rome, Italy.
European review for medical and pharmacological sciences (Impact Factor: 1.21). 03/2012; 16(3):310-5.
Source: PubMed


The cardiovascular system works to maintain homeostasis through a series of adaptive responses to physiological requirements. Different self-regulatory mechanism prevent the effects induced by hydrostatic pressure changes on oncotic pressure caused by postural changes. Gravity exerts a strong influence on the postural changes with implications on the cardiovascular system. In orbit, gravity (+Gz) is responsible of mass redistribution of circulating blood flow. The aim of this study was the evaluation of the adaptive responses of cardiovascular system to postural changes with and without the use of the Lower Body Negative Pressure (LBNP). We considered that pressure changes that occur in human body in orbit can be simulated experimentally with use of Tilt-Test (Clino/ortho; Clino/head-down; head-down/ortho). This investigation could be useful for studying the influence on astronauts of long flights.
We studied in 12 months, 30 young healthy volunteers (20 males, 10 female) during postural change tests. In the first evaluation they were submitted to tilt-test for 40 minutes, remaining in head-up +60 degrees (this state corresponds to a kind of gravitational stress +Gz) and in head-down to -30 degrees (-Gz) for 20 minutes. During the second assessment (after 5 +/- 1 days) all volunteers wear a device that simulate a state of LBNP at -20 mmHg. Afterwards, they were processed to 20 minutes in Head Down -8 degrees and after 2 hours of rest to 20 minutes at -15 degrees. Volunteers were monitored measuring blood pressure, heart rate and by Transthoracic Echocardiogram (TTE).
Collected data were elaborated by a statistical analysis. We observed during orthostatic position for 40 min (+60 degrees) without LBNP, lower diameters and volumes of left and right ventricular (p < 0.05) and an increase in heart rate in comparison with the baseline conditions in clinostatism. Despite the reduction of preload volume, the mean value of cardiac output does not vary significantly. In Trendelemburg (-15 degrees) data show a non-significant variation (p > 0.05) of left and right ventricular diameters and volumes, while cardiac output and systolic blood pressure varies significantly (p < 0.05) compared to clinostatic and orthostatic position. With LBNP in head down to -8 degrees and -15 degrees, systolic and diastolic arterial pressure, ventricular volumes and cardiac output were unchanged if compared to values obtained in clinostatism with and without LBNP. If compared to -30 degrees in Trendelemburg without LBNP, data reached statistical significance (p < 0.05).
The cardiovascular system and the autonomic nervous system, respond to postural changes and to volemia alterations, maintaining the physiological cardiac output, in order to preserve the metabolic requirements of body.

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    ABSTRACT: Although changes to visual acuity in spaceflight have been observed in some astronauts since the early days of the space program, the impact to the crew was considered minor. Since that time, missions to the International Space Station have extended the typical duration of time spent in microgravity from a few days or weeks to many months. This has been accompanied by the emergence of a variety of ophthalmic pathologies in a significant proportion of long-duration crewmembers, including globe flattening, choroidal folding, optic disc edema, and optic nerve kinking, among others. The clinical findings of affected astronauts are reminiscent of terrestrial pathologies such as idiopathic intracranial hypertension that are characterized by high intracranial pressure. As a result, NASA has placed an emphasis on determining the relevant factors and their interactions that are responsible for detrimental ophthalmic response to space. This article will describe the Visual Impairment and Intracranial Pressure syndrome, link it to key factors in physiological adaptation to the microgravity environment, particularly a cephalad shifting of bodily fluids, and discuss the implications for ocular biomechanics and physiological function in long-duration spaceflight.
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