Cardiovascular System in Space

Abstract

AbstractThe microgravity environment of space is well tolerated by the cardiovascular system over during periods ranging from weeks to several months. In many ways, the heart, peripheral vasculature, and central cardiovascular control system are exposed to fewer challenges in microgravity than on Earth. Consider the simple act of standing upright in the normal gravity field of Earth. Assumption of an upright posture on Earth causes a redistribution of blood volume to the lower parts of the body, resulting in an increase in blood pressure in dependent blood vessels and a decrease in arterial blood pressure above the level of the heart. The cardiovascular system must quickly compensate for these changes by altering the heart rate, the force of contraction of the heart, and the resistance of the blood vessels to maintain enough blood flow to the brain to prevent loss of consciousness. Under weightless conditions, however, there are no postural changes in blood volume and pressure, which greatly reduces the demands placed on the cardiovascular system to maintain homeostasis. Furthermore, moving about in microgravity requires far less energy than required in gravity, which places less demand on the cardiovascular system.During the long term, however, many physiological systems become dysfunctional when they are not required to perform at a normal level. For example, the muscles and bones of a leg immobilized in a cast for a month or two become atrophied and weak. Similarly, the relatively unchallenging environment of microgravity ultimately results in dysfunctional changes in the heart, the vasculature, and the central cardiovascular control system that may have harmful consequences during spaceflight and upon reexposure of the human organism to a gravitational field.For example, many astronauts cannot maintain normal blood pressure and feel dizzy or faint when standing upright immediately following spaceflight, a condition calledorthostatic intolerance. This may impair their ability to get out of a spacecraft quickly should an emergency arise, or to perform meaningful work upon arrival in a gravitational field, for example, after a trip to Mars. There are also reports of rhythmic disturbances of the heart (cardiac arrhythmias) during spaceflight and of loss of muscle mass of the heart (cardiac atrophy). The latter two conditions, though less well documented than orthostatic intolerance, represent potentially life‐threatening alterations in cardiovascular function. Before these problems in are discussed in detail. A brief review of normal cardiovascular physiology is also presented.