Spaceflight on the Cardiovascular and Haemostatic System

¶ … Spaceflight on the Cardiovascular and Haemostatic System

Several physiological changes occur during spaceflights, the most noticeable of which are on the cardiovascular and haemostatic system of the body.

Since the human body is adapted to live in a world of gravity, it has developed ways of combating the gravity's downward force. For example, due to the earth's gravity blood tends to accumulate in the lower limbs but the body is equipped with a system to help monitor and maintain the blood flow and pressure so that the upper body and organs get an adequate supply of blood. In the zero gravity environment during spaceflights when there is no downward force, the upper body gets more than its share of blood. This triggers the monitoring receptors which signal to the body to reduce the volume of blood. As blood passes through the kidney, the excess plasma volume is excreted, lowering total blood volume. Other cardiovascular changes relate to changes in the functioning of muscles in the veins, neurotransmitters and the heart. There are tiny muscles in the veins of our legs that contract when the veins are filled with blood, in order to send the blood 'uphill' in normal circumstance. In a zero-gravity environment where there is no 'up-hill' the tiny muscles in the veins and the neurotransmitters are no longer required to function. As a result they seem to 'forget' their normal functioning and when the astronauts return to a normal gravity environment, such 'forgetfulness' causes a shortage of blood flow in the upper body. Changes in the functioning of the heart, including irregular heartbeat, have also been noted during spaceflights of longer duration.