Aviation and Space Physiology (2)

by Patience Joseph-Mamman

Aviation Physiology.

The speed with which a plane takes off into the sky the acceleratory involved cause some effects on body functions. When a plane makes a turn the force of its centrifugal acceleration is directly proportional to the square of it’s velocity and inversely proportional to the radius of its turn. What this means is the greater the force with which the plane takes off and the sharper the angle with which it turns to take off, the greater the force with which it lifts up into the sky. The centrifugal force that acts during the take off period is two dimensional in relation to the force of gravity.

  1. At take off as the plane begins to rise there seems to be an intense build up in positive gravitational force and this causes the following effects on the body. There is an increased hydrostatic pressure in the feet that causes pooling of blood in the lower limbs. There is also a decrease in cardiac output as a greater quantity of the blood is pooled in the lower body and does not return to the heart. This then triggers blackouts and unconsciousness shortly after.
  2. As the plane begins to stabilize, we notice a fall in the effect of gravitational force leading to what is known as negative gravitational force. As a result of this too, the body experiences the following:
    -when the negative gravitational forces are intense they cause momentary increased blood flow to the brain and hence psychotic disturbances from brain edema.
    -The eyes could also be affected by this sudden surge in blood flow to the head region resulting in a temporary ‘red-out’, a condition in which the blood vessels in the eyes become so engorged with blood that the person experiences temporary blindness.

Space Physiology
Unlike the airplane, a spacecraft cannot make rapid turns therefore centrifugal force of acceleration has very little effect here. However, the blast off acceleration and deceleration forces are also tremendous one being positive and the other negative.

When a spacecraft is taking off its acceleration could be as high as 8G (positive gravitational force). In a standing position the human body cannot withstand this much acceleration and so most times astronauts stay in a semi-reclining position transverse to the axis of the acceleration. This is the reason for their use of reclining seats.

Problems also occur during deceleration as the spacecraft re-enters the atmosphere. The speed with which the spacecraft is travelling which determines it’s deceleration.

A high speed spacecraft travelling at a speed equal to that in interplanetary space travel would require about 10, 000 miles for safe deceleration. As a result human beings can withstand far less deceleration if the period lasts for a long time than a short one. Therefore deceleration must be accomplished much more slowly from high velocities than is necessary at lower velocities.

The Spacecraft Atmosphere.
There is no atmosphere in outer space, an artificial atmosphere and climate must be produced. The oxygen concentration most importantly must remain high enough and the carbon dioxide’s low enough to prevent suffocation. In most space shuttles, they use gases equal to those in normal air are used with 4 times as much Nitrogen as oxygen. The presence of nitrogen in the mixture is to prevent fire explosions. The nitrogen also protects the lining of the lungs against developing patches that could cause total collapse of the lung tissues.

For space travels lasting more than several months, recycling techniques are employed for use of the same oxygen over and over. Some process involves electrolysis of water and sometimes the use of algae to generate oxygen through photosynthesis.

The effect of weightlessness on the body.
A person in non-propelled spacecraft begins to experience weightlessness. This means that the person seems to float around without any force drawing him towards the side or center of the spacecraft. Some of the physiologic effects of these on the body include:
– motion sickness during the first few- motion sickness during the first few days of travel
– translocation of fluids within the body because of failure of gravity to cause hydrostatic pressures.
– diminished physical activity because no strength of muscle contraction is required to oppose the force of gravity.
-Diminished physical activity because no strength of muscle contraction is required to oppose the force of gravity.

There are also prolonged effects of stay in space which include:
– decrease in blood volume.
– decrease in maximum cardiac output.
– decrease in red blood cells mass.
– decrease in muscle strength and work capacity.
– loss of calcium and bone mass.

For this reason, extensive exercise programs are carried out by astronauts during prolonged space laboratory missions, and most of the effects are greatly reduced except for the bone mass loss.

The observed effects of a prolonged stay in space are as follows:
-decrease in blood volume.
-decrease in red blood cell mass
-decrease in muscle strength and work capacity.
-decrease in maximum cardiac out put.
-decrease in loss of calcium and phosphate from the bones as well as loss of bone mass.

For this reason extensive exercise programs are carried out by astronauts during prolonged space laboratory missions and most of the effects are greatly reduced, except for some of the bone loss. In previous space laboratory expeditions in which the exercise programs had been less vigorous, the astronauts had severely decreased work capacities for the first few days after returning to earth. They also had a tendency to faint when they stood up during the first day because of diminished blood volume and diminished effect of arterial blood pressure control mechanisms.

The effects of weightlessness usually reach their maximum within the first few days to few weeks of entering the space environment. After a few weeks all the effects stop except that of bone mass loss whose stimulation for bone deposition has something to do with gravity. Nevertheless with an appropriate exercise program the physiologic effects of weightlessness have not proved to be a serious problem even duringĀ  prolonged space voyages.

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