Learning from giraffes

Press, 2 December 1987, Page 20

Learning from giraffes

From the “Economist,” London

Giraffes survey the world from a commanding height, which makes them an intriguing object of study themselves. Because they are so tall the effect of gravity on their bodies stands out.

So an international team of scientists led by Dr Alan Hargens from N.A.S.A.’s Ames Research Centre near San Francisco went to South Africa to find out more. One thing the team learnt from giraffes is why astronauts faint and have puffy legs when they come back from long trips in space.

A giraffe’s heart is about two and a half metres above its feet, and its head is two metres higher still. This means the heart has to pump hard to force blood up to the brain, and that gravity pulls plenty of blood down into the legs. Both these things raise the blood pressure in veins and squeeze fluid out of them. The fluid can pool in tissues and puff up the feet — a condition called oedema. This is harmful because it hinders the flow of nutrients from blood to tissue. When blood is in the head, gravity will guide it to the heart. But when it is in the feet, gravity pulls it back. So to get blood from the feet back to the heart, mammals use a system of valves. Every time a mammal moves, skeletal muscles contract and soueeze the blood in nearby veins. But this system will work nniv when a giraffe is using its muscles. If it legs are still — it is nibbling the leaves off

trees, for example — fluid could collect in the tissues. Giraffes use several tricks to avoid this. They have blood vessels with thick walls that trap large molecules and thus help to keep fluid out of tissues. They also have especially tight skins which squeeze their tissues from all sides and thus force fluid that has sneaked into tissues back to the veins. But the best trick used by giraffes — and other mammals too, though giraffes do it especially well — is to squeeze the arteries that lead down to the feet. Giraffes have plenty of muscles ringing their arteries which they can contract to control the flow of blood. To find out more about the muscles, the team examined baby giraffes who had died at birth. There are plenty of these because it is a long drop into the world for giraffes. They found that baby giraffes have only a small amount of arterial muscle and that it is evenly distributed around the body. Adult giraffes, on the other hand, have much more muscle around arteries that are close to the ground. How does it get there? It seems that a new-born giraffe has less muscle because it has been floating in the womb — which is as close to living in zero-gravity as any earth-bound animal comes. The case of giraffes suggests that arterial muscles grow because of gravity rather than because of genes. As Russian doctors know from their

studies of cosmonauts, long stays in space destroy skeletal muscle. What N.A.S.A. learnt from giraffes implies that astronauts will lose arterial muscles, too — if they are deprived of gravity for long. Their muscles will waste away until they are like a baby giraffe’s. This helps to explain why cosmonauts faint and get oedema after long missions. When they return from space, their withered arterial muscles cannot cope with the force of gravity. It will pull blood away from the head and down to the feet. The answer may be for astronauts to use some bizarre training equipment for a few hours each day while they are in space. One idea is to put the astronaut into an airtight bag reaching up to his stomach and then suck out the air inside the bag. This pulls blood down into the lower half of the body — rather like filling an oldfashioned ink pen.

Another idea is to lie him on a rotating beam with his feet sticking outwards. Like a conker pulling on a string when it is whirled round, it would seem to the astronaut as though he were being pulled outwards. While he was behaving like a rotating conker, the blood would rush from his head to his feet, and thus recreate conditions on earth.

Well, in some respects, anyway.'

Copyright — The Economist