In giraffes, the difference in arterial wall size from the upper to the lower body is greater than in any other animal because of their tremendous height. In the microgravity environment of space, this relative difference in artery size isn't necessary because gravity is no longer pulling blood into the lower body. Instead, the blood and other fluids shift upward in the body of animals in space and the cardiovascular system reacts by attempting to balance the relative sizes of blood vessels in the lower and upper body. Scientists don't know the answers to these questions. Another unusual animal studied by NASA Life Sciences Division is the bat.
Bats spend much of their lives hanging upside down.
This reverses the system that most animals have, with the result that bats have thinner blood vessels in the upper body and thicker blood vessels in the lower body. Biologists are interested in knowing how the cardiovascular system of bats overcomes the gravity effect of fluid build-up in the head, seemingly without having problems of elevated intracranial pressure. These and many other questions need to be answered and much work remains to be done. One way to study the effects of microgravity is to be submerged in a large tank of water. Inside this tank people can experience neutral buoyancy and simulated weightlessness.