WHO, WHAT, WHY?
The Magazine answers...
David Blaine has just finished his latest stunt - hanging upside down for three days. But what are the effects on the body of upending yourself and can it be dangerous?
Why it's a bad idea to be upside down is all about evolution.
Humans have evolved under the influence of a lifestyle that sees them one way up for the vast majority of every day.
As a result it makes sense that the way the blood is pumped around the body naturally relies on gravity to help.
Putting yourself the wrong way up means it is harder to get blood to the lower limbs and that blood is not easily returned from the head and upper body, with potentially disastrous effects.
Dr Paul Ford, senior lecturer in exercise physiology at the University of East London, cannot think of any type of sportsman who spends prolonged periods of time upside down.
Trapeze artists, rock climbers and bungee jumpers find themselves upside down, but it is rarely for more than a few minutes.
"The main thing is going to be the gravitational effect on blood flow. Normally the heart is supported by the effect of gravity," says Dr Ford.
When blood is being pumped to your feet, gravity helps take it on its way. To get blood to your head your body has evolved to pump harder.
But while there are muscles that help get the blood back from the legs, the brain doesn't have these same muscles. So it doesn't take long before blood begins to pool in places where it shouldn't, like the lungs and head.
"The major concern is about the control of the vascular system," says Professor Ashley Grossman, of Barts Medical School, part of Queen Mary, University of London.
Bats sleep upside down
"We have been designed over a million years to try and control blood pressure in terms of gravity from the top to the bottom. We can all cope in the short term but eventually when the blood starts pooling in the lungs and the head problems occur."
And these problems are bad. In the lungs, the risk is of a pulmonary oedema.
"Fluid will start to ease out of the blood vessels, you can't easily get oxygen, the lungs become rather stiff and you get breathless," says Professor Grossman.
"You might be able to breathe a bit faster but I doubt if that's going to work for more than a few hours before you get exhausted."
But as bad as this fluid on the lungs is, there is a more catastrophic danger for the upside down publicity seeker. The pooling of blood in the brain can cause death.
Harness and platform
"If the blood pressure is too high you are liable to have a stroke," says Prof Grossman.
And it's this danger of death that probably explains why Blaine did not really remain upside down for the whole 60 hours.
He not only regularly reached up towards his feet with the help of a harness, but actually stood the right way up on a platform at least once an hour.
"About once an hour he had to come down for a medical check, to stretch, and to relieve himself, because even David Blaine couldn't do that upside down," said Patrick Smith, of Rubenstein Associates, who have been doing his publicity.
"He has said all along that there would be times when he must get his head above his heart."
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Blaine was apparently warned of the risk of death before he started. Of course, that's not to say he hasn't done himself some damage anyway. Studies of the effects of being upside down for long periods are not exactly abundant.
"Any long-term change in blood circulation can potentially have long-term effects," says Dr Ford.
On the plus side for Blaine, while the US media have reported that blindness could be one of the dangers he faces, they appear to be wrong.
Rob Scott, of the Royal College of Ophthalmologists, an expert in aviation medicine, says there should be no long-term damage to his eyesight from the stunt.