Hillary Clinton’s stumble at a 9/11 anniversary ceremony last Sunday may have been pounced on by her critics, but many also pointed out that she still managed to fulfil her obligations despite suffering from pneumonia.
The knees buckling, as Clinton’s did, is a classic symptom of fainting. Weak and wobbly legs might seem to be caused by the reduction in blood pressure that often results in fainting. But, in fact, this lack of oxygen being pumped around the body does not affect the limbs directly. Instead, it’s a reaction sparked by the brain to ensure its own survival, as limited oxygen supply is so dangerous. If the brain is starved of oxygen for more than a minute or two it is irreversibly damaged.
While fainting carries the risk of hitting your head, evolution has judged a potential knock to be less dangerous than the threat of oxygen starvation. So, the brain sends a signal to the leg muscles to stop working. This gets the head closer to the level of the heart quickly, where less pumping effort is needed to receive a life-saving supply of blood. Ironically this is exactly the kind of tough call a future commander in chief might be called upon to make.
Dr Daniel Glaser is director of Science Gallery at King’s College London
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