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A friend recently passed on a tip for treating cramp. He said I should cup my hands over my nose and mouth and inhale my exhaled breath. It seems to work quite quickly for cramp in my toes. Is that a coincidence or placebo, or is there a rational explanation? Is it likely to work on more than my toes if necessary?

鈥� There is a plausible reason why this may help, although it assumes there was some hyperventilation 鈥� which results in low carbon dioxide levels in the blood 鈥� at the time of the cramps.

Exhaled breath contains more carbon dioxide than ordinary air. Essentially, the act of breathing into cupped hands raises blood CO₂ as you rebreathe this exhaled air.

鈥淩ebreathing exhaled air may help with cramp by increasing carbon dioxide levels in the blood鈥�

Although CO₂ is a waste product of metabolism, it is also essential and controls a number of aspects of human physiology. For instance, it is needed for the normal dilation and relaxation of airways and blood vessels. When CO₂ levels are low, these constrict, which can lead to symptoms such as wheezing and tingling in the hands and fingers.

More pertinent to the question is the role CO₂ plays in muscle activity. Low levels can cause muscle spasms and twitches. As a respiratory physiotherapist, I have been called into hospital emergency departments more than once to treat patients who present as if they are having an epileptic fit when their symptoms are in fact due to a severe case of acute hypocapnia, or low carbon dioxide.

Rachel Garrod
Marbella, Spain

鈥� Although rebreathing exhaled air 鈥� for example in and out of a paper bag 鈥� can increase the level of CO₂ in the blood, breathing into cupped hands would be ineffective. To treat cramp, I recommend stretching the toes in the opposite direction to the cramp and keeping the feet raised.

John Davies
Lancaster, UK

鈥� Cramp can be caused by low levels of available calcium in the blood. Rebreathing exhaled air leads to a tiny rise in blood carbon dioxide, which makes the blood slightly more acidic. This increases the proportion of blood calcium 鈥� which is often bound to negatively charged sites on albumin proteins 鈥� in its free, ionised form. Cramps in fingers and toes will then rapidly improve.

The questioner might have a chronically low level of calcium in the blood, which is most often caused by low vitamin D. Calcium and vitamin D supplementation would then stop the symptoms from happening so often.

Theo Fenton
London, UK

鈥� Attempting to capture a gas in cupped hands is a pretty futile pursuit. But trying to do so may unconsciously alter the breathing, resulting in physiological change to the blood.

The placebo effect might also be involved. Placebos have been shown to positively affect pulse, blood pressure, anxiety, pain perception and fatigue. They shouldn鈥檛 be dismissed just because we don鈥檛 yet know exactly how they work.

David Muir
Edinburgh, UK

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