Chronic hyperventilation could explain ME, irritable bowel syndrome and asthma. Jerome Burne airs the argument
Usually, physiotherapists - brisk, in white coats, massaging joints and backs - are clearly distinguishable from yoga teachers - laid back, in baggy pastels, concentrating on breathing. Which is why Anne Pitman is so unusual. She is a chartered physiotherapist - friendly, no-nonsense, in a white coat - but she teaches people how to breathe.

A bit redundant you might say, rather like teaching fish to swim or dogs to bark, but that's where you'd be wrong. In fact, an estimated 25 per cent of us don't breathe properly and the result is an extraordinary range of medical problems. Breathing too much, or hyperventilation, is increasingly seen as the hidden cause of all sorts of apparently unconnected chronic ailments, from ME and asthma to irritable bowel syndrome and agoraphobia.

Pitman has just set up in the physiotherapy department of the London Clinic in Devonshire Place where, among the bandages and thermal pads, she gets her patients to stretch out, put their hand on their diaphragm and breathe slowly. "Usually by the time people come to me they've done the medical rounds," she says. "They go to their GP with all these vague symptoms like racing heart, tingling fingers, stiff shoulders and insomnia, but no one can find anything wrong, so they are fobbed off with tranquillisers. Then, they start on the specialists, who can't find anything organic either. Often, they've gone on all sorts of weird diets and started worrying about food allergies."

Take 25-year-old Jane, who had just started in a high-powered job where she was expected to be glamorous as well as clever. After a few weeks, she began to sleep erratically and felt anxious and irritable, but put it down to stress at work. A former champion tennis player, she noticed that her fitness level had dropped drastically and she felt increasingly tired and depressed. She was often short of breath, had tingling sensations in her fingers and lips, and lost all interest in sex. The doctor prescribed sleeping pills and an inhaler. She thought she had a virus infection.

But then a physiotherapist who was treating her for a knee injury noticed her breathing rate was fast - 22 breaths a minute when 10 to 14 is normal - and that her pulse was 90 as opposed to 72. She also sighed deeply four times a minute rather than once every five to ten minutes. A programme to slow her breathing down, plus changes to her wardrobe, so she wore clothes that were less tight round her diaphragm, produced a dramatic reduction in her symptoms within two months.

All of which raises the question of what on earth does breathing too fast have to do with feeling tired, tingling lips and the rest? To understand what is going on, you need to rethink all those school biology lessons on lungs. You remember: you breathe in oxygen which diffuses into the blood, and carbon dioxide comes back the other way and is breathed out as a waste product. What is missing from that explanation is that the key gas is carbon dioxide. There is plenty of oxygen in the air, it makes up about 20 per cent, while the percentage of carbon dioxide (CO2) is tiny, less than one per cent. But carbon dioxide is vital for the process of getting the oxygen from the lungs into the blood. The minute sacs where the exchange takes place actually store carbon dioxide and it is here that the problems caused by hyperventilation begin.

CO2 is a very light gas and when you regularly gulp in extra lungfuls of air, it gets pushed out. The occasional sigh or puffing your way through an exercise routine is no cause for worry, but if the air is whistling in at twice the normal rate, round the clock, for months on end, that's when the troubles start. Less CO2 in the blood means your system gradually becomes more alkaline, which is why hyperventilation can have such a range of effects. The early signs are dizziness and pins and needles. Later, as the body tries to reduce the alkalinity, it produces more lactic acid, which in turn leads to feelings of tiredness and depression. Even more dramatic are the effects when the low CO2 levels start making smooth muscles like the heart and arteries constrict.

"Doctors know all about acute hyperventilation, which can happen when someone has a violent shock," says Anne. "He or she breathes faster and feels they are suffocating. Then what you do is to get them to breathe into a paper bag to raise their CO2 levels. But there's still not much awareness of the dramatic effect hyperventilation over a long period can have, which is why these patients are often written off as hypochondriacs or neurotic."

The paper bag treatment points to another little-known feature of the CO2 connection which makes chronic hyperventilation hard to deal with.

Deep in the most primitive part of your brain is a cluster of cells whose job it is to monitor your breathing. When you are not getting enough air it sends out those awful and irresistible messages that say, "Get more air, I'm suffocating." But what this system responds to is not oxygen but CO2. When the level gets too low the alarm goes off. But if you constantly keep the level down by hyperventilation, this breathing thermostat resets itself. Now levels of CO2 that should be regarded as normal seem too low and the message goes out: "Breathe more."

So, learning to breathe properly with Anne can be hard at first, because you are trying to alter a very basic survival system that ignores all your higher reasons and logic and just keeps yelling, "I'm suffocating."

But Anne's patients soon understand that hyperventilation provides a clear and understandable link between something as nebulous as psychological stress and dozens of all-too physical effects. "When we are anxious or worried, our whole system speeds up ready for action, including our breathing," she says. "But just relaxing does not help chronic hyperventilates, because over-breathing feels right for them. You have to re-train them."

And that is what efficient, white- coated physiotherapists are good at.