Strokes: The impact

Princess Margaret: Suffering a new stroke

A stroke occurs because part of the brain is deprived of oxygen either because a blood vessel becomes blocked or bursts.

The resulting effects of the stroke vary enormously depending on which area of the brain is affected.

Strokes can damage the complex system of nerves and muscles that control swallowing.

Food can "go down the wrong way" and get into the lungs causing coughing or choking, and in severe cases chest infections and pneumonia.

Catherine Collins, chief dietician at St Georges Hospital in London said stroke patients often had trouble controlling liquids in their mouths.

Therefore, there was a risk of dehydration unless fluids were actively administered.

She said losing as little as 2% of the body's normal fluid content made patients drowsy or confused.

Problems eating solids can lead to malnutrition and secondary problems such as reduced resistance to infection and pressure sore risk.

Swallowing is tested as soon as the stroke patient gets to hospital.

Neurologist Professor Peter Sandercock, a stroke expert from the University of Edinburgh, told the BBC: "Patients are normally tested at the bedside.

"If swallowing really is a problem then what we would do is a clinical x-ray, giving them a fluid which appears dark on x-ray.

"Then we can see if they cannot swallow or if fluid is going down the wrong way."

If there are problems, the patient can be fed by mouth, by a tube going into the nose and down to the stomach, or directly into the stomach.

When problems do not clear up in a few days, patients are assessed by speech and language therapists and dieticians.

Treatment options

When stroke patients are admitted to hospital, they receive acute stroke care.

Treatment is based on test results.

Patients are likely to be asked to make lifestyle changes, such as giving up smoking, cutting back on alcohol, losing weight, reducing cholesterol and doing more exercise.

Doctors may also prescribe aspirin or cholesterol or blood pressure lowering drugs.

Tests are also carried out to see if the arteries in the neck are narrowed, which could mean patients need surgery.

Professor Bath said modern medicine had "quite a potent package" to treat strokes.

Once you have had one stroke, Professor Bath said the chances of having a second one within five years stand at around 40% - or 15 times the risk of someone who has not had a stroke.