Feature: Rude awakenings
Waking up from sleep is a stressful time for the body: the heart rate accelerates and blood pressure surges. These increases are far in excess of what the body needs to get up and face the day, a puzzle that is being investigated by sleep physiologist Mary Morrell at the National Heart and Lung Institute, Imperial College, London.
Her research aims to help people with a condition called obstructive sleep apnoea, who wake up hundreds of times during the night due to breathing difficulties. They face cardiovascular stresses again and again while ‘asleep’, and are more likely to have high blood pressure. The condition affects 1-4 per cent of middle aged adults, 24-30 per cent of the elderly and 45 per cent of people with congestive heart failure, and is associated with increased death rates in the last group.
In patients with obstructive sleep apnoea, the surges in heart rate and blood pressure when awakening appear to be linked to the levels of oxygen and carbon dioxide in the blood, and to how sensitive people are to changes in these levels. People who are particularly sensitive, such as people with heart failure, may have the highest levels of cardiovascular stress when waking, making the symptoms of their condition more severe.
See also
- Limiting damage from lack of oxygen
- Scientists in cardiovascular harmony
- Genes that control the asymmetry of the heart
- The virtual heart
- The heart in Greek medicine and philosophy
- Cardiovascular disease in Eastern Europe