Sleep research: apnoea patient linked up to sleep monitoring equipment at Stanford University's sleep clinic in California. Apnoea (temporary cessation of breathing) during sleep is a condition which is rarely dangerous, but which often prevents normal sleep. The patient may stop breathing for more than 20 seconds, but is then wakened by the lack of oxygen & begins breathing again. The breathing apparatus seen here is a CPAP (continuous positive airway pressure) machine, like those used in intesive care units. The machine provides the subject with air at a slightly raised pressure and has been found to prevent apnoea in a number of cases.