Sleep apnoea research. Patient wearing a continuous positive airway pressure (CPAP) mask while sleeping. Electrodes attached to the patient are monitoring brain and heart activity. Sleep apnoea is a condition common in overweight individuals that restricts the patient's airways during sleep. It results in interrupted breathing that frequently wakes the patient. The CPAP machine delivers a constant stream of compressed air to the patient, via the face mask. The pressure from the stream of air keeps the airway open and allows uninterrupted sleep. Photographed at Stanford Sleep Clinic, Palo Alto, California, USA, in 1987.