 An all night polysomnogram was recorded with a Compumedics E Series digital polysomnograph. After the scalp was prepared, Ag/AgCl electrodes were applied to the scalp according to the International 10-20 System. EEG was monitored from C4-A1, C3-A2, O2-A1 and O2-A1. EOG and EMG were continuously monitored by electrodes placed at the outer canthi and chin respectively. Nasal and oral airflow were monitored using a triple port Thermistor. Respiratory effort was measured by piezoelectric technology employing an abdominal and thoracic belt. Blood oxygen saturation was continuously monitored by pulse oximetry. Heart rate and rhythm were monitored by surface electrocardiography. Anterior tibialis EMG was studied by using surface mounted electrodes placed 5 cm apart on both legs. Body position and snoring level were also monitored.