DYNAMICS OF PERIODIC BREATHING AND AROUSAL DURING SLEEP AT EXTREME ALTITUDE

To determine whether nocturnal periodic breathing (PB) at altitude is due primarily to unstable control of ventilation or the inability to m aintain stable sleep states, we performed visual and computer analyses of the electroencephalographic and respiratory records of healthy vol unteers at simulated altitudes of 4572, 6100 and 7620 m. Transient aro usals were associated with < 52% of the apneas identified; thus, the P B cycle was not always associated with transient arousal. Following th e termination of oxygen breathing, the reinitiation of PB was not depe ndent on the occurrence of arousal as the primary event. The transitio n from apnea to breathing preceded the appearance of arousal by simila r to 1 to 4 sec. Ventilatory drive in the breaths immediately followin g arousal was significantly larger than corresponding control breaths, matched for Sa(O2) Our findings suggest that altitude-induced PB is u nlikely to result from primary fluctuations in state. Arousals promote the development of PB with apnea and help to sustain these episodes, but are not necessary for their initiation.