Mechanisms Producing Ventilatory Periodicities

Abstract

Ventilation is disturbed in sleep even in healthy individuals. In rapid-eye-movement sleep (REMS) disburbances in ventilation are coupled to phasic events. In 10 normal subjects respiratory frequency was found to be positively correlated and rib cage motion was inversely correlated with eye movement density during REMS. Abdominal motion was little affected, and hence the adverse effects of phasic events on overall ventilation were limited. Ventilation during non-rapid-eye movement sleep (NREMS) is characterized by regular periodicities. 'Itro mechanisms are thought to be involved. First, instability of the chemical feedback system caused by high overall loop gain leads to ventilatory oscillations. Second, removal of the wakefulness stimulus leads to reductions in ventilation at sleep onset. It is likely that these two mechanisms interact to produce periodicities in ventilation during early stage 1-2 NREMS. Ventilation is commonly disturbed in sleep. This both occurs in normal individuals, and is particularly severe in patients with sleep apnea syndrome. The mechanisms underlying this are likely to be different in the different stages of sleep. In rapid eye-movement sleep, the disturbances are coupled to the phasic events that occur in this state. One method to measure these phasic events is by recording rapid eye-movements. We have developed a method to examine the interrelationship between ventilation and its components and eye-movements. This method is based on computing separately a running average of ventilation and its components and eye movement density (number of eye movements/second). The window length of the running average, the degree of overlap between adjacent windows and the delay (or lag) between the ventilation and eye movement measures is adjustable. The latter is to allow for asynchrony between the ventilatory changes and the occurrence of eye movements. We have found that a window length of