Cyclic alternating patterns and arousals: what is relevant in obstructive sleep apnea? In Memoriam Mario Giovanni Terzano

Abstract

Purpose of reviewTo review main knowledges and gaps in the field of sleep microstructure, represented by the cyclic alternating pattern (CAP), in obstructive sleep apnea (OSA). Recent findingsThe (electroencephalographic and autonomic) 'intensity' of arousals in OSA patients, measured through the metrics of CAP, correlate with OSA severity and with disease burden. Continuous positive airway pressure determines variations in sleep architecture (conventional parameters) and at the microstructural level, at different time points. SummaryCAP is not only an 'attractor' of arousals, but also organizes distribution of K-complexes and delta bursts in non-rapid eye movement sleep. Although attention is always concentrated on the A-phase of CAP, a crucial role is play by the phase B, which reflects a period of transient inhibition. Respiratory events in OSA are a typical example of phase B-associated condition, as they occur during the interval between successive A-phases. Accordingly sleep microstructure provides useful insights in the pathophysiology and estimation of OSA severity and may be exploited to follow-up treatment efficacy. In the complex relationship among sleep fragmentation, excessive daytime sleepiness, cognition and cardiovascular risk the CAP framework can offer an integrative perspective in a multidisciplinary scenario.

Effects of CPAP Treatment on Electroencephalographic Activity in Patients with Obstructive Sleep Apnea Syndrome During Deep Sleep with Consideration of Cyclic Alternating Pattern

“…The specificity of CAP is mainly provided by phase A and all phase A subtypes have been shown to be capable of reinstatement of breathing, since respiration recovering after the offset of apneic period of OSA occurred with all phase A subtypes, with the strongest effect nonetheless noted during phase A3 subtype. 11,14 Increased CAP can be induced by the conditions that induce vigilance instability such as noise, insomnia, interictal EEG paroxysms, nocturnal seizures, and periodic leg movements. 35 While CAP phase A (especially A3) is always accompanied by respiratory compensation, this is due to the fact that the CAP phase A with a desynchronized pattern (i.e.…”

“…Apnea in all CAP-related respiratory events is strongly associated with phase B, while phase A is associated with respiratory compensation. 14 Severe OSA patients were found to have fewer CAP subtype A1 and more CAP subtype A3, and CPAP treatment was found to increase the percentage of CAP subtype A1 and decrease the percentage of CAP subtype A3. 11 Two-process model postulates that the propensity to sleep and sleepiness is controlled by the interaction of process S (homeostatic stress of sleep) and process C (circadian rhythm).…”

“…12 The CAP is related to cerebral activities during NREM sleep and is reciprocally influenced by ongoing autonomic and muscle activity, which might determine the pathophysiology of several sleep disorders and the effect of medication and continuous positive airway pressure (CPAP) treatment of OSA. 13,14 The fraction of EEG activity without CAP for more than 60 s consecutively is scored as non-CAP (NCAP) and coincides with a condition of sustained physiological stability. CAP, as a prominent feature parameter in sleep, provides a powerful assessment of brief and frequent arousals.…”

Sleep apnea pathophysiology

“…Findings from the EEG tracings reveal that apneic episodes occur exclusively during inhibitory B-phases; the resumption of breathing correlates with an activating A-phase pattern [24,32,33]. Apneic episodes are never detected during CAP A-phases.…”

“…Apneic episodes appear often, but not always, immediately after phase A during the B-(inhibitory) phase of the CAP [24,32,33] (Fig. 5).…”