Expiratory activation of abdominal muscle is associated with improved respiratory stability and an increase in minute ventilation in REM epochs of adult rats

Abstract

Breathing is more vulnerable to apneas and irregular breathing patterns during rapid eye movement (REM) sleep in both humans and rodents. We previously reported that robust and recurrent recruitment of expiratory abdominal (ABD) muscle activity is present in rats during REM epochs despite ongoing REM-induced muscle atonia in skeletal musculature. To develop a further understanding of the characteristics of ABD recruitment during REM epochs and their relationship with breathing patterns and irregularities, we sought to compare REM epochs that displayed ABD muscle recruitment with those that did not, within the same rats. Specifically, we investigated respiratory characteristics that preceded and followed recruitment. We hypothesized that ABD muscle recruitment would be likely to occur following respiratory irregularities and would subsequently contribute to respiratory stability and the maintenance of good ventilation following recruitment. Our data demonstrate that epochs of REM sleep containing ABD recruitments (REM(ABD+)) were characterized by increased respiratory rate variability and increased presence of spontaneous brief central apneas. Within these epochs, respiratory events that displayed ABD muscle activation were preceded by periods of increased respiratory rate variability. Onset of ABD muscle activity increased tidal volume, amplitude of diaphragmatic contractions, and minute ventilation compared with the periods preceding ABD muscle activation. These results show that expiratory muscle activity is more likely recruited when respiration is irregular and its recruitment is subsequently associated with an increase in minute ventilation and a more regular respiratory rhythm.

Hypercapnia‐induced active expiration increases in sleep and enhances ventilation in unanaesthetized rats

“…The observation (i) that active expiration failed to be consistently recruited by hypercapnia in both sleeping and awake rats is consistent with the observation that active expiration was not consistently recruited in REM sleep (Andrews & Pagliardini, ). It seems that factors other than levels of chemical drive and state influence abdominal expiratory activity.…”

“…In contrast, other reports in the literature showed that active expiration is recruited during sleep in rats and humans (Pagliardini et al . ; Andrews & Pagliardini, ; and in our present study). The fact that RTN neurons drive active expiration only during wakefulness suggests that different mechanisms to recruit active expiration may be involved during sleep.…”

“…). Likewise, in unanaesthetized rats in room air, events of active expiration (that lasted for more than three consecutive breaths as defined by the authors) occurred in only ∼49% of REM epochs (147 out of 300 REM epochs) (Andrews & Pagliardini, ). The amount of REM sleep seen in our study was small, suggesting that long‐lasting recording experiments are needed to yield sufficient REM episodes to accurately examine the recurrent activation of ABD EMG activity.…”

“…Interestingly, however, under eupnoeic conditions, where active expiration is absent normally, abdominal activity emerges in the REM‐like sleep state in urethane‐anaesthetized rats as well as in REM sleep, providing stability to breathing (Pagliardini et al . ; Andrews & Pagliardini, ). Evidence of hypercapnia‐induced expiratory abdominal activity in rats extends from in situ preparations (Abdala et al .…”

Cardiovascular and respiratory profiles during the sleep–wake cycle of rats previously submitted to chronic intermittent hypoxia

“…Previous studies, also performed in rats, suggest that active expiration, i.e. expiratory recruitment of abdominal muscles, occurs during both NREM and REM sleep (Andrews & Pagliardini, ; Sherrey, Pollard, & Megirian, ), although it is more frequent after apnoea and high respiratory variability events observed in REM sleep (Andrews & Pagliardini, ).…”