Sleep state effects on breathing after spinal cord transection and vagotomy in the cat

Sleep apnea syndrome in chronic spinal cord injury: associated factors and treatment

OBJECTIVE

To determine the prevalence of sleep apnea in a sample of persons with chronic spinal cord injury (SCI) of varying injury levels and degrees of impairment.

DESIGN

Cross-sectional study.

SETTING

Inpatient SCI rehabilitation unit.

PARTICIPANTS

Twenty men with SCI (motor complete and incomplete; American Spinal Injury Association classes A-D) of at least 1 year's duration, randomly selected from patients with SCI undergoing elective hospitalization.

MAIN OUTCOME MEASURES

Apnea index, determined by sleep study (including chest wall movement, airflow, oxygen saturation), and daytime sleepiness, determined by Epworth sleepiness score.

RESULTS

Eight subjects (40%) had sleep apnea, manifested by elevated apnea index (mean +/- SD, 17.1 +/- 6.9) and excessive daytime sleepiness. Sleep apnea was commonly diagnosed in motor-incomplete injuries. A trend (p = .07) existed toward a greater prevalence of sleep apnea with tetraplegia. Age and body mass index were not associated with sleep apnea.

CONCLUSION

The prevalence of sleep apnea in men with chronic SCI admitted for nonrespiratory elective hospitalization is high relative to the general population.

Upper airway dilating muscle hyperactivity during non-rapid eye movement sleep in English bulldogs

Sleep-disordered breathing (SDB) is seen during rapid eye movement (REM) sleep in English bulldogs, but it is absent during non-REM sleep. The SDB during REM sleep is associated with changes in neural drive to the diaphragm (DIA) and to an upper airway dilator, the sternohyoid (SH). In the present study, the EMG activity of the DIA was recorded in unrestrained, naturally sleeping, English bulldogs (n = 6) and in control dogs (n = 5). The EMG of the SH was recorded in five of these bulldogs and in four of the control dogs. The activity of the DIA was similar in the two groups of dogs throughout sleep, with the normal increased variability and altered recruitment patterns during REM sleep in all dogs. However, in the presence of the narrowed upper airway of bulldogs, the pattern of the upper airway dilator was dramatically different. In bulldogs, SH activity was virtually always related to inspiration (96 to 100% of breaths during both waking and non-REM sleep). In contrast, SH activity showed inspiratory-related increases in only a minority of breaths during non-REM sleep (32%) in control dogs (p < 0.05). Furthermore, SH drive, as measured by the plateau amplitude, fell during REM sleep in bulldogs, whereas it increased in control dogs (p < 0.05). In control dogs without SDB, we found that central respiratory drive to the SH was highest but variable during waking and minimal during non-REM sleep and that it fluctuated with phasic events during REM sleep. In bulldogs, however, high levels of SH activity occurred during waking and throughout non-REM sleep, apparently preventing SDB in these states. Episodic decreases in SH drive were observed during REM, and they were associated with SDB. These data support the proposition that compensatory pharyngeal dilator hyperactivity is necessary to maintain airway patency and normal breathing in bulldogs, a canine breed with an anatomically compromised upper airway.

Phasic respiratory muscle patterns and sleep-disordered breathing during rapid eye movement sleep in the English bulldog

Basic mechanisms of sleep-disordered breathing (SDB) during rapid-eye-movement sleep (REMS) have been little investigated, despite the fact that events are often more prolonged and SaO2 nadirs lower during REMS. We predicted that the mechanisms of SDB in REMS would be related to the normal phasic changes in respiratory control in that state, rather than to cyclic arousals or responses to hypoxia as postulated for non-REMS SDB. Recordings of the EMG of the diaphragm (DIA) and the sternohyoid (SH), an upper airway dilating muscle, were made in five English bulldogs during sleep. We found that, as predicted, SDB events were associated with phasic influences rather than with arousals or response to hypoxia. The onset of SDB was significantly related to suppression of drive to both the DIA (p less than 0.01) and the SH (p less than 0.01). The mean drive of the DIA was suppressed to 42% of normal and of the SH to 17% of normal; the suppression of the SH was significantly greater than that of the DIA (p less than 0.05). Events were associated with changes in respiratory muscle EMG patterns typical of phasic REMS (p less than 0.01 for each muscle). The occurrence and duration of events exhibited no clear pattern or relationship to arousal or SaO2. Rather, as would be expected of phenomena associated with phasic REMS, the onset and termination of events were unpredictable. The association of SDB in REMS with phasic REMS influences rather than arousal or hypoxia suggests new directions for therapeutic approaches.

Respiratory effects of the N-methyl-D-aspartate (NMDA) antagonist, MK-801, in intact and vagotomized chronic cats

The effects on respiration of MK-801, an N-methyl-D-aspartate (NMDA) non-competitive antagonist, were studied in awake chronic cats by means of the plethysmographic technique. MK-801 (0.01-3.0 mg/kg) was first given i.v. in cumulative doses. The protocol was repeated 10-15 days later in the same animals after bilateral vagotomy. MK-801 selectively increased the duration of inspiration, causing an apneustic respiration but had no effect on the duration of expiration. The maximal inspiratory duration brought about by MK-801 in the intact cat (4.3 s; control 0.9 s) increased 4-fold after bilateral vagotomy (16.4 s; control 1.7 s). Such results suggest that the termination of the inspiratory phase in normal awake cats results from an interaction of pulmonary vagal afferent inputs (inactive on NMDA receptors) with a central mechanism in which NMDA-type glutamate receptors are activated by dicarboxylic amino acid neurotransmission.

Sleep-related apneic and apneustic breathing following pneumotaxic lesion and vagotomy

Sleep-wakefulness state was found to be a crucial determinant of respiratory pattern in chronic cats with bilateral lesions of the rostral pontine pneumotaxic complex (PC). Lesions resulted in increased TE, TI, and VT in all sleep and waking states. Several state-specific respiratory effects were also observed: (1) comparatively eupneic breathing during alert wakefulness (WI); (2) greatly increased TE in slow wave sleep (SWS); (3) decreased TE during rapid eye movement sleep (REM), relative to SWS; (4) increased tendency for prolonged TI (brief apneusis) during REM. Bilateral vagotomy at 2-5 weeks after PC lesion exaggerated these effects and caused distinct apneusis during REM. The results confirm that the PC is not essential for the occurrence of either rhythmic breathing or for expression of state changes in respiration, although the effects of the PC on breathing in the intact cat may vary as a function of sleep-wakefulness state. It is suggested that other regulatory systems that influence the central respiratory rhythm generator (RRG) are similarly modulated by state, and that variations in respiratory pattern observed following PC lesion and vagotomy are the result of state-dependent changes in the balance between multiple inputs to the RRG.