The influence of alcohol on genioglossus single motor units in men and women during wakefulness

Abstract

Alcohol worsens obstructive sleep apnoea (OSA). This effect is thought to be due to alcohol's depressant effect on upper airway dilator muscles such as the genioglossus, but how alcohol reduces genioglossal activity is unknown. The aim of this study was to investigate the effect of alcohol consumption on genioglossus muscle single motor units (MUs). Sixteen healthy individuals were studied on two occasions (alcohol: breath alcohol concentration ∼0.07% and placebo). They were instrumented with a nasal mask, four intramuscular genioglossal EMG electrodes, and an ear oximeter.They were exposed to 8-12 hypoxia trials (45-60 s of 10% O 2 followed by one breath of 100% O 2 ) while awake. MUs were sorted according to their firing patterns and quantified during baseline, hypoxia and recovery. For the alcohol and placebo conditions, global muscle activity (mean ± SD peak inspiratory EMG = 119.3 ± 44.1 and 126.5 ± 51.9 μV, respectively, P = 0.53) and total number of MUs recorded at baseline (68 and 67, respectively) were similar. Likewise, the peak discharge frequency did not differ between conditions (21.2 ± 4.28 vs. 22.4 ± 4.08 Hz, P = 0.09). There was no difference between conditions in the number (101 vs. 88, respectively) and distribution of MU classes during hypoxia, and afterdischarge duration was also similar.In this study, alcohol had a very minor effect on genioglossal activity and afterdischarge in these otherwise healthy young individuals studied while awake. If similar effects are observed during sleep, it would suggest that the worsening of OSA following alcohol may be related to increased upper airway resistance/nasal congestion or arousal threshold changes.

Alcohol and airway calibre: Does motor or muscle depression contribute to increased likelihood of obstruction?

“…A composite of the four recordings allowed for the estimation of global genioglossal activity, whereas spike sorting was used to discriminate motor units from different tongue regions, with motor units classified into standard predetermined categories related to the respiratory cycle. Surprisingly, Avraam et al (2023) found only modest, non-significant effects of alcohol consumption on global genioglossal EMG activity.…”

“…Therefore, studies of the effects of alcohol on genioglossus EMG and motor unit activity throughout the sleep-wake cycle in healthy participants and people with OSAS are warranted. Notwithstanding the findings of Avraam et al (2023), evidence that alcohol consumption worsens the severity of OSAS counsels that a 'nightcap' is contraindicated in people at risk of obstructive airway events and is probably best avoided even by others!…”

“…Studies in animals (Vecchio et al, 2010) and humans (Krol et al, 1984) have demonstrated that alcohol decreases tongue (genioglossus) EMG activity, revealing an inhibitory influence on motor control of upper airway muscles, which might relate to direct actions on cranial motor neurons innervating the tongue and/or depression of supramedullary excitatory inputs to cranial (hypoglossal) motor neurons. In this issue of Experimental Physiology, Avraam et al (2023) describe, for the first time, the influence of acute alcohol ingestion on subpopulations of genioglossus motor units in healthy human participants, with an expectation that differential effects on subclasses of units would be revealed.…”

“…Surprisingly, Avraam et al. ( 2023 ) found only modest, non‐significant effects of alcohol consumption on global genioglossal EMG activity. Moreover, although a decrease in inspiratory motor unit activity was expected, the number of active phasic inspiratory motor units was found to increase after alcohol consumption, which, it is argued, might have arisen from a potential increase in airway resistance attributable to alcohol‐related nasal congestion.…”

“…In this issue of Experimental Physiology , Avraam et al. ( 2023 ) describe, for the first time, the influence of acute alcohol ingestion on subpopulations of genioglossus motor units in healthy human participants, with an expectation that differential effects on subclasses of units would be revealed.…”