Neural drive to human genioglossus in obstructive sleep apnoea

Abstract

One postulated mechanism for obstructive sleep apnoea (OSA) is insufficient drive to the upper-airway musculature during sleep, with increased (compensatory) drive during wakefulness. This generates more electromyographic activity in upper airway muscles including genioglossus. To understand drives to upper airway muscles, we recorded single motor unit activity from genioglossus in male groups of control (n = 7, 7 ± 2 events h −1 ) and severe OSA (n = 9, 54 ± 4 events h −1 ) subjects. One hundred and seventy-eight genioglossus units were recorded using monopolar electrodes. Subjects were awake, supine and breathing through a nasal mask. The distribution of the six types of motor unit activity in genioglossus (Inspiratory Phasic, Inspiratory Tonic, Expiratory Phasic, Expiratory Tonic, Tonic and Tonic Other) was identical in both groups. Single unit action potentials in OSA were larger in area (by 34%, P < 0.05) and longer in duration (by 23%, P < 0.05). Inspiratory units were recruited earlier in OSA than control subjects. In control subjects, Inspiratory Tonic units peaked earlier than Inspiratory Phasic units, while in OSA subjects, Inspiratory Tonic and Phasic units peaked simultaneously. Onset frequencies did not differ between groups, but the peak discharge frequency for Inspiratory Phasic units was higher in OSA (22 ± 1 Hz) than control subjects (19 ± 1 Hz, P = 0.003), but conversely, the peak discharge frequency of Inspiratory Tonic units was higher in control subjects (28 ± 1 Hz versus 25 ± 1 Hz, P < 0.05). Increased motor unit action potential area indicates that neurogenic changes have occurred in OSA. In addition, the differences in the timing and firing frequency of the inspiratory classes of genioglossus motor units indicate that the output of the hypoglossal nucleus may have changed.

Recruitment and rate-coding strategies of the human genioglossus muscle

“…To determine the depth and location for the recording electrodes in genioglossus, the local anatomy of the upper airway musculature was examined with ultrasonography (12L highfrequency linear array transducer, Vivid i GE Healthcare, Chalfont St. Giles, Bucks, UK) (14,38,39). The distance from the skin to the inferior margin of the genioglossus and geniohyoid muscles and the lateral width of genioglossus were recorded using an electronic caliper (14).…”

“…4) (38,39). Briefly, all units were classified into tonic or phasic categories, depending on whether they discharged throughout both inspiration and expiration (tonic), or only during either inspiration or expiration (phasic).…”

Dissociation of electromyogram and mechanical response in sleep apnoea during propofol anaesthesia

“…Although the GG is considered to be a single muscle, its fan-like fibre orientation results in different mechanical activity depending on the fibres recruited [34]. Recent studies that have evaluated single motor-units of the GG have shown that this muscle's EMG is composed of several populations of units that are activated differently during breathing [29,43]. These motor units are coordinated by complex premotor networks [29,44] that may be affected by anaesthesia [45].…”

Nerve and Muscle Changes in the Upper Airways of Subjects with Obstructive Sleep Apnea: Structural Basis for the Neurogenic Theory

“…Another characteristic of the UA muscles is the high percentage disproportion of glycolytic fast twitch of type II muscle fibers compared with non-OSA control subjects [12,14,55,[59][60][61][62], a difference that may represent an adaptive response to mechanical strain and/or neuronal activity. In this way, the over expression of N-CAM is suggestive of collateral nerve sprouting, reflected in the hyperinnervation that present these muscles [13].…”