Mechanisms underlying the prolonged activation of the genioglossus following arousal from sleep (original) (raw)
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Journal of Applied Physiology, 2012
It is generally believed that reflex recruitment of pharyngeal dilator muscles is insufficient to open the airway of obstructive apnea (OSA) patients once it is closed and, therefore, that arousal is required. Yet arousal promotes recurrence of obstruction. There is no information about how much dilator [genioglossus (GG)] activation is required to open the airway (GG Opening Threshold) or about the capacity of reflex mechanisms to increase dilator activity before/without arousal (Non-Arousal Activation). The relationship between these two variables is important for ventilatory stability. We measured both variables in 32 OSA patients (apnea-hypopnea index 74 ± 42 events/h). GG activity was monitored while patients were on optimal continuous positive airway pressure (CPAP). Zopiclone was administered to delay arousal. Maximum GG activity (GGMAX) and airway closing pressure (PCRIT) were measured. During stable sleep CPAP was decreased to 1 cmH2O to induce obstructive events and the di...
Genioglossal Activation in Patients with Obstructive Sleep Apnea versus Control Subjects
American Journal of Respiratory and Critical Care Medicine, 2001
Pharyngeal dilator muscle activation (GGEMG) during wakefulness is greater in patients with obstructive sleep apnea (OSA) than in healthy control subjects, representing a neuromuscular compensatory mechanism for a more collapsible airway. As previous work from our laboratory has demonstrated a close relationship between GGEMG and epiglottic pressure, we examined the relationship between genioglossal activity and epiglottic pressure in patients with apnea and in control subjects across a wide range of epiglottic pressures during basal breathing, negative-pressure (ironlung) ventilation, heliox breathing, and inspiratory resistive loading. GGEMG was greater in the patients with apnea under all conditions (p Ͻ 0.05 for all comparisons), including tonic, phasic, and peak phasic GGEMG. In addition, patients with apnea generated a greater peak epiglottic pressure on a breath-by-breath basis. Although the relationship between GGEMG and epiglottic negative pressure was tight across all conditions in both groups (all R values у 0.69), there were no significant differences in the slope of this relationship between the two groups (all p values Ͼ 0.30) under any condition. Thus, the increased GGEMG seen in the patient with apnea during wakefulness appears to be a product of an increased tonic activation of the muscle, combined with increased negative-pressure generation during inspiration.
Phasic electromyographic activity of the genioglossus increases in normals during slow-wave sleep
Respiration Physiology, 1991
Obstructive apneas occur infrequently during Stage 3-4 NREM sleep (SWS), even in patients with severe obstructive sleep apnea. To investigate whether upper airway (UA) dilator muscle activity preferentially increases during SWS as a partial explanation for this phenomenon, we measured phasic electromyogram activity of the genioglossus muscle (EMGgg) during continuous Stage 2 NREM sleep and SWS in 5 healthy males. Subjects were studied supine during a complete cycle of nocturnr' NREM sleep after partial sleep deprivation. EMGgg was measured with perorally inserted bipolar electrodes, and quantified as peak phasic inspiratory activity during all continuous epochs of NREM sleep. We found EMGgg to be increased during SWS relative to stage 2 sleep by a mean of 58% among all subjects (P-0,02); neither end-tidal Pc,, nor inspired minute ventilation varied between these sleep stages. Upper airway resistance, measured in 3 of the subjects on a separate study night, was not different between SWS and Stage 2 sleep. We speculate that the increase in phasic EMGgg during SWS in our normal subjects may reflect a mechanism whereby UA patency tends to be preserved during this stage. Animal, man; Genioglossus muscle; Obstructive sleep apnea; Sleep apnea; Upper airway resistance, during sleep The progression from waking through the stages of NREM sleep has been associated with progressive hypotonia of the upper airway skeletal muscles as well as decreased cortical input to those muscles (Remmers, 1981). However, stage 3-4 NREM sleep (slow-wave sleep, SWS) has been found to be a time of decreased obstructive respiratory events in patients with obstructive sleep apnea (OSA)(Dinner et aL, 1989
The Journal of Physiology, 2007
During wakefulness, obstructive sleep apnoea patients appear to compensate for an anatomically narrow upper airway by increasing upper airway dilator muscle activity, e.g. genioglossus, at least partly via a negative-pressure reflex that may be diminished in sleep. Previous studies have assessed the negative-pressure reflex using multi-unit, rectified, moving-time-average EMG recordings during brief pulses of negative upper-airway pressure. However, moving-time averaging probably obscures the true time-related reflex morphology, potentially masking transient excitatory and inhibitory components. This study aimed to re-examine the genioglossus negative-pressure reflex in detail, without moving-time averaging. Bipolar fine-wire electrodes were inserted per orally into the genioglossus muscle in 17 healthy subjects. Two upper airway pressure catheters were inserted per nasally. Genioglossus EMG reflex responses were generated via negative-pressure stimuli (∼ −10 cmH 2 O at the choanae, 250 ms duration) delivered during wakefulness and sleep. Ensemble-averaged, rectified, genioglossus EMG recordings demonstrated reflex activation (onset latency 26 ± 1 ms; peak amplitude 231 ± 29% of baseline) followed by a previously unreported suppression (peak latency 71 ± 4 ms; 67 ± 8% of baseline). Single-motor-unit activity, clearly identifiable in ∼10% of trials in six subjects, showed a concomitant increase in the interspike interval from baseline (26 ± 9 ms, P = 0.01). Genioglossus negative-pressure reflex morphology and amplitude of the initial peak were maintained in non-rapid eye movement (NREM) sleep but suppression amplitude was more pronounced during NREM and declined further during REM sleep compared to wakefulness. These data indicate there are both excitatory and inhibitory components to the genioglossus negative-pressure reflex which are differentially affected by state.
Discharge Patterns of Human Genioglossus Motor Units during Arousal from Sleep
Sleep, 2010
Study Objectives: Single motor unit recordings of the human genioglossus muscle reveal motor units with a variety of discharge patterns. Integrated multiunit electromyographic recordings of genioglossus have demonstrated an abrupt increase in the muscle's activity at arousal from sleep. The aim of the present study was to determine the effect of arousal from sleep on the activity of individual motor units as a function of their particular discharge pattern. Design: Genioglossus activity was measured using intramuscular fine-wire electrodes inserted via a percutaneous approach. Arousals from sleep were identified using the ASDA criterion and the genioglossus electromyogram recordings analyzed for single motor unit activity. Setting: Sleep research laboratory. Participants: Sleep and respiratory data were collected in 8 healthy subjects (6 men). Measurements and Results: 138 motor units were identified during prearousalarousal sleep: 25% inspiratory phasic, 33% inspiratory tonic, 4% expiratory phasic, 3% expiratory tonic, and 35% tonic. At arousal from sleep inspiratory phasic units significantly increased the proportion of a breath over which they were active, but did not appreciably increase their rate of firing. 80 new units were identified at arousals, 75% were inspiratory, many of which were active for only 1 or 2 breaths. 22% of units active before arousal, particularly expiratory and tonic units, stopped at the arousal. Conclusions: Increased genioglossus muscle activity at arousal from sleep is primarily due to recruitment of inspiratory phasic motor units. Further, activity within the genioglossus motoneuron pool is reorganized at arousal as, in addition to recruitment, ~20% of units active before arousals stopped firing.
Discharge patterns of human genioglossus motor units during sleep onset
Sleep
Study Objectives: Single motor unit recordings of the human genioglossus muscle reveal motor units with a variety of discharge patterns. Integrated multiunit electromyographic recordings of genioglossus have demonstrated an abrupt increase in the muscle's activity at arousal from sleep. The aim of the present study was to determine the effect of arousal from sleep on the activity of individual motor units as a function of their particular discharge pattern. Design: Genioglossus activity was measured using intramuscular fine-wire electrodes inserted via a percutaneous approach. Arousals from sleep were identified using the ASDA criterion and the genioglossus electromyogram recordings analyzed for single motor unit activity. Setting: Sleep research laboratory. Participants: Sleep and respiratory data were collected in 8 healthy subjects (6 men). Measurements and Results: 138 motor units were identified during prearousalarousal sleep: 25% inspiratory phasic, 33% inspiratory tonic, 4% expiratory phasic, 3% expiratory tonic, and 35% tonic. At arousal from sleep inspiratory phasic units significantly increased the proportion of a breath over which they were active, but did not appreciably increase their rate of firing. 80 new units were identified at arousals, 75% were inspiratory, many of which were active for only 1 or 2 breaths. 22% of units active before arousal, particularly expiratory and tonic units, stopped at the arousal. Conclusions: Increased genioglossus muscle activity at arousal from sleep is primarily due to recruitment of inspiratory phasic motor units. Further, activity within the genioglossus motoneuron pool is reorganized at arousal as, in addition to recruitment, ~20% of units active before arousals stopped firing.
SLEEP, 2015
To compare changes in end-tidal CO 2 , genioglossus muscle activity and upper airway resistance following tone-induced arousal and the return to sleep in healthy individuals with small and large ventilatory responses to arousal. Design: Observational study. Setting: Two sleep physiology laboratories. Patients or Participants: 35 men and 25 women with no medical or sleep disorders. Interventions: Auditory tones to induce 3-s to 15-s cortical arousals from sleep. Measurements and Results: During arousal from sleep, subjects with large ventilatory responses to arousal had higher ventilation (by analytical design) and tidal volume, and more marked reductions in the partial pressure of end-tidal CO 2 compared to subjects with small ventilatory responses to arousal. However, following the return to sleep, ventilation, genioglossus muscle activity, and upper airway resistance did not differ between high and low ventilatory response groups (Breath 1 on return to sleep: ventilation 6.7 ± 0.4 and 5.5 ± 0.3 L/min, peak genioglossus activity 3.4% ± 1.0% and 4.8% ± 1.0% maximum, upper airway resistance 4.7 ± 0.7 and 5.5 ± 1.0 cm H 2 O/L/s, respectively). Furthermore, dilator muscle activity did not fall below the pre-arousal sleeping level and upper airway resistance did not rise above the pre-arousal sleeping level in either group for 10 breaths following the return to sleep. Conclusions: Regardless of the magnitude of the ventilatory response to arousal from sleep and subsequent reduction in PETCO 2 , healthy individuals did not develop reduced dilator muscle activity nor increased upper airway resistance, indicative of partial airway collapse, on the return to sleep. These findings challenge the commonly stated notion that arousals predispose to upper airway obstruction.
Journal of Applied Physiology, 2008
Hypoxia can depress ventilation, respiratory load sensation, and the cough reflex, and potentially other protective respiratory reflexes such as respiratory muscle responses to increased respiratory load. In sleep-disordered breathing, increased respiratory load and hypoxia frequently coexist. This study aimed to examine the effects of hypoxia on the reflex responses of 1) the genioglossus (the largest upper airway dilator muscle) and 2) the scalene muscle (an obligatory inspiratory muscle) to negative-pressure pulse stimuli during wakefulness and sleep. We hypothesized that hypoxia would impair these reflex responses. Fourteen healthy men, 19–42 yr old, were studied on two separate occasions, ∼1 wk apart. Bipolar fine-wire electrodes were inserted orally into the genioglossus muscle, and surface electrodes were placed overlying the left scalene muscle to record EMG activity. In random order, participants were exposed to mild overnight hypoxia (arterial oxygen saturation ∼85%) or me...