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

Pharyngeal collapsibility during sleep is believed to increase due to a decline in dilator muscle activity. However, genioglossus electromyogram (EMG) often increases during apnoeas and hypopnoeas, often without mechanical effect. 17 patients with obstructive sleep apnoea were anaesthetised and evaluated from termination of propofol administration to awakening. Genioglossus EMG, flow and pharyngeal area (pharyngoscopy) were monitored. Prolonged hypopnoeas enabled evaluation of the relationships between genioglossus EMG and mechanical events, before and after awakening. Additional dilator muscle EMGs were recorded and compared to the genioglossus. Electrical stimulation of the genioglossus was used to evaluate possible mechanical dysfunction. Prolonged hypopnoeas during inspiration before arousal triggered an increase in genioglossus EMG, reaching mean ± SD 62.2 ± 32.7% of maximum. This augmented activity failed to increase flow and pharyngeal area. Awakening resulted in fast pharyngeal enlargement and restoration of unobstructed flow, with marked reduction in genioglossus EMG. Electrical stimulation of the genioglossus under propofol anaesthesia increased the inspiratory pharyngeal area (from 25.1 ± 28 to 66.3 ± 75.5 mm(2); p<0.01) and flow (from 11.5 ± 6.5 to 18.6 ± 9.2 L · min(-1); p<0.001), indicating adequate mechanical response. All additional dilators increased their inspiratory activity during hypopnoeas. During propofol anaesthesia, pharyngeal occlusion persists despite large increases in genioglossus EMG, in the presence of a preserved mechanical response to electrical stimulation.

Interacting effects of genioglossus stimulation and mandibular advancement in sleep apnea.

Both mandibular advancement (MA) and stimulation of the genioglossus (GG) have been shown to improve upper airway patency, but neither one achieves the effect of continuous positive airway pressure (CPAP) treatment. In the present study we assessed the combined effect of MA and GG stimulation on the relaxed pharynx in patients with obstructive sleep apnea (OSA). We evaluated responses of upper airway pressure-flow relationships and endoscopically determined pharyngeal cross-sectional area to MA and electrical stimulation of the GG in 14 propofol-anesthetized OSA patients. Measurements were undertaken at multiple levels of CPAP, enabling calculation of the critical closing pressure (Pcrit), upstream resistance (Rus), and pharyngeal compliance. GG stimulation, MA, and the combination of both shifted the pressure:flow relationships toward higher flow levels, resulting in progressively lower Pcrit (from baseline of 2.9 +/- 2.2 to 0.9 +/- 2.5, -1.4 +/- 2.9, and -4.2 +/- 3.3 cmH(2)O, respectively), without significant change in Rus. DeltaPcrit during GG stimulation was significantly larger during MA than under baseline conditions (-2.8 +/- 1.4 vs. -2.0 +/- 1.4 cmH(2)O, P = 0.011). Combining the effect of GG stimulation with MA lowered Pcrit below 0 in all patients and restored pharyngeal patency to a level that enabled flow above the hypopnea level in 10/14 of the patients. Velopharyngeal compliance was not affected by either manipulation. We conclude that the combined effect of MA and GG stimulation is additive and may act in synergy, preventing substantial flow limitation of the relaxed pharynx in most OSA patients.

[Electrical stimulation of the genioglossus to improve pharyngeal patency in obstructive sleep apnea: comparison of results obtained during sleep and anesthesia].

Contraction of the geniogtossus (GG) has been shown to improve upper airway patency in patients with sleep apnea during sleep and anesthesia. However, a large variability in response exists, requiring selection of adequate patients if GG stimulation should be used as a treatment modality. In the present study, we compared responses in upper airway pressure-flow relationships to electrical stimulation of the GG in patients with obstructive sleep apnea during sleep and mild anesthesia. Nine patients studied during sleep were matched with 9 patients evaluated during propofol anesthesia. Stimulation was performed with fine wire electrodes inserted near the mandibular insertion of the GG. Airflow was measured at muLtiple levels of CPAP, and upper airway collapsibility was defined by the pressure below which airflow ceased (the "critical" pressure, Pcrit). ELectrical stimulation shifted the pressure-flow reLationships toward higher flow Levels in all patients over the entire range of CPAP applied. Pcrit decreased significantly during stimulation-induced contraction of the GG, and similarly in the patients evaluated during sleep and during anesthesia (from 1.6 +/- 2.0 to -1.6 +/- 2.5, and from 1.8 +/- 1.8 to -0.2 +/- 1.8 cmH2O, during steep and anesthesia, respectively, p < 0.01, without a significant change in upstream resistance. Our findings imply that responses in Pcrit to electrical stimulation of the main tongue protrusor during propofoL anesthesia may reflect those observed during sleep, and evaluation of the response of sleep apnea patients to GG stimulation can be evaluated during short anesthesia.

Effect of coactivation of tongue protrusor and retractor muscles on pharyngeal lumen and airflow in sleep apnea patients.

The present study evaluated the effect of coactivation of tongue protrusors and retractors on pharyngeal patency in patients with obstructive sleep apnea. The effect of genioglossus (GG), hyoglossus (HG), and coactivation of both on nasal pressure (Pn):flow relationships was evaluated in a sleep study (SlS, n = 7) and during a propofol anesthesia study (AnS, n = 7). GG was stimulated with sublingual surface electrodes in SlS and with intramuscular electrodes in AnS, while HG was stimulated with surface electrodes in both groups. In the AnS, the cross-sectional area (CSA):Pn relationships was measured with a pharyngoscope to estimate velopharyngeal compliance . In the SlS, surface stimulation of GG had no effect on the critical pressure (Pcrit), HG increased Pcrit from 2.8 +/- 1.7 to 3.7 +/- 1.6 cmH(2)O, but coactivation lowered Pcrit to 0.2 +/- 1.9 cmH(2)O (P < 0.01 for both). In the AnS, intramuscular stimulation of GG lowered Pcrit from 2.6 +/- 1.3 to 1.0 +/- 2.8 cmH(2)O, HG increased Pcrit to 6.2 +/- 2.5 cmH(2)O (P < 0.01), and coactivation had a similar effect to that of GG (Pcrit = 1.2 +/- 2.4 cmH(2)O, P < 0.05). None of the interventions affected significantly velopharyngeal compliance. We conclude that the beneficial effect of coactivation depends on the pattern of GG fiber recruitment: although surface stimulation of GG failed to protrude the tongue, it prevented the occlusive effect of the retractor, thereby improving pharyngeal patency during coactivation. Stimulation of deeper GG fibers with intramuscular electrodes enlarged the pharynx, and coactivation had no additive effect.

Mechanical parameters determining pharyngeal collapsibility in patients with sleep apnea.

The relative impact of mechanical factors on pharyngeal patency in patients with obstructive sleep apnea is poorly understood. The present study was designed to evaluate parameters of the "tube law" on pharyngeal pressure-flow relationships and collapsibility in patients with obstructive sleep apnea. We developed a mathematical model that considered the collapsible segment of the pharynx to represent an orifice of varying diameter. The model enabled us to assess the effects of pharyngeal compliance (C), neutral cross-sectional area (A(o)), external peripharyngeal pressure (P(ex)), and the resistance proximal to the site of collapse on flow mechanics and pharyngeal collapsibility [critical pressure (P(crit))]. All parameters were measured in 15 patients with obstructive sleep apnea under propofol anesthesia, both at rest and during mandibular advancement and electrical stimulation of the genioglossus. The data was used both to confirm the validity of the model and to compare expected and actual relationships between the tube-law parameters and the pharyngeal pressure-flow relationship and collapsibility. We found a close correlation between predicted and measured P(crit) (R = 0.98), including changes observed during pharyngeal manipulations. C and A(o) were closely and directly interrelated (R = 0.93) and did not correlate with P(crit). A significant correlation was found between P(ex) and P(crit) (R = 0.77; P < 0.01). We conclude that the pharynx of patients with obstructive sleep apnea can be modeled as an orifice with varying diameter. Pharyngeal compliance and A(o) are closely interrelated. Pharyngeal collapsibility depends primarily on the surrounding pressure.