Pharyngeal muscle contraction modifies peri-pharyngeal tissue pressure in rabbits

We examined the influence of pharyngeal dilator muscle activity on upper airway extraluminal tissue pressure (ETP) distribution and upper airway patency. We studied seven anaesthetised, supine, spontaneously breathing NZ white rabbits. ETP was measured via pressure transducer tipped catheters in lateral (ETPlat) and anterior (ETPant) pharyngeal wall tissues. Airflow (V) and tracheal pressure (P) were monitored and upper airway resistance (RUA) calculated. Genioglossus (GG) or bilateral sternohyoid (SH) muscles were electrically stimulated. Tongue protrusion (TP) during GG stimulation was measured. With GG stimulation, RUA decreased to 57.8 ± 10.9% (mean ± S.E.M.) of baseline and TP increased to 4.8 ± 0.5 mm (both p < 0.05), but ETPlat (2.6 ± 1.5 cm H2O) and ETPant (1.4 ± 0.8 cm H2O) were unchanged. SH stimulation reduced RUA to 53.6 ± 6.8%, and ETPlat fell by 1.0 ± 0.4 cm H2O (both p < 0.05). ETPant was unchanged. GG muscle contraction decreased RUA without altering ETP, whereas SH contraction altered RUA and ETPlat, but not ETPant. Contraction of the upper airway dilator muscles results in improvements in upper airway patency associated with changes in peri-pharyngeal tissue pressure.