Effects of phrenic stimulation on upper airway resistance in anesthetized dogs

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Abstract
Effects of changes in the balance of forces, produced by chest wall and upper airway muscle contraction on upper airway patency, were evaluated in 10 spontaneously breathing anesthetized dogs. Bilateral phrenic nerve stimulation (PNS) was performed in-phase and out-of-phase with spontaneous upper airway muscle contraction, while inspiratory upper airway resistance (Rua) was monitored as an index of airway patency. Airflow (.ovrhdot.V) was measured from a pneumotachograph mounted on an airtight muzzel placed over the animal''s nose and mouth. Upper airway pressure (Pua) was measured as the differential pressure between 1 catheter placed inside the muzzle and another in the sublaryngeal trachea (Rua = peak Pua/peak inspiratory .ovrhdot.V). Alae nasi (AN) electromyogram was monitored as an index of upper airway muscle activation. Compared with spontaneous unstimulated breaths, Rua rose from 1.53 .+-. 0.6 to 4.9 .+-. 0.7 (means .+-. SE) cm H2O .cntdot. l-1 .cntdot. s during PNS in-phase with the AN EMG (P < 0.01); during PNS out-of-phase with the AN EMG, Rua further increased to 10.2 .+-. 1.5 cm H2O .cntdot. l-1 s (P < 0.01). Spontaneous AN EMG was reduced or abolished by i.v. thiopental. During PNS after thiopental infusion, Rua increased to 44.7 .+-. 17.0 cm H2O .cntdot. l-1 s (P < 0.01). During PNS, simultaneous electric stimulation of the ceratohyoid muscles or manual lifting of the hyoid bone restored airway patency and reduced Rua to values near those found during spontaneous unstimulated breaths (P < 0.01). Rua is increased by augmented diaphragm contraction and/or diminished inspiratory upper airway muscle contraction. The region of the hyoid arch may be a critical area for flow resistance in the upper airway.

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