The role of vascular tone in the control of upper airway collapsibility

Upper airway collapsibility may be influenced by both muscular and nonmuscular factors. Because mucosal blood volume (and therefore vascular tone) is an important determinant of nasal airway patency, vascular tone may be an important nonmuscular determinant of pharyngeal collapsibility. This hypothesis was tested in two experimental models. First, upper airway closing (CP) and opening (OP) pressures and static compliance were measured in nine anesthetized, sinoaortic-denervated, paralyzed cats with isolated upper airways. Vascular tone was decreased with either papaverine or sodium nitroprusside (NTP), and increased with phenylephrine (PE), whereas blood pressure and end-tidal CO₂ were maintained constant. Vasodilation increased CP (control = -10.4 ± 1.3, NTP = -7.3 ± 1.2 cm H₂O; p < 0.05) and OP (control = -7.9 ± 1.5, NTP = -3.3 ± 1.8 cm H₂O; p < 0.05). In contrast, vasoconstriction tended to decrease CP (control = -10.7 ± 1.5, PE = -11.7 ± 1.4 cm H₂O; p < 0.09) and OP (control = -8.1 ± 1.2, PE = -9.9 ± 1.9 cm H₂O; p < 0.1). Thus, vasodilation increased and vasoconstriction tended to decrease upper airway collapsibility. Upper airway static compliance was unchanged during either drug infusion. In order to assess changes in pharyngeal cross-sectional area (CSA) that occurred during vasodilation, magnetic resonance imaging was utilized in seven cats. During vasodilation with NTP, pharyngeal CSA was reduced from 0.44 ± 0.10 to 0.30 ± 0.09 cm² (p < 0.05), and pharyngeal volume was reduced from 15.3 ± 2.4 to 13.9 ± 2.7 cm³ (p < 0.05). The decrease in pharyngeal caliber was largely attributable to increased thickness of the posterolateral pharyngeal mucosa. Vascular tone appears to be an important nonmuscular determinant of upper airway collapsibility.