NASAL AND PHARYNGEAL RESISTANCE AFTER TOPICAL MUCOSAL VASOCONSTRICTION IN NORMAL HUMANS

Phenylephrine, an alpha-adrenergic agonist, increases pharyngeal cross-sectional area when applied topically to the nasal and pharyngeal mucosa, as determined by magnetic resonance imaging. In this study, we examined the possibility that the increase in area results from either a decrease in transmural collapsing pressure, as a result of a decrease in upstream (nasal) resistance, or an increase in upper airway muscle activity. In eight normal, awake mon we measured inspiratory pharyngeal and nasal resistance and the electrical activity of the genioglossus (EMG(GG)) and alae nasi (EMG(AN)) before and after pharyngeal and nasal + pharyngeal instillation of 1 ml of either 0.25% phenylephrine or normal saline; phenylephrine and saline were tested on separate days. Under control eucapnic conditions, pharyngeal resistance was 0.43 +/- 0.03 CM H2O/L/s, and nasal resistance was 2.43 +/- 0.14 cm H2O/L/s. Pharyngeal resistance was 0.29 +/- 0.03 cm H2O/L/s after nasal + pharyngeal instillation of phenylephrine and 0.98 +/- 0.13 cm H2O/L/s after saline; nasal resistance was 2.18 +/- 0.13 cm H2O/L/s after nasal + pharyngeal instillation of phenylephrine and 3.15 +/- 0.21 cm H2O/L/s after saline. Thus, phenylephrine decreased both nasal and pharyngeal inspiratory resistance. The change in pharyngeal resistance was not dependent on the change in nasal resistance. Eucapnic EMG(GG) and EMG(AN) activities did not change after phenylephrine or saline. We conclude that phenylephrine decreased pharyngeal resistance independent of a change in nasal resistance or upper airway muscle activity, and we believe that the changes in resistance we observed reflect a direct effect of phenylephrine on the pharyngeal mucosa and a consequent enlargement of pharyngeal size. Therefore, mechanisms controlling the volume of the pharyngeal mucosa such as sympathetic vasomotor tone are important in regulating upper airway mechanics in normal humans.