EFFECT OF BLOOD-PRESSURE CHANGES ON AIR-FLOW DYNAMICS IN THE UPPER AIRWAY OF THE DECEREBRATE CAT

Background: Previous studies suggest that upper airway neuromuscular a ctivity can be affected by changes in blood pressure via a barorecepto r-mediated mechanism. It was hypothesized that increases in blood pres sure would increase upper airway collapsibility predisposing to airway obstruction at a flow-limiting site in the hypopharynx. Methods: To e xamine the effect of blood pressure on upper airway function, maximal inspiratory air now was determined through the isolated feline upper a irway before, during, and after intravenous infusion of phenylephrine (10-20 mu g . kg(-1). min) in six decerebrate, tracheotomized cats. In spiratory now, hypopharyngeal pressure, and pressure at the site of ph aryngeal collapse were recorded as hypopharyngeal pressure was rapidly decreased to achieve inspiratory now limitation in the isolated upper airway. Pressure-now relationships were used to determine maximal ins piratory air flow and its mechanical determinants, the upper airway cr itical pressure (a measure of pharyngeal collapsibility), and the nasa l resistance upstream to the site of flow limitation. Results: An incr eased mean arterial blood pressure of 71 +/- 16 mmHg (mean +/- SD) was associated with significant decrease in maximal inspiratory air how f rom 147 +/- 38 ml/s to 115 +/- 27 ml . sec(-1) (P < 0.01). The decreas e in maximal inspiratory air flow was associated with an increase in u pper airway critical pressure from -8.1 +/- 3.8 to -5.7 +/- 3.7 cm H2O (p < 0.02), with no significant change in nasal resistance. When bloo d pressure was decreased to baseline by discontinuing the phenylephrin e infusion, maximal inspiratory air flow and upper airway critical pre ssure returned to their baseline values. Conclusions: Increased blood pressure Increased the severity of upper airway air how obstruction by increasing pharyngeal collapsibility. Previous studies relating baror eceptor activity to neuromuscular regulation of upper airway tone, are consistent with this effect being mediated by afferent activity from baroreceptors. These findings warrant further study because they sugge st the possibility that upper airway obstruction in postoperative pati ents could either be caused or exacerbated by an increase in blood pre ssure.