Rationale: There are limited validated, objective, and minimally invasive techniques for the bedside evaluation of upper airway obstruction (UAO) in sick infants, despite its frequency in pediatric medicine. Prior techniques include pressure-rate product (PRP), a product of esophageal pressure and respiratory rate and phase angles (PAs), a measure of asynchrony between ribcage and abdominal respiratory movements in infants with UAO. The purpose of this study is to validate the PRP and compare it to a previously validated PA in rhesus monkeys.
Methods: Calibrated resistors were applied to the inspiratory limb of 10 anesthetized, intubated, and spontaneously breathing rhesus monkeys (weight 8.7 +/- 2.5 kg). Airway pressure, respiratory rate, PAs, heart rate, and oxygen saturation were recorded. Obstruction was applied in random order as 0, 5, 20, 200, 500, and 1,000 cmH(2)O/L/sec for 2-min periods, the last 15 sec (10-20 breaths) were analyzed for each timeframe.
Results: PA increased significantly at the 200 cmH(2)O/L/sec level but it reached a plateau above 500 cmH(2)O/L/sec. PRP rose progressively and was significantly different at all levels of obstruction. Esophageal pressure change was progressively and statistically significantly different from baseline and each other at 200, 500, and 1,000 cmH(2)O/L/sec (P < 0.001).
Conclusions: In this model of UAO, PRP tracks increasing inspiratory load better than PA. PRP continued to be linear up through the highest inspiratory resistance where the change in PA reached a plateau before the highest load. The assessment of esophageal pressure changes may offer the simplest objective measure of UAO.