Load detection in subjects with sleep-induced upper airway obstruction.

Respiratory flow-resistive load detection in obese patients has been shown to be impaired. We tested the hypothesis that there is no difference in inspiratory flow-resistive load detection measured in nonobese obstructive sleep apnea patients, nonobese snorers, and normal control subjects. Eleven male obstructive sleep apnea patients and seven male snorers were investigated and compared with 10 normal male control subjects. Severely obese patients (body mass index, BMI > 35 kg/m2) were excluded. Patients were investigated by nocturnal polysomnography with measurement of esophageal pressure (Pes). Awake pulmonary function tests were performed before the investigation. Airway resistance (Raw) and lung volumes were measured with plethysmography. Resistive loads were investigated according to Tapper and associates (13) and Killian and associates (12). Resistances were applied for the duration of one inspiratory cycle and a minimum of two breaths allowed between each resistive load. Six different resistances plus background shams were presented 10 times in random order. Flow, pressure, and subject response were recorded with a calibrated multichannel recorder. Subjects signaled detected changes of inspiratory resistance with a hand-held signaling device. The probability of detecting a particular resistance was calculated as the ratio of correct identification to the number of presentations (i.e., 10). The resistance corresponding to a 0.5 probability of detection was determined. The Weber fraction (wf) calculated as delta R/R(apparatus) +Raw. There were no differences between nonobese subjects and controls in terms of resistive load detection.