PALATAL MUSCLE EMG RESPONSE TO NEGATIVE-PRESSURE IN AWAKE SLEEP APNEIC AND CONTROL SUBJECTS

The sleep apnea/hypopnea syndrome (SAHS) affects 1-4% of the middle-ag ed population and is caused by repeated occlusion of the upper airway mainly at the retropalatal level. It is unclear why SAHS patients obst ruct their upper airways during sleep while others do not. We hypothes ized that upper airway dilator muscle function may be impaired in SAHS patients and that chronic CPAP therapy may enhance upper airway funct ion. We, therefore, examined the effects of upper airway negative pres sure on reflex palatal muscle activity in 16 normal nonsnoring awake m ale subjects and 16 awake SAHS patients using electromyography. The ap plication of negative upper airway pressure (0 to -12.5 cm H2O) caused increases in levator palatini (LP, p < 0.001) and palatoglossus (PG, p < 0.001) activity, 100 msec after pressure stimulus in normal subjec ts. Application of upper airway negative pressure in SAHS patients cau sed an increase in LP activity (p < 0.05) but not in PG activity. Refl ex electromyographic response to negative pressure was reduced in SAHS patients compared to normal subjects for both muscles (p < 0.001). Wh en the seven thinnest SAHS patients were compared with seven normal su bjects matched for BMI and age, the SAHS patients still demonstrated i mpaired responses to negative pressure for both muscles (p < 0.001). A further eight SAHS patients were studied either while concurrently ta king nightly CPAP therapy and also off CPAP (at least 3 nights). Chron ic nightly CPAP therapy improved the reflex response of both LP (p < 0 .001) and PG (p = 0.003) to nasal negative pressure application. Thus, untreated SAHS patients have impaired electromyographic responses to negative upper airway pressure suggesting impaired defence of the uppe r airway, which is improved by nightly CPAP therapy.