Frequency and significance of increased upper airway resistance during sleep

Previous studies have shown that episodes of inspiratory flow limitation ca n be clinically important. We have challenged the hypothesis that patients with the "upper airway resistance syndrome" have more episodes of inspirato ry flow limitation, associated with greater swings in pleural pressure and more arousals from sleep than normal subjects. We thus studied eight sympto matic patients with UARS (ESS > 10, AHI < 15) and eight matched asymptomati c subjects. All had overnight polysomnography with recording of pleural pre ssure and airflow derived from nasal pressure. Events scored visually using nasal pressure were termed flow limitation events and those using both sig nals "resistive events." The patients with UARS had no more episodes of flo w limitation or resistive events than the controls. However, pleural pressu re swings at resistive event termination were significantly more negative i n the patient group (-15 [IQR 9-19]; -11 [8-12] cm H2O; p = 0.02) and the n umber of cortical arousals associated with resistive events was higher in t he patients (median, 10 [5-75]; 3 [1-9]/h slept; p = 0.02). This study conf irms that patients with UARS have periods of increased upper airway resista nce associated with significant sleep fragmentation. However, resistive eve nts are also common in normal subjects, although these are associated with less negative pleural pressure swings and fewer arousals. Thus, the clinica l significance of resistive events needs to be interpreted with caution.