Association of airway obstruction, sleep, and phasic abdominal muscle activity after upper abdominal surgery

We recorded nasal gas flow, sleep stage, and abdominal muscle EMG pattern i n 11 patients throughout the night after abdominal surgery, to examine the association between phasic activity- of the abdominal muscles, sleep stage, and flow disturbance. We used a miniaturized data logging system, and obta ined satisfactory records in eight patients. The data were divided into 30- s epochs. Each epoch was classified as either awake or asleep. The epochs w ere also classified for the presence of phasic activity in the external obl ique abdominal muscle, and for evidence of airway obstruction. Association between these features was tested by a quasi likelihood log linear model. V alues given are median (quartiles) for the eight subjects. Sleep occurred f or 62 (46-69)% of the study time. During sleep, inspiratory flow was normal for 69 (48-81)% of the time, whereas during wakefulness, the flow pattern was normal for 51 (28-77)% of the time. Phasic activity was present 16 (12- 25)% of the time during sleep and 24 (19-37)% of the time during wakefulnes s (P<0.001). In the awake state, when breathing was normal, phasic activity was present 16 (11-30)% of the time. When breathing was obstructed, phasic activity was present 38 (25-44)% of the time (P<0.001). These surprising f indings suggest that sleep may be seriously disturbed by airway obstruction , so that a stable sleep state is not reached. We could not confirm previou s findings that disturbed breathing in post-operative patients only occurs during sleep.