[Respiratory effort assessed by surface diaphragm EMG in patients with sleep apnea]

Measurement of esophageal pressure is considered to be the gold standard for assessing respiratory effort and neural respiratory drive but this requires placement of an esophageal catheter. We hypothesized that neural drive could be reflected by the diaphragm EMG recorded from chest wall surface electrodes.

We simultaneously recorded esophageal pressure and the chest wall diaphragm EMG in 11 patients with suspected obstructive sleep apnea/hypopnea syndrome during full night polysomnography. We also recorded the diaphragm EMG from esophageal electrode in 5 of the 11 subjects.

Diaphragm EMG could be satisfactorily recorded from 9 of the 11 subjects. The root mean square of the chest wall diaphragm EMG increased gradually during the obstructive sleep apnea events and reached a maximal value at arousal. Similarly, the esophageal pressure increased gradually over the obstructive sleep apnea events and reached a maximal value at the end of apnea. There was a relation between the RMS of the diaphragm EMG recorded from the chest wall surface electrodes and esophageal pressure (r = 0.66) and the diaphragm EMG (r = 0.72) recorded from esophageal electrode during obstructive event.

The diaphragm EMG could be recorded from the chest wall surface electrodes in most subjects and can be used to demonstrate the presence of respiratory effort during apnoea/hypopnea events.