ENHANCEMENT OF SIGNAL QUALITY IN ESOPHAGEAL RECORDINGS OF DIAPHRAGM EMG

The crural diaphragm electromyogram (EMGdi) is recorded from a sheet o f muscle, the fiber direction of which is mostly perpendicular to an e sophageal bipolar electrode. The region from which the action potentia ls are elicited, the electrically active region of the diaphragm (EAR( di)) and the center of this region (EAR(dictr)) may vary during volunt ary contractions in terms of their position with respect to an esophag eal electrode. Depending on the bipolar electrode's position with resp ect to the EAR(dictr), the EMGdi is filtered to different degrees. The objectives of the present study were to reduce these filtering effect s on the EMGdi by developing an analysis algorithm referred to as the ''double-subtraction technique.'' The results showed that changes in t he position of the EAR(dictr) by +/-5 mm with respect to the electrode pairs located 10 mm caudal and 10 mm cephalad provided a systematic v ariation in the EMG power spectrum center-frequency values by +/-10%. The double-subtraction technique reduced the influence of movement of the EAR(dictr) relative to the electrode array on EMG power spectrum c enter frequency and root mean square values, increased the signal-to-n oise ratio by 2 dB, and increased the number of EMG samples that were accepted by the signal quality indexes by 50%.