The use of transcutaneous diaphragmatic EMG measurements to assess the efficacy of respiratory effort has been documented.¹ We have applied this technology to assess the efficacy of Nasal CPAP (NCPAP). There are more complicated and invasive methods available to monitor changes in diaphragmatic EMG. ^{2, 3} We have found transcutaneous monitoring a relatively easy, non-invasive and most effective method.

Method:

Two separate biopotential skin electrodes are placed approximately 3 to 5 centimeters apart subcostally on the patient's right anterior chest wall. Each electrode is referenced to the other. Skin impedance is reduced to <10K Ohms by using isopropyl alcohol or a commercially available pumice cleansor prior to electrode placement. A frequency bandwidth of 30 to 60 Hz is used and the signal amplified through an AC amplifier of a chart recorder so that 1 microvolt equals 1mm of pen deflection. A graphic demonstration of the enervation of the diaphragm is produced. ECG artifact is apparent throughout; however, methods of eliminating ECG artifact are available with appropriate integrators and waveform gating, if desired.¹

We measured the duration and amplitude of the background EMG signal in 3 patients before and after NCPAP treatment for treatment of OSA. A decrease in both parameters was demonstrated with CPAP use. We found that the EMG duration decreased .10 to .20 seconds and EMG amplitude decreased 5.81 to 8.14 microvolts in our random sampling.

Discussion:

The upper airway obstruction increased the workload of the diaphragm.³ When obstruction is relieved by NCPAP, the diaphrgmatic EMG signal is reduced, reflecting the reduced workload required for ventilation.

Decreased respiratory work may rest the inspiratory muscles,⁴ thereby apparently reducing the amount of sleep fragmentation which may have been led to by the increased amount of effort related to the occlusion of the upper airway.

Summary:

Transcutaneous diaphragmatic EMG monitoring provides a non-invasive method of assessing the efficacy of NCPAP in reducing the inspiratory workload of the obstructive sleep apneic patient.

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1 O'Brien MJ, Eykern LA, Oetomo SB, Vught HAJ, Transcutaneous respiratory electromyographic monitoring. Critical Care Medicine, 1987, 15:294-299.

2 Bock WJ, Liesegang J., Eine neue methode zur atmungsuberwachung. Biomed Tech, 1971, 16:48.

3 Vincken W, Guilleminault C, Silvestri L, Cosio M, Grassino A. Inspiratory muscle activity as a trigger causing the airways to open in obstructive apnea. Am Rev Respir Dis, 1987, 135:372-377.

4 Ward ME, Corbeil C, GIbbons W, Newman S, Macklem PT. Optimization of respiratory muscle relaxation during mechanical ventilation. Anesthesiology, 1988, 69:29-35