[Significance of electromyography of the diaphragm in respiratory physiopathology]

Adequate electromyographic method are available in order to record the electrical activity of the vertebral (oesophageal surface electrodes) and the right or left costal (concentric needle electrodes) parts of the diaphragm and in order to stabilize the EMG's base line (rejection of the electrical movement's artefacts by means of RC filters). The electromyographic patterns of the agonistic and antagonistic activity of the diaphragm in normal subjects have been clearly defined in different circumstances such as quiet ventilation and hyperventilation. Disturbances of the ventilatory diaphragmatic activity have been demonstrated by electromyography in different diseases: broncho-pneumopathies; supraspinal disorders, myopathies. In normal subjects, global motor responses of the diaphragm to the electrical stimulation of each phrenic nerve can be easily recorded with surface electrodes located in the oesophageal hiatus or placed over the lower intercostal spaces. The phrenic nerve conduction times was measured in 30 normal adults. The average value of this parameter was 7,5 +/- 0,53 msec for excitation on the right side and 8,2 +/- 0,71 on the left. The measurement of the phrenic nerve conduction time seems to provide a sensitive index of involvement of the nerve in diaphragmatic dyskinesias. Prolongation of conduction time was demonstrated in phrenic lesions of various aetiologies such as: peripheral polyneuropathies, traumatic sequelae, mediastinal tumors, phrenic neuritis or idiopathic diaphragmatic paresis. Electrical phrenic stimulation and prostigmin have permitted to establish the diagnosis of myasthenic bloc of the phrenodiaphragmatic transmission.