Objective
This study was designed to measure the range of normal values of the diaphragmatic latency, central motor conduction time and the extent of right-left agreement after a magnetic stimulation and to measure the parameters of diaphragmatic activity after magnetic stimulation in stroke patients and to compare them with the results of pulmonary function test (PFT).

Method
In seventeen healthy adults and sixteen well-cooperated stroke patients, a magnetic stimulation with 90 mm circular coil (Magstim 200) on cerebral cortex during inspiration and on C7 spinous process, and a transcutaneous electric stimulation of phrenic nerve were performed. An active electrode was attached at 5 cm superior to the tip of the xiphoid process, a reference electrode at chestwall along the midclavicular line at the lower margin of rib cage, and a ground electrode at sternum. Pulmonary function test was checked in the stroke patients.

Results
The latencies of magnetically evoked Compound muscle action potential (CMAP) were 15.1 ms on cortical stimulation, 7.7 ms on cervical stimulation and the central motor conduction time (CMCT) of diaphragm was 7.4 ms in a control group. Normal limits of each parameter were 17.7 ms, 8.9 ms and 9.8 ms in 95% CI and right-left difference of each parameter was not found. In stroke patients, twelve patients showed delayed CMCT or unevokable CMAP, and among them eleven patients showed restrictive pattern in PFT. Patients with delayed CMCT or unevokable CMAP had significantly high risk of restrictive pulmonary dysfunction.

Conclusions
We measured the normal values of evoked response of the diaphragm for cortical and cervical stimulation. In stroke patients, those with delayed CMCT or unevokable CMAP for diaphragm showed higher incidence of restrictive pulmonary dysfunction. Motor evoked potentials of the diaphragm could be used to detect the respiratory dysfunction of central origin.