To learn if thoracic electrical impedance tomography (EIT) measurements correlate with pulmonary function test (PFT) results in amyotrophic lateral sclerosis (ALS) patients.

ALS is a motor neuron disorder associated with craniobulbar and respiratory muscle dysfunction. Throughout disease course, PFT data play key roles in monitoring clinical status and planning therapeutic interventions. However, the accuracy of PFT results can be limited by factors including fatigue and incomplete lip seal around the spirometer, a common occurrence in the setting of orofacial weakness. It would therefore be helpful to have an objective measure of lung function that is independent of effort and orofacial strength.

Thoracic EIT could help address this need. In thoracic EIT, painless electrical currents are applied through surface electrodes placed circumferentially around the torso. Resultant surface voltages can be used to calculate a mean value (z metric) that reflects impedance changes between maximum inspiration and expiration over time.

With ALS patients wearing an exercise-like chest band with internal electromyography surface electrodes, EIT information was obtained during the performance of standard slow and forced vital capacity evaluations in upright and supine positions. Correlations were calculated between the EIT (z metric) and vital capacity (VC, %predicted) findings.