Thoracic Electric Impedance Tomography Detects Lung Volume Changes in Amyotrophic Lateral Sclerosis

Spirometry is the conventional means to measure lung function in amyotrophic lateral sclerosis (ALS), but is dependent on patient effort and bulbar strength. We aimed to use electric impedance tomography (EIT), an emerging non-invasive imaging modality, to measure dynamic lung volume changes.

Twenty-one patients with ALS underwent sitting and supine spirometry for forced vital capacity (FVC), and sitting and supine EIT. There were 13 patients in the high FVC group (FVC ≥ 80% predicted) and 8 in the low FVC group (FVC < 80% predicted). Additional demographic and clinical data were collected from clinical records.

Only the low FVC group had significant loss of lung volumes in the supine position (R ² = 0.89 and p < 0.001). The supine volume loss measurement at 10 min correlated with sitting (r ² = 0.47) and supine FVC (r ² = 0.36), maximum inspiratory (r ² = -0.44) and expiratory pressures (r ² = 0.36) (MIP and MEP), and the ALS Functional Rating Scale-Revised (ALSFRS-R) dyspnea subscore (r ² = 0.36).

EIT is an emerging alternative to existing measures of lung function in ALS, but without need for patient effort or bulbar strength. Significant losses in lung volume are seen on supine compared to upright position in patients with respiratory dysfunction. Further study is needed to determine relationships to existing clinical measures.