Thoracic electrical impedance tomography for assessing progression of pulmonary dysfunction in ALS

Objective: We compared thoracic electrical impedance tomography (EIT) with slow vital capacity (SVC) to determine if EIT could monitor pulmonary function in ALS patients longitudinally. Methods: Of 32 ALS patients and 32 age- and sex-matched healthy controls (HCs) initially enrolled in the Pulmonary Function via Impedance Tomography (PuFIT) study, 22 ALS and 20 HCs returned for a follow-up visit ∼3.9 months later. All participants had thoracic EIT measurements performed simultaneously with standard SVC in upright and supine positions at both visits. EIT data from each measurement were summarized as a single parameter, the impedance-SVC (zSVC), representing an averaged impedance change across both lungs. We assessed alterations over time for both cohorts of participants. Results: Sufficient quality EIT and SVC data were available for 18 of the patients with ALS and 19 HCs. Over time, mean upright SVC significantly declined by 5% in the ALS group and did not change in the healthy group. Supine SVC showed no change in either group. Although mean trajectories of zSVC mirrored mean SVC trajectories in both participant cohorts, changes in zSVC in ALS patients did not reach significance, due to greater variability in the repeated measures. Conclusion: Despite strong cross-sectional correlations to SVC, EIT did not detect a decline in pulmonary function over approximately four months. Increased variability in EIT data explains the lack of sensitivity to change. Technological improvements and special care with electrode placement will be needed for EIT to reach its full potential in longitudinal assessment of pulmonary function in ALS.