A robust and novel electrical impedance metric of pulmonary function in ALS patients

OBJECTIVE

Pulmonary function tests (PFTs) are important for assessing respiratory function in amyotrophic lateral sclerosis (ALS) patients. However, weakness of oral and glottal closure, due to concomitant bulbar dysfunction, may result in unreliable PFT values stemming from leakage of air around the breathing tube and through the glottis. In this study, we assessed whether standard thoracic electrical impedance tomography (EIT) could serve as a surrogate measure for PFTs.

APPROACH

Thoracic EIT was performed simultaneously with standard PFTs on seven ALS patients without clinical bulbar weakness (six men and one woman, mean age of 63 years) and ten healthy volunteers (seven men and three women, mean age of 57 years). A raw impedance metric along with more standard EIT measures were computed and correlated with the normalized forced vital capacity (FVC). Additionally, test/re-test metrics and EIT images were analyzed.

MAIN RESULTS

The impedance metric was found to be robust and sensitive to lung activity. We also identified qualitative EIT differences between healthy volunteers and ALS patients, with the ALS images showing greater heterogeneity. Significant correlations with FVC were found for both impedance and EIT metrics in ALS patients (r² = 0.89) and for the impedance metric only in healthy volunteers (r² = 0.49).

SIGNIFICANCE

This suggests that EIT, using our novel impedance metric, has the potential to serve as an alternative technology to standard PFTs for assessing pulmonary function in patients with ALS, offering new metrics of disease status for those with bulbar weakness.

An improved electrical impedance myography (EIM) tongue array for use in clinical trials

OBJECTIVES

Electrical impedance myography (EIM) measurements of the tongue could provide valuable information about bulbar dysfunction in amyotrophic lateral sclerosis (ALS). A prototype tongue depressor EIM array produced gag reflexes. The objectives of this study were to determine the reliability, mean phase values, and tolerability of tongue EIM measurements using a smaller electrode array.

METHODS

Tongue EIM measurements were performed in a total of 31 healthy individuals and four neuromuscular patients with lingual abnormalities. Reliability was assessed by calculating the intraclass correlation coefficient (ICC) and percent difference in addition to performing Bland-Altman analyses. Standard descriptive statistics, including results of a Mann-Whitney test, were also determined.

RESULTS

At the 50 kHz frequency, the ICCs for intra- and inter-rater reliability were 0.76 with 5.17% difference and 0.78 with 5.34% difference respectively. The mean EIM phase values of healthy participants (11.61° ± 1.00°) and patients (9.87° ± 1.28°) were significantly different (p=0.0051). None of the participants experienced gag reflexes or discomfort.

CONCLUSIONS

The small tongue array provided good inter- and intra-rater reliability, could preliminarily distinguish between healthy and diseased muscle, and was well-tolerated.

SIGNIFICANCE

Biomarker information about tongue health could be more comfortably obtained with a smaller EIM array.