At-Home Versus in-Clinic Vital Capacity Measurement: Insights From the HEALEY ALS Platform Trial

Respiratory weakness, typically monitored as vital capacity (VC), is a central feature of amyotrophic lateral sclerosis (ALS). VC is increasingly measured remotely in participants' homes, although in-clinic assessment remains the standard. We tested concordance between at-home and in-clinic VC to determine trial eligibility, track progression, and predict survival in a large ALS trial.

At-home and in-clinic VC were assessed at baseline and approximately every 8 weeks for a year in the first four regimens of the HEALEY ALS Platform Trial. At-home assessments were coached via live videoconference and centrally reviewed. VC measurements, expressed as percent of predicted normal (%PN), were compared cross-sectionally, longitudinally, and for predicting survival time. Data from 233 participants with 3-8 paired at-home and in-clinic VC assessments completed < 14 days apart were analyzed.

At-home and in-clinic VC were well correlated (Lin's r _c  = 0.82) with no systematic bias. At-home VC ≥ 60%PN predicted in-clinic VC ≥ 60%PN with a positive predictive value of 91% and a negative predictive value of 65%. VC slopes were moderately correlated (r _c  = 0.68). At-home VC progressed 28% faster than in-clinic VC with proportionately less variance (at-home [SE] = -1.882 [0.153] %PN/month, in-clinic = -1.476 [0.131] %PN/month). Slopes of at-home and in-clinic VC explained 15% and 17% of variation in future survival time, respectively.

At-home and in-clinic VC were well correlated cross-sectionally. At-home VC performed well tracking longitudinal change and predicting survival. The reduced participant burden of assessment and concordance with in-clinic measurement support use of at-home monitoring of VC.