Inhaled Volume as a Digital Biomarker Predicting Outcomes in Chronic Respiratory Disease

Inhaler-based digital biomarkers can be objectively evaluated to indicate changes in response to therapeutic interventions. In chronic respiratory disease (CRD), measures of exhaled airflow play a central role in diagnosis and management, yet inhaled measures have not. Digital inhalers can passively collect inspiratory parameters such as inhaled volume (InhV) and peak inspiratory flow (PIF) during real-life patient use. Emphasis has been directed to the PIF, but little is known about the role of the InhV. InhV has now been observed to decrease prior to an exacerbation of asthma or chronic obstructive pulmonary disease and increase afterwards and be lower in uncontrolled asthma patients. These observations are consistent with the current understanding of the pathophysiology of CRD, whereby a strong correlation between InhV and forced expiratory volume in one second has been observed. Measurement of InhV has demonstrated accuracy and low variability, supporting the validity of interpreting individualized trends over time. After counseling, patient inhalation technique decays over time, and it is InhV that decreases more than PIF. Together, these findings suggest that InhV, captured by a digital inhaler, has utility as an effective digital biomarker to aid management of patients with CRD, with InhV being a major factor in the predictive value with respect to acute exacerbations.