The Pulmonary Health Index (PHI): A Novel Composite Indicator of Lung Health Status in Patients With Asthma or COPD

Abstract Background When assessing disease impact in patients with Asthma or COPD, clinicians often consider a combination of factors including symptom burden and airflow limitation relative to intensity of maintenance treatment. Although acute exacerbations may influence the natural history of the disease, not all patients experience these infrequent events. We sought to derive a composite indicator of lung health status across the spectrum of obstructive lung diseases utilising readily available clinical measures obtained from patients with physician-assigned asthma or COPD from the NOVELTY cohort [NCT02760329]. Methods We explored three domains: physiological measures, disease-specific quality of life, and treatment intensity. Several variables were assessed for each domain which were prioritised by commonality of measure, clinical relevance and performance against a model of linear disease trajectory. Each variable was weighted to achieve a continuous score of 0-100 (higher value being greater lung health). One-sided Mann-Whitney U tests were performed to assess this score against lung function alone for predicting physician-assigned severity at baseline and exacerbations in the following year. Results The proposed “Pulmonary Health Index” (PHI) is a weighted composite marker comprising percent predicted post-bronchodilator Forced Expiratory Volume in 1 second (ppFEV1), the Chronic Airways Assessment Test (CAAT) and treatment intensity. For differentiating physician-assigned severity, PHI performs at least as well as ppFEV1. We grouped patient data by severity (mild, moderate, severe), diagnosis, and visit year (0, 1, 2, 3) and assessed both PHI and ppFEV1 to differentiate against the null hypothesis. For all 24 tests undertaken, the p-values were below the 0.05 significance threshold. In 5/12 tests for asthma, PHI had lower p-values than ppFEV1. In all other tests, both PHI and ppFEV1 had p < 0.001. For rate of exacerbations in the following 12 months, we confirmed that patients with fewer exacerbations had higher ppFEV1 and PHI values. We grouped patient data by 0, 1, and 2+ exacerbations, diagnosis, and visit year (0, 1, 2). Of the 18 tests undertaken, PHI returned a lower p-value than ppFEV1 in all instances. Whereas ppFEV1 was significant in only 12/18 tests, PHI was significant in 17/18 tests. Conclusion Pulmonary Health Index provides a standardised, holistic indicator of lung health status in patients with asthma or COPD that appears to be superior to ppFEV1 alone. PHI is easily measurable in clinical practice and can be used to determine the disease impact and burden upon an individual patient and to monitor disease progression.