Remote FEV1 Monitoring in Asthma Patients: A Pilot Study

Abstract

Forced expiratory volume in one second (FEV₁ ) is a critical parameter for the assessment of lung function for both clinical care and research in patients with asthma. While asthma is defined by variable airflow obstruction, FEV₁ is typically assessed during clinic visits. Mobile spirometry (mSpirometry) allows more frequent measurements of FEV₁ , resulting in a more continuous assessment of lung function over time and its variability. Twelve patients with moderate asthma were recruited in a single-center study and were instructed to perform pulmonary function tests at home twice daily for 28 days and weekly in the clinic. Daily and mean subject compliances were summarized. The agreement between clinic and mobile FEV₁ was assessed using correlation and Bland-Altman analyses. The test-retest reliability for clinic and mSpirometry was assessed by interclass correlation coefficient (ICC). Simulation was conducted to explore if mSpirometry could improve statistical power over clinic counterparts. The mean subject compliance with mSpirometry was 70% for twice-daily and 85% for at least once-daily. The mSpirometry FEV₁ were highly correlated and agreed with clinic ones from the same morning (r = 0.993) and the same afternoon (r = 0.988) with smaller mean difference for the afternoon (0.0019 L) than morning (0.0126 L) measurements. The test-retest reliability of mobile (ICC = 0.932) and clinic (ICC = 0.942) spirometry were comparable. Our simulation analysis indicated greater power using dense mSpirometry than sparse clinic measurements. Overall, we have demonstrated good compliance for repeated at-home mSpirometry, high agreement and comparable test-retest reliability with clinic counterparts, greater statistical power, suggesting a potential for use in asthma clinical research.

Figure 1

Comparison of forced expiratory volume in one second (FEV₁) model residual between mobile spirometry (mSpirometry), and clinical measurements. The FEV₁ model residual is the deviation of each FEV₁ value from the subject’s mSpirometry or clinic average FEV₁ value.

Figure 2

The comparison of mobile spirometry (mSpirometry) and clinic forced expiratory volume in one second (FEV₁) measurements in terms of correlation (a, b) and Bland–Altman (c, d) analyses. Panels a and c describe the morning FEV₁ values and panels b and d describe the afternoon/evening FEV₁ values. The black solid line on panels a and b is the 45‐degree diagonal line that crosses the origin denoting perfect agreement; the dashed purple line indicates the observed linear relationship between mSpirometry and clinic FEV₁ measurements. The solid black line on panels c and d is the zero horizontal line denoting no mean difference; the dashed purple line indicates the observed mean difference between mSpirometry and clinic FEV₁ measurements; and the dotted purple lines indicate the upper and lower bounds of 95% limits of agreement between mSpirometry and clinic FEV₁ measurements.

Figure 3

Empirical power to detect a treatment effect on forced expiratory volume in one second (FEV₁) with two‐sided significance level of 0.05 from 500 simulations under four simulation scenarios (indicated by four colors). The red line shows the power of the “standard” scenario using only one baseline and one treatment period clinic measurements. The green line shows the power of the “multi‐visit” scenario using measurements from all clinic visits after screening. The blue line shows the power of the “once‐daily” scenario using all of the morning (6–10) mobile spirometry (mSpirometry) measurements. The purple line demonstrates the power of the “dense” scenario using all available mSpirometry measurements.