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Comparative Study
. 2022 Jan;21(1):78-83.
doi: 10.1016/j.jcf.2021.08.013. Epub 2021 Aug 31.

A comparison of clinic and home spirometry as longtudinal outcomes in cystic fibrosis

Alex Paynter  1 , Umer Khan  2 , Sonya L Heltshe  3 , Christopher H Goss  4 , Noah Lechtzin  5 , Nicole Mayer Hamblett  6
Affiliations
Comparative Study

A comparison of clinic and home spirometry as longtudinal outcomes in cystic fibrosis

Alex Paynter et al. J Cyst Fibros. 2022 Jan.

Abstract

Background: The COVID-19 pandemic has accelerated the transition to telehealth, including the use of home spirometry in cystic fibrosis. Evaluating the accuracy and precision of longitudinal home spirometry is a requisite for telehealth-based research. This secondary analysis of a CF study (eICE) evaluates whether there are cross-sectional or longitudinal differences between home and clinic spirometry.

Methods: Participants age ≥14 years with ppFEV1>25 were recruited from 2011-2015, issued a home spirometer, and asked to complete spirometry efforts twice per week for one year. Clinic spirometry was collected at baseline and every three months. Cross-sectional differences between clinic spirometry and the closest home spirometry measurement were analyzed. Longitudinally, we apply 5 methods to analyze the precision of home spirometry, and differences between clinic vs. home data.

Results: Home spirometry is estimated to be 2.0 (95% CI: 0.3, 3.5) percentage points lower than clinic spirometry cross-sectionally. Longitudinally, the estimates of 12-month change in home spirometry varied by analysis method from -2.6 to -1.0 ppFEV1/ year, with precision markedly different. However, home spirometry change estimates were qualitatively similar to the clinic results: -3.0 ppFEV1/year (95% CI: -4.1, -1.9).

Conclusions: To leverage the potential cost, feasibility and convenience of home spirometry, the differences with clinic spirometry must be acknowledged. Significantly lower ppFEV1 in home devices shows that direct comparison to clinic spirometers may induce a spurious change from baseline, and additional variability in home devices impacts statistical power. The effect of coaching, setting, and equipment must be understood to use and improve home spirometry in CF.

Keywords: CF outcome measures; COVID-19; Coronavirus; Forced expiratory volume in one second (FEV1); Remote monitoring; Telehealth.

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Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Illustration of all analytic methods on a single participant's home data. The gray line is the participant's home-measured ppFEV1. Clinic visit timing is represented by gray triangles along X-axis. Methods displayed are: NN (nearest neighbor; blue circles), WM (windowed mean; orange bar width indicates the window of home measures utilized), IPR (individual participant regression; green line), MMLT (mixed model linear in time; pink line), and MMST (mixed model with a spline for time; lavender curve). See supplement for additional details. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 2
Fig. 2
A: Estimates of the cross-sectional difference using NN and WM methods, with WM repeated over various window widths (7d, 14d, …). The estimated difference, 95% confidence interval, and the standard deviation of the difference are labeled. B: NN analysis of each visit individually, limited to the subjects who have home and clinic data for all 5 visits (n = 44).
Fig. 3
Fig. 3
Difference versus mean plot (Bland-Altman) for individual home/clinic observation pairs (matching as described for NN method). The mean difference and limits of agreement, ±1.96 times the standard deviation of the difference, are shown. The mean difference differs slightly from Fig. 2 as this is not a mixed model.
Fig. 4
Fig. 4
A: Estimates of change from baseline using clinic spirometry measures (top row) and home measures (bottom row). Methods are shown with 95% confidence bands. B: Forest plot of the change from baseline estimated at 12 months, confidence intervals and standard errors for the change labeled at right. The confidence intervals in 4B are identical to the 12-month change estimates of each plot in 4A.
See this image and copyright information in PMC

Comment in

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