Comparison Between Lung Function Parameters Measured Using Home Spirometry and Routine Office Spirometry in Stable Cystic Fibrosis Patients

Rationale: Lung function deterioration is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Spirometry is an important tool for monitoring lung function decline and early detection of exacerbations. The use of tele-services has increased recently and played a pivotal role in healthcare access to the vulnerable populations during the COVID-19 pandemic. The accuracy and reliability of using home spirometry for CF patients remain unclear. We hypothesized that in stable CF patients, lung function measured using home spirometry would correlate with baseline lung function measured by clinic spirometry. Methods: We prospectively enrolled patients with stable CF who received handheld ZEPHYRx® home spirometers from May-December 2020. We analyzed home spirometry efforts that met ATS Standards. Baseline characteristics were retrospectively collected from the electronic health records including baseline lung function-calculated as the average of the best two clinic spirometry efforts, when available. Only home spirometry measurements of patients on stable therapy were included (elexacaftor/tezacaftor/ivacaftor). Pearson's correlation coefficients were performed to evaluate the relationship between baseline lung function and mean home spirometry measures. We measured both point estimates and mean values for home spirometry. Results: We analyzed a cohort of 77 patients, which consisted of 40 (51.9%) females and 76 (98.7%) Non-Hispanic Caucasian. The mean age of patients was 34.3 years (SD 10.9). The average baseline percent predicted FEV1 measured in clinic (FEV1(c)) was 68.7 (SD 23.2) and the average percent predicted FEV1 measured using home spirometry (FEV1(h)) was 66.6 (SD 20.9). The mean baseline percent predicted FVC in clinic (FVC(c)) was 73.5 (SD 21.7) whereas the mean FVC measured using home spirometry (FVC(h)) was 83.5 (SD 18.5). Mean peak expiratory flow rates (PEFR) measured in a subset of patients (n= 48) at baseline in clinic (PEF(c)) was 7.2 l/min (SD 19.1), and mean PEFR measured using home spirometry (PEF(h)) was 7.0 l/min (SD 1.8). A very strong correlation was found between FEV1(c) and FEV1(h) (r = 0.95, P< 0.001). Whereas strong correlations were found between FVC(c) and FVC(h) (r = 0.713, P<0.001) and PEF(c) and PEF(h) (r= 0.895, P<0.001). Conclusion: In a cohort of stable CF patients, the spirometric measures (FEV1, FVC and PEF) using a home spirometry device have stronger or better correlations with the corresponding baseline lung function. Home spirometry is a reliable device in monitoring CF patients. Further studies are ongoing exploring the variability and repeatability of home spirometry measures.