Home spirometry has become increasingly used among cystic fibrosis patients during the COVID-19 pandemic, and new research suggests that home devices perform reasonably well. Forced expiratory volume in 1 second (FEV1) values were a bit lower than values seen in clinical spirometry performed in the same patient at a nearby time point, but the procedure reliably picked up decreases in FEV1, potentially helping patients and clinicians spot exacerbations early.
“Home spirometry was sort of a curiosity that was slowly working its way into cystic fibrosis research in 2019, and then all of a sudden in 2020 it became front and center as the only way to continue with clinical monitoring and research in many cases,” Alexander Paynter, MS, a biostatistician at the Cystic Fibrosis Foundation’s Therapeutic Development Network Coordinating Center, said during a talk at the virtual North American Cystic Fibrosis Conference.
To better determine how closely home spirometry matches clinical spirometry, Mr. Paynter and his colleagues analyzed data from the eICE study, which included 267 cystic fibrosis patients aged 14 and over at 14 cystic fibrosis centers. They were randomized to use home spirometry as an early intervention to detect exacerbations, or to continue usual clinic care with visits to the clinic every 3 months. The dataset includes twice-weekly home spirometry values, with a full-year of follow-up data. The researchers compared the home spirometry data to the clinical data closest in time to it. Clinic spirometry data with no corresponding home data within 7 days were discarded.
There was an estimated difference of –2.01 mL between home and clinic tests, with home spirometry producing lower values (95% confidence interval, –3.56 to –0.45). “There is actually a bias in home spirometry as compared to clinic spirometry,” concluded Mr. Paynter.
One explanation for lower values in home spirometry is that users are inexperienced with the device. If that’s true, then agreement should improve over time, but the researchers didn’t see strong evidence of that. Among 44 patients who completed five clinical visits, there was a difference of –2.97 (standard deviation [SD], 10.51) at baseline, –1.66 at 3 months (SD, 13.49), –3.7 at 6 months (SD, 12.44), –0.86 at 9 months (SD, 13.73), and –0.53 at 12 months (SD, 13.35). Though there was improvement over time, “we don’t find a lot of evidence that this bias completely resolves,” said Mr. Paynter.
In fact, a more likely explanation is the presence of coaching by a technician during clinical spirometry, according to Robert J. Giusti, MD, clinical professor of pediatrics and director of the Pediatric Cystic Fibrosis Center at New York University. “When they’re doing it at home, they don’t do it with the same effort, so I think that coaching through telemedicine during the home spirometry would make that difference disappear,” he said when asked to comment on the study.
Dr. Robert J. Giusti
The researchers found that change-based endpoints were similar between clinic and at-home spirometry. Compared to baseline, the two showed similar declines over time. “The clinic and home observations tend to track each other pretty well. At 6 months, for instance, it’s about a change of three points decrease (in both). But the bad news is that the variability is much greater in home devices,” said Mr. Paynter, noting larger confidence intervals and standard deviation values associated with home spirometry. That could influence future clinical designs that may rely on home spirometry, since a larger confidence interval means reduced power, which could double or even quadruple the number of participants needed to achieve the required power, he said.
But from a clinical standpoint, the ability of home spirometry to consistently detect a change from baseline could be quite valuable to future patient management, according to Dr. Giusti. “It looks like home spirometry will show that kind of a decrease, so that it’s still sensitive to pick up the concern that a patient is getting worse at home,” he said.
That could be useful even after the COVID-19 pandemic passes, as patients continue to embrace home monitoring. Physicians could keep track of patients and keep them focused on their care and treatment through frequent telemedicine visits combined with home spirometry. “I really think home spirometry will keep us more focused on how the patients are doing and make for better outcomes,” said Dr. Giusti.
Mr. Paynter and Dr. Giusti have no relevant financial disclosures.
SOURCE: Alex Paynter et al. NACFC 2020. Poster 643.