Study: Use Lung Clearance Index to Measure Function
An assessment called the lung clearance index could be used to help identify people with cystic fibrosis (CF) who are at high risk for worsening lung function, a study has found.
The study reported on factors associated with a worsening lung clearance index (LCI) over time in CF patients, which included initial LCI measurements and bacterial infections.
Titled, “Longitudinal assessment of lung clearance index to monitor disease progression in children and adults with cystic fibrosis,” the study was published in the journal Thorax.
LCI is a measurement of how well the lungs are able to take gas in and out. LCI represents the number of lung volume “turnovers” needed for clearance of a tracer gas; a higher value is indicative of worse lung function.
While LCI may provide useful clinical information, it is not used routinely in many places, in part because the assessment can be complex to administer. Another challenge is that questions remain about how this measurement tends to change over time.
In this study, a team led by researchers in the United Kingdom reported data from a prospective study in which LCI was incorporated into routine clinical practice at three specialty centers. In all, the study recruited 122 children and adults with CF, of whom 112 (92%) were able to complete at least one LCI assessment. (Eight participants were unable to complete LCI assessments, and two were withdrawn from the study because they were reclassified as not having CF.)
Because they were interested in how measurements might change over time — in the absence of noteworthy clinical changes — the researchers specifically looked at patients with relatively stable CF.
In a first analysis, the team looked at data from 80 patients who had pairs of LCI readings taken within six months of each other. They conducted statistical analyses to examine the repeatability of LCI, and found that measures could vary from reading-to-reading by about 20%.
“Tighter reproducibility may be seen over shorter time spans or in clinical trials, but for clinical practice this figure therefore seems relatively robust across different age groups and devices,” the scientists wrote.
The team then conducted additional statistical analyses to look at trends in LCI over time, and clinical factors that were associated with those trends. Overall, nearly three-quarters of participants had LCI measurements that were stable over time.
“It was reassuring that the majority of these patients with predominantly mild CF fell into a cohort [group] with stable LCI throughout the course of the study,” the researchers wrote.
Still, other trends were seen in a minority of patients. One in 10 started with LCI measurements about normal, and then the values increased over time (indicating worsening lung function). A similar proportion started with higher-than-normal measurements, which then worsened over time.
In statistical models, the factor most powerfully associated with changes over time was LCI at baseline (at the start of the study). Other significantly associated factors included age, infection with the bacteria Pseudomonas aeruginosa, use of antibiotics, and baseline forced expiratory volume in one second — a measure of lung function based on the amount of air a person can exhale in one second.
According to the researchers, these patients “could serve as interventional groups in future studies.”
In addition to clinical analyses, 18 adults returned surveys on how it felt to undergo LCI. Overall, the procedure was well-tolerated, with most patients saying it was easy to complete. The most common suggested improvement was shortening the time it took to complete the measurement (median of about 20 minutes).
“We have shown that, with the appropriate resources, LCI can be routinely delivered in a clinical setting and is generally acceptable to patients,” the researchers wrote.
Overall, the findings “support the use of LCI in clinical practice in identifying patients at risk of lung function decline,” the team concluded, though they added that “the measurement is challenging to deliver in routine practice and in many cases may be better suited to annual assessments.”