Lung Function Not Closely Linked to Walking Ability in IPF

Severely reduced lung function is not closely related to walking ability in people with idiopathic pulmonary fibrosis (IPF), a new study indicates.

The findings also point to a need to include patients with severely reduced lung function in IPF clinical trials, researchers said.

The study, “Idiopathic pulmonary fibrosis patients with severe physiologic impairment: characteristics and outcomes,” was published in Respiratory Research.

According to researchers, there is a lack of a widely accepted system for rating the severity of IPF. Often, IPF disease severity is measured based on physiologic impairment — that is, reduced lung function. However, it is not clear whether greater physiologic lung impairment corresponds to less ability to function, or specifically, to a reduced walking ability, in these patients.

In the new study, researchers from Inova Fairfax Hospital in Virginia evaluated clinical records of IPF patients treated at their institution in order to better understand the relationship between severe physiologic impairment and functional ability in people with IPF.

Such severe impairment was defined as a forced vital capacity (FCV) of 50% or less and/or a diffusing capacity of the lungs for carbon monoxide (DLCO) of 30% or less. FVC is a measure of lung function based on how much air a person can breathe out in one breath; DLCO measures how well the lungs can absorb oxygen.

The records of 531 IPF patients, treated at referral service between 2011 and 2019, were evaluated, with 185 of them meeting the criteria for severe physiologic impairment at their first appointment. An additional 57 patients progressed to severe physiologic impairment over the course of follow-up and were added to the analysis. That resulted in a total pool of 242 patients, with a mean age of 72, with severe physiologic impairment.

As a measurement of physical function, the researchers evaluated the patients’ six minute walk test (6MWT) scores. As the name suggests, 6MWT is the distance a person can walk in six minutes; it is commonly used as a metric for physical function in people who can walk.

Most (59%) of the patients with severe physiologic impairment required supplemental oxygen during their 6MWT. These individuals walked significantly shorter distances, on average, than those who did not require supplemental oxygen — 281 vs. 337 meters, or 922 vs. 1,106 feet. Patients requiring supplemental oxygen also had significantly lower DLCO, though FVC did not vary significantly based on the need for supplemental oxygen during the 6MWT.

Various statistical analyses found no significant correlation between 6MWT and both FVC and DLCO — in other words, reduced lung function was not predictive of 6MWT scores in a statistical sense.

“We describe a wide range in distances walked highlighting the discordance between severe physiologic and functional impairment,” the researchers wrote. “The fact that 41% of these ‘severe’ patients did not require supplemental oxygen to complete their 6MWTs was somewhat of a surprise which further emphasizes this discordance.”

“Our findings challenge the common belief that patients with severe physiological disease have similarly severe functional impairment,” the team added. “We therefore believe that functional ability and need for supplemental oxygen need to be accounted for and taken into consideration when assessing disease severity.”

Further analyses assessed the relationship between various clinical factors, including FVC and DLCO, and transplant-free survival. In these analyses, male sex and FVC below the median (47% or less) were associated with significantly worse transplant-free survival. In contrast, treatment with antifibrotic therapies — namely Ofev (nintedanib) and/or Esbriet (pirfenidone) — was associated with significantly better transplant-free survival.

“We demonstrate through our outcomes analysis that IPF patients with severe physiologic impairment are at high risk for other meaningful events including hospitalization, need for lung transplantation and death,” the researchers wrote.

The team noted, however, that individuals with severe physiologic impairment are often excluded from IPF clinical trials, due to the idea that, in these individuals, the disease has already progressed to the point that treatment will not be of much help.

“Our analysis, however, provides a rationale to include patients with more severe physiological impairment in future clinical trials,” the researchers wrote.

The team hopes “that this report will embolden investigators and clinical trialists to include more severe patients in future clinical trials of antifibrotic therapy. It is only through a more inclusive approach that future therapies will be made available for this subgroup of IPF patients, who currently lack, and are in most dire need of, therapeutic options.”

Limitations of this study include its retrospective nature, as well as the fact that certain measurements — such as imaging of the lungs — were not assessed.