Predicting the Course of Progressive Pulmonary Fibrosis With FOT

Forced oscillation technique (FOT) may be a useful tool to predict the course of progressive pulmonary fibrosis (PPF), a new report has found.

Forced oscillation technique is seen as less strenuous and potentially more suitable for patients with severe pulmonary fibrosis.

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PPF refers to a subtype of patients with interstitial lung disease (ILD) whose fibrosis worsens over time. Early identification is critical in order to identify possible therapeutic interventions.

In a new study in Scientific Reports, corresponding author Anna Denis, MD, of the University Hospital of Liège, in Belgium, explained along with colleagues that the current diagnosis process for PPF relies on conventional pulmonary function tests (PFTs), which measure absolute decline in forced vital capacity (FVC) and predicted or absolute decline in diffusing lung capacity of carbon monoxide (DLCO).1 However, they noted that both measurements can be difficult for certain patients because they require adequate breath and sufficient patient cooperation.

One possible solution, they wrote, is FOT, a quick and noninvasive technique originally developed for obstructive lung diseases.

“Pressures waves are applied at the mouth through a mouthpiece (with a nose clip in place), sur-imposing sinusoidal oscillations to spontaneous tidal breathing at different frequencies (in a range of 5 to 40 Hz),” the authors explained.

A transducer measures air flows and pressures, which can be used to better understand the mechanical properties of the patient’s respiratory system.

Yet, while the technique has shown promise, its use in patients with ILD in clinical applications is understudied, Denis and colleagues wrote.2 There is limited research comparing ILD and other pulmonary diseases using FOT, and no established cutoffs that could be used to interpret results.

In the new report, Denis and colleagues wanted to see whether FOT could be a reliable tool to predict the progressive course of fibrosing ILD by distinguishing between patients with PPF and stable non-idiopathic pulmonary fibrosis (non-IPF) ILDs.

The authors retrospectively analyzed 160 patients with ILDs who sought care at a single academic medical center. Among those, 94 patients had non-IPF stable ILDs and 45 patients had PPFs. The authors found that those with PPF had lower median resistance at 5 Hz (Xrs5) values during the inspiratory phase (0.31 versus -0.39 cmH2O/[L/sec], P = 0.019595). They also found that Xrs5 had a “moderate” correlation with FVC and DLCO. Lastly, among the entire 160 patients with ILDs, the investigators found Xrs5 correlated with FVC-based disease severity.

“These data show that in a monocentric retrospective cohort of 160 patients with fibrosing ILDs, PFT values correlate moderately with FOT values,” Denis and colleagues wrote.

The investigators wrote that their data show that standard PFTs appear to be superior but pairing those standard tests with Xrs5 could be useful in identifying patients with progressive conditions. The authors noted that they had a limited number of patients with longitudinal data, making it difficult to draw long-term conclusions about the correlation between FOT values and PFT values.

According to Denis and colleagues, the findings are limited by the retrospective, monocentric design of their study. They also cautioned that further research will be needed to more fully understand the potential use of FOT in a clinical setting. Such research should study the reproducibility of FOT values, particularly since some patients with severe pulmonary fibrosis may be unable to perform traditional pulmonary tests. The investigators also noted that their study only includes a single frequency of FOT, underscoring the need for further research.

Nonetheless, the authors concluded that their findings suggest FOT could be a useful tool in the future treatment of patients with PPF.

“The exact contribution of this tool to the diagnosis and follow-up of PPF patients needs to be further determined in a prospective study involving a sufficient number of patients,” they concluded.

References

1. Denis A, Henket M, Giltay L, et al. Forced oscillation technique in progressive pulmonary fibrosis in a single-center retrospective study. Sci Rep. 2025;15(1):15453. Published 2025 May 2. doi:10.1038/s41598-025-99857-1
2. Desiraju K, Agrawal A. Impulse oscillometry: The state-of-art for lung function testing. Lung India. 2016;33(4):410-416. doi:10.4103/0970-2113.184875