Conference Coverage

Tracheobronchial tree size changes may predict IPF outcomes

Dr. Vera De Palo

Vera De Palo, MD, FCCP, comments: The findings of the work by Dr. Ratwani and his collaborators are intriguing. It is attractive to have a noninvasive measurement, like tracheobronical tree change, that could correlate with prognosis in IPF. It is interesting that the researchers did not see a correlation between tracheal size and lung volume. Continued study may provide more insight to help inform stage, prognosis, and possibly to help guide potential therapies for our patients with IPF.



Changes in tracheobronchial tree size may serve as a practical and noninvasive method for predicting disease severity in patients diagnosed with idiopathic pulmonary fibrosis, according to data from 150 adults.

To determine the potential predictive value of tracheobronchial tree changes on mortality, Ankush Ratwani, MD, of Georgetown University, Washington, and colleagues reviewed data from adults with IPF seen at a single center between March 2012 and December 2016. The findings were presented at the CHEST annual meeting.

The researchers measured the tracheal diameters of the patients and used the GAP index, an established system for predicting mortality in IPF patients, to determine a relationship. Overall, they found a significant correlation between GAP index scores and increasing tracheobronchial tree size across eight measurements of different levels along the tracheobronchial tree “with an increase in GAP index stage for every level of increase in tracheal measurements (P less than .005),” they noted.

Measurements included the anterior-posterior diameter at the subglottic level, aortic arch, carina, right main stem bronchus, and left main stem bronchus, as well as transverse diameter assessment at the subglottis, aortic arch, and carina. The average anterior-posterior tracheal diameters were 21.77 mm for the subglottis, 21.84 mm for the aortic arch, 20.47 mm for the carina, 15.19 for the right main stem bronchus, and 14.21 mm for the left main stem bronchus.

No correlation appeared between tracheal size and lung volume, which suggests that enlargement of the trachea is likely caused by other factors beyond fibrosis, and next steps for research should determine whether tracheal size is an independent predictor of mortality in IPF patients, the investigators noted.

“With the field of treatment and management changing for IPF over the last few years, it has becoming increasingly important to prognose these patients in order to find where they fit in the spectrum for treatment or lung transplant,” Dr. Ratwani said in an interview. “Additionally, there needs to be a noninvasive measure to show disease progression, such as with using CT scans, and correlate with other prognostic indicators to hopefully create a regression formula that encompasses multiple parameters,” he explained.

“The results were surprising in that there was a correlation of a radiographic measure that has not been looked at previously with a validated measure of prognostication in IPF (GAP Index),” Dr. Ratwani said.

Although the findings do not imply more than a correlation, the results serve as “a good start to validate the theory that as the distal airways enlarge (traction bronchiectasis) in later stages of IPF, so may the proximal airways, which may be used to easily measure disease progression and guide the conversation for transplant or treatment,” Dr. Ratwani noted. His next steps for research include studying transplant-free survival in correlation with tracheal size, as well as serial changes between CT scans with correlations of lung volumes and survival.

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