Abstract Rationale Post-infectious bronchiolitis obliterans (PIBO) is an obstructive lung disease that develops after severe lower respiratory tract infection. Few studies have assessed quantitative, long-term pulmonary function outcomes in PIBO. This study assesses the quantitative, longitudinal pulmonary function in patients affected by PIBO at a single center with respect to time and inciting respiratory pathogen. Methods Patients were identified from the Research Derivative at Vanderbilt University Medical Center who had developed PIBO, based on physician diagnosis. Pulmonary function test (PFT) results were analyzed using generalized mixed-effects regression to evaluate changes in pulmonary function over time. Restricted cubic splines with four knots were incorporated into the model to account for potential non-linear trends over time. Exploratory analyses were conducted to assess interactions between pathogen and time. Results Fifteen patients were diagnosed with PIBO from 1998-2023. Twelve (80%) were male. Median age of infection was 3 years (yrs). Adenovirus (n = 8/15, 53%) and Mycoplasma pneumoniae (n = 4/15, 27%) were the most identified pathogens. Eleven (n = 11/15, 73%) patients performed PFTs with an initial to final PFT time of 6.4 yrs. (IQR: 3.3 yrs, 8.6 yrs). The initial z-scores of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio were -3.83 (IQR: -4.72, -3.14), -2.92 (IQR: -4.57, -1.61), and -2.61 (IQR: -3.20, -2.08). Final z-scores were -3.82 (IQR: -4.81, -3.16), -1.55 (IQR: -2.12, -1.21), and -3.62 (IQR: -4.30, -3.15). FEV1, FVC, and FEV1/FVC z-scores changed by 0.008/yr (95% confidence interval (CI): 0.029,0.045; p = 0.688), 0.185/yr (CI: 0.061,0.309; p = 0.003), and -0.143/yr (CI: -0.239, -0.046; p = 0.004), respectively (Figure). Six of 9 (67%) patients tested had a positive response to bronchodilators. Patients infected with adenovirus (n = 5/11, 45%) demonstrated greater improvement in FVC than those infected with other pathogens (p 0.001). Conclusion This study shows dysanaptic lung growth in PIBO with greater FVC gain than FEV1, as others have shown; however, this is the first to demonstrate non-linear growth over time. The initial two years after infection seem to be particularly critical as FVC grows most rapidly during this time. This study showed that patients with PIBO may be more bronchodilator responsive than previously thought, as others have also shown. Finally, patients infected with adenovirus demonstrate significant gains in FVC compared with patients infected with other pathogens. Larger, multi-center studies are required to validate these findings, and future research is also needed to explain how severe respiratory infections contribute to non-linear dysanaptic lung growth in susceptible children. This abstract is funded by: N/A
Clegg et al. (Fri,) studied this question.