Infant spirometry as a predictor of lung function at early childhood in cystic fibrosis patients

BACKGROUND: Infant pulmonary function testing using the raised volume rapid thoracoabdominal compression (RVRTC) technique requires sedation and is time consuming. Many cystic fibrosis (CF) centers do not have access to equipment and the utility of routine testing remains to be determined. We aimed to assess whether RVRTC tests performed during infancy predict spirometry at early school age. METHODS: The RVRTC-based forced expiratory flow measures in infants were compared to the first adequately performed spirometry at school age. All tests were carried out during routine clinic visits and expressed as age related z-scores; only test occasions where patients were considered stable were included in the analysis. RESULTS: 47 patients had useable infant RVRTC as well as matching school age spirometry data. There was weak correlation between infant FEV_0.5 and early school age FEV₁ (R = 0.29, p = 0.05). Four infants had significantly low zFEV_0.5 (zFEV_0.5 < -1.96), of which one of those remained under that limit at childhood. Changes in spirometry between infancy and early childhood were negatively correlated to baseline FEV_0.5 (R = 0.61 p<0.001) reflecting that the change was driven by where individuals started off with. There was no difference in clinical characteristics between those improving, those with stable or deteriorating in lung function. CONCLUSION: Infant RVRTC measures were not predictive of pulmonary function in early school age, likely due to the high proportion of measures of forced expiratory flows within the normal range at both time points.