Respiratory rate in infants with cystic fibrosis throughout the first year of life and association with lung clearance index measured shortly after birth

Background: Lung impairment in cystic fibrosis (CF) starts in infancy. However, tools to monitor early lung disease are limited. Respiratory rate (RR) as a key vital sign is easy to assess during sleep and is elevated during acute respiratory disease. Thus, elevated RR could indicate early lung impairment and potentially serve as a diagnostic tool in disease monitoring. Methods: In a prospective cohort of infants with CF diagnosed by newborn screening and healthy controls RR was measured and respiratory symptoms reported weekly throughout infancy. Infants performed a lung function measurement within the first weeks of life. Results: The analyses included 5656 measurements from 153 infants (43 with CF). RR declined from 43.2 (40.5)/min at 6 weeks of age to 28.3 (24.6)/min at 50 weeks in infants with CF (healthy controls). Infants with CF had consistently higher RR than controls (mean difference: 4.15/min; (95% CI 2.86-5.44); p <.001). In both study groups, RR was increased throughout the study period in infants with higher lung clearance indices (LCI) and during episodes of respiratory infections. Conclusions: Infants with CF have a higher RR compared to healthy controls during the first year of life. The association with early LCI measurements, the current gold standard to assess physiology of peripheral airways persisted throughout the study period. This may indicate tracking of lung function by RR. It might thus be an early subtle sign of functional respiratory deficit. Further studies will show if RR can be used as a sensitive and promising marker to monitor early CF lung disease. (C) 2018 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.