The overall objective of this study is to determine the impact early nutritional and respiratory indices have on early CF lung disease. This knowledge will guide clinical management of infants with CF, who are now primarily diagnosed through newborn screening.

The overall objective of this study is to determine the impact early nutritional and respiratory indices have on early CF lung disease. This knowledge will guide clinical management of infants with CF, who are now primarily diagnosed through newborn screening. We hypothesize that respiratory and nutritional indices during the first year of life are critical determinants of lung function in infants and preschoolers with CF.

Aim #1 - To examine the relationship between nutritional status (weight-for-age (WFA) and weight-for-length (WFL)) at 6 months of age and lung function at 1-2 years of age in infants with CF.

Hypothesis: Infants with CF with poor nutritional status at 6 months of age will have worse lung function, as assessed through the raised volume rapid thoracoabdominal compression technique and plethysmography, compared to those with better nutritional indices, defined as improved weight-for-age and weight-for-length.

Aim #2 - To examine the relationship between nutritional status (WFA and WFL) in infants with CF at 12 months of age and the lung clearance index (LCI) at 3-5 years of age.

Hypothesis: Infants with CF with poor nutritional indices at 12 months of age will have a higher (worse) LCI at 3-5 years of age compared to those with better nutritional status.

Aim #3 - To delineate the relationship between passive tidal breathing lung function testing in infants with CF at 4-8 weeks of age and subsequent lung function at 6-12 months of age.

Hypothesis: Abnormalities in passive tidal breathing lung function testing will be associated with abnormal infant pulmonary function testing obtained via the raised volume rapid thoracoabdominal compression technique and plethysmography at 6-12 months of age.

Inclusion Criteria:

• Informed consent by a parent or legal guardian
• A confirmed diagnosis of CF by newborn screening and either a documented sweat chloride of at least 60 mEq/L by quantitative pilocarpine iontophoresis or a genotype with two CF-causing mutations
• One month to five years of age.

Exclusion Criteria:

• Chronic lung disease not due to CF
• Contraindications to sedation, including structural abnormalities of the upper airway or chest wall and severe gastroesophageal reflux
• Gestational age < 36 weeks

Infants and preschoolers with cystic fibrosis diagnosed by newborn screen.