OBJECTIVES: I. Compare the resting energy expenditure using respiratory calorimetry in infants and children with moderate to severe cystic fibrosis versus age matched healthy controls.

II. Determine the total energy expenditure and energy spent on physical activity using the doubly labeled water method in these patient populations.

PROTOCOL OUTLINE: Patients and healthy controls receive an oral dose of doubly labeled water following initial urine collection on day 1. Patients undergo additional urine collection at 4-6 hours following doubly labeled water consumption and then daily for 7 days.

Additionally, at the beginning of the study, patients and healthy controls undergo respiratory calorimetry over approximately 45 minutes at rest, starting approximately 2-3 hours after the last meal consumption and last use of aerosol bronchodilators (if required).

PROTOCOL ENTRY CRITERIA:

--Disease Characteristics--

• Diagnosis of cystic fibrosis (CF) by two positive sweat tests No exacerbations of present condition within past 2 months FEV1 less than 50% of predicted No other uncorrected lung disease No requirement for supplemental oxygen

OR

• Healthy (control group) Age matched to CF patients No preexisting lung disease Clinically well No hospitalizations within past 6 months

--Prior/Concurrent Therapy--

• Concurrent pancreatic enzyme supplementation for CF required Clinically stable on current medications (CF patients)

--Patient Characteristics--

• Age: Birth to 12 months 6 to 10 years
• Cardiovascular: No major cardiovascular problems (CF patients) No preexisting heart disease (control group)
• Pulmonary: See Disease Characteristics
• Other: No chromosomal abnormalities (CF patients) No acute infection (CF patients) No diabetes mellitus (both groups)