Resonance frequency in respiratory distress syndrome.

AIM To observe how the resonance frequency changes with the course of respiratory distress syndrome (RDS), by examining the effect of changing static compliance on the resonance frequency in premature infants. METHODS In 12 ventilated premature infants with RDS (mean gestational age 26.6 weeks, mean birth weight 0.84 kg), resonance frequency and static compliance were determined serially using phase analysis and single breath mechanics technique respectively in the first seven days of life. RESULTS The minimum number of measurements done in any one baby was three and maximum was five in this seven day study period. The first measurement in each baby was done within the first 72 hours of life. The increase in compliance in this period varied from 27% to 179%. The variation in the corresponding resonance frequency was within 2 Hz in eight babies and within 6 Hz in all recruited babies. CONCLUSIONS The resonance frequency of the respiratory system in preterm infants with RDS remains remarkably constant in the early stages of the illness, despite relatively large changes in static compliance.