Aim-To assess the eVect of nasal continuous positive airways pressure (CPAP) on the dimensions of the laryngeal opening. Methods-Nine preterm infants who had previously received ventilatory support for respiratory distress syndrome (RDS) were studied. All were receiving nasal CPAP. The laryngeal opening was visualised using a fibre optic video camera system. The ratio of width to length of the opening was measured on and oV CPAP. Results-In eight of the infants the width: length ratio increased on CPAP; mean change for group +24.4% (95% CI +11.9 to +37.9). Conclusions-Nasal CPAP seems to dilate the larynx. This may explain the selective beneficial eVects of CPAP on mixed and obstructive apnoea. (Arch Dis Child Fetal Neonatal Ed 1999;80:F230-F232)
Aim-To measure tidal volume delivery produced by high frequency oscillation (HFO) at a range of frequencies including the resonance frequency. Methods-Eighteen infants with respiratory distress syndrome were recruited (median gestation 28.7 weeks). Each was ventilated at frequencies between 8 and 30 Hertz. Phase analysis was performed at various points of the respiratory cycle. HFO was provided by a variable speed piston device. Resonance frequency was determined from the phase relation between the cyclical movements of the piston and pressure changes at the airway opening. Tidal volume was measured using a jacket plethysmograph. Results-The results were most reproducible when analysis was performed at the end of inspiration (within 1 Hz in nine out of 10 cases). Comparison between tidal volume delivery at 10 Hz and resonance frequency was made in 10 subjects. Delivery was significantly higher at resonance than at 10 Hertz (mean percentage increase 92%, range 9-222%). Conclusions-These preliminary findings suggest that there is improved volume delivery at resonance frequency. (Arch Dis Child Fetal Neonatal Ed 1999;80:F198-F202)
Aim-To observe how the resonance frequency changes with the course of respiratory distress syndrome (RDS), by examining the eVect 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. (Arch Dis Child Fetal Neonatal Ed 2000;83:F203-F206)
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