Functional residual capacity and total respiratory system impedance in wheezing infants

Pediatr Pulmonol. 1994 Jun;17(6):354-8. doi: 10.1002/ppul.1950170603.


Airways obstruction has been demonstrated in acutely wheezing infants. The aim of the present study was to assess functional abnormalities as detected by measurement of total respiratory system resistance (Rrs) and functional residual capacity (FRC) in infants with a history of recurrent episodes of wheezing, while not acutely ill. In 30 such infants (mean age, 10 months; range, 4-17) and in 10 healthy infants (mean age, 6 months; range, 0-14) four Rrs measurements, performed with the forced pseudo-random noise (PRN) oscillation technique, and three FRC determinations, using the closed-circuit helium dilution technique, were averaged. A lower than predicted FRC was demonstrated in 20/30 (66%) patients. At 16 Hz, Rrs was significantly above predicted in 3/30 (10%) patients. Specific Rrs (Rrs x FRC) at 16 Hz was increased in 5/30 (17%) patients. In conclusion, the PRN oscillation technique combined with FRC measurement by helium dilution detects lung function abnormalities in a minority of wheezing infants during symptom-free intervals.

MeSH terms

  • Airway Resistance / physiology*
  • Case-Control Studies
  • Chloral Hydrate
  • Functional Residual Capacity / physiology*
  • Helium
  • Humans
  • Infant
  • Infant, Newborn
  • Lung / physiology*
  • Lung / physiopathology
  • Oscillometry
  • Peak Expiratory Flow Rate
  • Plethysmography, Whole Body
  • Pulmonary Ventilation
  • Regression Analysis
  • Reproducibility of Results
  • Respiratory Sounds
  • Spirometry
  • Tidal Volume / physiology*


  • Helium
  • Chloral Hydrate