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Functional residual capacity and total respiratory system impedance in wheezing infants
K N Desager1, H P Van Bever, M Willemen
1Department of Respiratory Medicine, University Hospital of Antwerp, Belgium.
Insights
Infants with recurrent wheezing may have lung function abnormalities even when symptom-free. Measuring total respiratory system resistance (Rrs) and functional residual capacity (FRC) can detect these issues in a minority of children.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
Background:
- Airway obstruction is evident in infants experiencing acute wheezing.
- Recurrent wheezing episodes in infants may indicate underlying respiratory system dysfunction.
Purpose of the Study:
- To evaluate lung function abnormalities in infants with a history of recurrent wheezing during symptom-free periods.
- To assess total respiratory system resistance (Rrs) and functional residual capacity (FRC) in these infants.
Main Methods:
- Utilized the forced pseudo-random noise (PRN) oscillation technique for Rrs measurements.
- Employed the closed-circuit helium dilution technique for FRC determinations.
- Averaged multiple measurements in 30 infants with recurrent wheezing and 10 healthy controls.
Main Results:
- A reduced functional residual capacity (FRC) was observed in 66% of the infants studied.
- Elevated total respiratory system resistance (Rrs) at 16 Hz was found in 10% of patients.
- Increased specific Rrs (Rrs x FRC) at 16 Hz was detected in 17% of infants.
Conclusions:
- The PRN oscillation technique and helium dilution FRC measurement can identify subtle lung function abnormalities in wheezing infants between acute episodes.
- A minority of infants with recurrent wheezing exhibit measurable lung function deficits during asymptomatic intervals.
Abstract:
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.