Progressive decline in plethysmographic lung volumes in infants: physiology or technology?
During the last 30 years, there has been an unexplained trend toward declining values for plethysmographic assessments of lung volume at functional residual capacity (FRC) in infants. The aim of this study was to compare data collected from healthy infants using contemporary equipment with published reference data and to explore reasons for discrepancies. Lung volumes were measured in 32 healthy infants (age, 4-93 weeks; weight, 3.9-12.4 kg) using a new, commercially available infant plethysmograph. Mean (SD) FRC was 19.6 (3.4) ml/kg (within subject coefficient of variation 3.4 [2.3%]), which was on average 7.0 [3.5] ml/kg and 2.3 [1.2] SD (Z) scores lower than the recently collated reference data from an American Thoracic Society task force. A total of 66% of these healthy infants had a FRC that was below the predicted normal range. Comparison of equipment, software, and protocols with those from previous reports revealed the importance of minimization of dead space and of adequate subtraction of all compressible occluded volume when calculating FRC in infants. These findings emphasize the need to establish reference data for lung function tests in infants that are appropriate for the equipment and protocols in current use.
Hülskamp
Georg
G
Portex Anaesthesia, Intensive Therapy and Respiratory Medicine Unit, Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust, London, UK. g.hulskamp@ich.ucl.ac.uk
Hoo
Ah-fong
AF
Ljungberg
Henrik
H
Lum
Sooky
S
Pillow
J Jane
JJ
Stocks
Janet
J
D000367:Age Factors; D001724:Birth Weight; D001827:Body Height; D001835:Body Weight; D002985:Clinical Protocols / Q000592:standards; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D005260:Female; D005652:Functional Residual Capacity; D005865:Gestational Age; D006801:Humans; D007223:Infant; D008176:Lung Volume Measurements / Q000295:instrumentation / Q000379:methods*; D008297:Male; D010993:Plethysmography, Whole Body / Q000295:instrumentation / Q000379:methods* / Q000639:trends*; D011237:Predictive Value of Tests; D012016:Reference Values; D012126:Respiratory Dead Space; D012984:Software / Q000592:standards