Progressive Decline in Plethysmographic Lung Volumes in Infants: Physiology or Technology?

• Published in: American journal of respiratory and critical care medicine Vol. 168; no. 8; pp. 1003 - 1009
• Main Authors: Hulskamp, Georg, Hoo, Ah-fong, Ljungberg, Henrik, Lum, Sooky, Pillow, J. Jane, Stocks, Janet
• Format: Journal Article
• Language: English
• Published: New York, NY Am Thoracic Soc 15.10.2003; American Lung Association
• Subjects: Age Factors; Air breathing; Biological and medical sciences; Birth Weight; Body Height; Body Weight; Clinical Protocols - standards; Cohort Studies; Data Interpretation, Statistical; Female; Functional Residual Capacity; Fundamental and applied biological sciences. Psychology; Gestational Age; Humans; Infant; Lung Volume Measurements - instrumentation; Lung Volume Measurements - methods; Male; Plethysmography, Whole Body - instrumentation; Plethysmography, Whole Body - methods; Plethysmography, Whole Body - trends; Predictive Value of Tests; Reference Values; Respiratory Dead Space; Respiratory system: anatomy, metabolism, gas exchange, ventilatory mechanics, respiratory hemodynamics; Software - standards; Vertebrates: respiratory system; Human; Lung volume; Lung function; respiratory function tests; Infant; Physiology; Plethysmography; functional residual capacity
• ISSN: 1073-449X; 1535-4970
• DOI: 10.1164/rccm.200303-460OC

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.