A Calibration Device to Compare Body Plethysmographs Among Pediatric Lung Function Laboratories

Area of Science:

• Pulmonary Physiology
• Medical Instrumentation

Background:

• Inter-laboratory variability in specific airway resistance measurements using body plethysmography is a significant issue.
• Standardized lung models are needed to ensure consistency in international normative studies.

Purpose of the Study:

• To develop and validate a transportable physical lung analog for assessing body plethysmography equipment.
• To evaluate the accuracy and repeatability of specific airway resistance measurements using the developed analog.

Main Methods:

• A resistor connected to a glass bottle served as the physical analog.
• Thermal time constants were measured with the bottle empty and stuffed with steel wool.
• Gas compression characteristics (isothermal, polytropic, adiabatic) were analyzed at various frequencies.
• The analog's volume and specific resistance were measured in a body plethysmograph.

Main Results:

• The empty analog demonstrated adiabatic gas compression at frequencies ≥0.2 Hz, enabling accurate volume estimation.
• Measurements with the empty analog showed within 5% accuracy and good intersession repeatability.
• The stuffed analog indicated isothermal conditions only at very low frequencies (0.01 Hz).

Conclusions:

• A simple, easily constructed physical analog accurately measures specific airway resistance.
• This apparatus can help standardize and compare body plethysmography equipment across different laboratories.
• The analog facilitates more reliable international normative studies for pulmonary function testing.