A radiographic method for estimating lung volumes in sick infants

Area of Science:

• Pediatric Pulmonology
• Medical Imaging
• Respiratory Physiology

Background:

• Accurate estimation of lung volumes in infants, especially those with bronchopulmonary dysplasia (BPD), is challenging with conventional methods.
• Existing techniques for measuring thoracic gas volume (TGV) and functional residual capacity (FRC) in infants are often complex and debated.

Purpose of the Study:

• To compare thoracic gas volume (TGV) and functional residual capacity (FRC) measurements with planimetric analysis of chest radiographs.
• To evaluate the reliability of planimetry for estimating lung volumes in infants diagnosed with bronchopulmonary dysplasia (BPD).

Main Methods:

• Twenty-six infants with BPD underwent measurements of TGV (using infant whole body plethysmography) and FRC (using nitrogen washout).
• Planimetric measurements of lung areas from anteroposterior chest radiographs were obtained.
• Tidal volume (TV) was added to TGV and FRC to account for differences in measurement timing (end-expiration vs. end-inspiration).

Main Results:

• Regression equations were derived: [TGV+TV](mL) = 3.3 mL/cm² x [A+B] cm² + 24 mL and [FRC+TV](mL) = 3.5 mL/cm² x [A+B] cm² - 13.5 mL.
• A strong correlation (r=0.9) was observed between TGV and lung areas measured by planimetry.
• A moderate correlation (r=0.7) was found between FRC and lung areas, indicating TGV's stronger association.

Conclusions:

• Planimetric measurement of lung areas on chest radiographs correlates closely with physiological lung volume measurements (TGV and FRC).
• The planimetric method provides an inexpensive and reliable approach for estimating lung volumes in infants with BPD.
• Chest radiography planimetry is a valuable tool for assessing lung volumes when available for infants suffering from BPD.