Introduction: A simple, accurate technique to measure Total Lung Capacity (TLC) in neonates to follow the progression of respiratory disease and the response to therapy would be helpful. Therapy with mechanical ventilation, cannot assess lung volumes. Objective: Using a rabbit model, we adapted a semi-automated technique, to estimate TLC from a PA and lateral CXR. The lung volume of rabbits closely mimics lung volumes of human neonates. Methods: The TLC of 14 rabbits, weighing between 2.24 and 3.0 kg. was calculated using Barnhard's five ellipsoid thoracic model (Am J Med 1960:28; 51-60). PA & lateral images were obtained by Fuji Computed Radiography. Lung regions were located by divide and search algorithm. Upon sacrifice, the clamped end inspiratory lungs were excised, and volume measured by volumetric H2O displacement. Results: TLC measured by computer was correlated with actual lung volume (r=0.787) see fig. with 95% CI. Conclusion: This new computerized technique of measuring TLC in a model with small lungs, such as the rabbit, is accurate and thus may be applicable to neonates.

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