Normal Growth and Physiology

Abstract

In analyzing a chest radiograph, it is important to have an understanding of some of the basic principles of respiratory physiology, and to appreciate how certain pathophysiological processes can cause distinct disease states, each with its own specific clinical signs and symptoms. These can be divided into broad categories, which include obstructive lung disorders, restrictive lung disorders, disorders of gas diffusion, shunts, and ventilation-perfusion abnormalities. For the pediatric radiologist, lung mechanics and in particular those related to changes in lung volume are of crucial significance. The radiograph of the noncooperative young child is never obtained at the optimal full inflation typical for the older person who inhales to full lung capacity (thus, total lung capacity) and breath-holds. The lung volumes reflected in the pediatric radiograph (assuming quiet breathing) span a volume range from FRC (the volume at end expiration) to peak of tidal volume (the volume at end inspiration). Thus, by definition, the volume of the normal pediatric radiograph is always well below the lung volume of the cooperative patient, with all the implications that this has on the quality of the radiograph. Obviously, the lower the lung volume, the less reliable is the interpretation of pathology.