Cardiac size in the supine chestfilm.

The aim of this study was to find a normal value for the cardiac size in the supine position because such a standard is hardly known in the literature. Cardiac size in the erect and supine positions were compared in 165 patients in whom both chest radiographs were performed prior to kidney transplantation. For cardiac size as well as for cardiothoracic ratio (CTR) there is a linear relation between the measured values in the two positions which allows to determine the cardiac size in the supine position from a radiograph taken in the erect position and thus to determine whether cardiac enlargement exists in a supine chest film. A survey of 100 patients without cardiac or pulmonary pathology showed 16 patients with a heart size over 15 cm, the upper limit of normal as established over 20 years ago, which suggests that nowadays a new standard might be set. If so, the upper limit of normal CTR is 0.55 in the erect and 0.58 in the supine position. Two figures are presented to determine cardiac size and CTR in the supine position from the measured values in the erect position and vice versa.