Pulmonary Diffusing Capacity in Normal Children, Ages 4 to 13: The Effect of Body Position and Exercise on Pulmonary Diffusing Capacity, Lung Volumes, and Ventilatory Tests

CARBON MONOXIDE absorption, the pulmonary diffusing capacity (D_l), and the pulmonary capillary blood volume (V_c) are less in normal adults in the upright than in the supine position.^1,2 The ventilation-perfusion relationship of the normal adult lung is different in the upright and the supine position, and the upper regions of the lung are poorly perfused in the upright position. These differences have been related to the existence in the upright position of a pressure gradient and a capillary bedfilling gradient which are dependent upon gravity.³ Exercise in the adult results in increases in D_l and V_c which are greater in magnitude than those found in changing from the upright to the supine position.⁴ Very few D_l and V_c measurements have been reported in children under the age of 13,⁵ and the physiological relationships of D_l and V_c to