ABSTRACT
The human diaphragm is relatively inaccessible to direct study. To assess its function, it would be desirable to know the pressure it develops, its position, and its motion. The pressure it develops (transdiaphragmatic pressure, P dJ can be measured relatively noninvasively with gastric and esophageal balloons. Its position and motion, however, generally require measurements that expose the subject to ionizing radiation (radiograms, fluoroscopy, computed tomography) and/or are limited to discrete moments (MRI). Ultrasonography, although it too has distinct limitations, provides an alternative; diaphragm thickness, configuration, and displacement can be evaluated without the use of ionizing radiation, noninvasively, continuously, and with a device that is relatively portable and can be applied to subjects in a variety of postures. This chapter briefly reviews the principles of ultrasonography, some practicalities of using ultrasound for study of the diaphragm, and some current examples of its use in studies of diaphragm function.
