Radiographic characterization of diaphragmatic excursion in halothane-anesthetized ponies: spontaneous and controlled ventilation systems

A radiograph technique for identification of diaphragmatic segments and quantitation of their contribution to total diaphragmatic function was developed. Five anesthetized ponies were studied on 3 separate occasions. Studies were made of the ponies in left lateral recumbency at 2 anesthetic levels (1 and 2 minimal alveolar anesthetic concentrations; halothane) and under spontaneous and controlled ventilation systems. General pattern of diaphragmatic displacement was unchanged by increased depth of anesthesia. Controlled ventilation altered the pattern of diaphragmatic displacement. Diaphragmatic displacement and regional volume changes were a function of active contraction or passive movement.