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It has been demonstrated by Henny, Boone, Chamberlain, and their associates that border movements of the heart and great vessels may be recorded with the electrokymograph (1, 2, 4, 7). Confirmation of this work has been reported by others (3. 5, 6). Our studies were designed to investigate the accuracy with which movements of the aorta and pulmonary artery could be recorded with this instrument, and the significance of these movements as measures of dynamic cardiovascular changes during certain acute disturbances of the circulation. For these experiments, acute intrathoracic pressure variation was chosen as the implement for the production of circulatory disturbances. It is a procedure with which a new investigative method may be evaluated by comparison with observations of venous, arterial and pulmonary arterial blood pressure. cardiac output, roentgenokymographv, and roentgenographic lung density in control studies or in the published reports of others. The electrokymograph utilizes the roentgen ray beam of the fluoroscope. When the long axis of a small rectangle of fluoroscopic screen is placed perpendicular to the pulsating border of the heart or a great vessel, the average intensity of illumination of the whole rectangle will vary with the motion of the border. When movements of a great vessel are recorded, the dense shadow moves outward in systole to diminish the intensity and in diastole the reverse occurs. These changes in illumination, when viewed by a sensitive photoelectric tube, are converted to electrical impulses which are recorded by an electrocardiographic apparatus.

THE VALIDITY OF THE ELECTROKYMOGRAPHIC METHOD FOR MEASUREMENT OF DIAMETER CHANGE OF THE AORTA AND PULMONARY ARTERY DURING CIRCULATORY DISTURBANCE1