During the past 18 months more than 100 normal and abnormal subjects have been studied with this instrument in our laboratory, utilizing the recorded heart sounds, the carotid sphygmogram or the electrocardiogram as the primary points of time reference. We have been impressed with the inconstancy in the timing of the electrokymographic events obtained in ventricular tracings when studied with any of the above methods. The objections to each of these timing devices are well known. Thus, the factors of variability in the carotid sphygmogram which may be consequent upon variation of the rate of blood flow, elasticity and distensibility of the vessel have been discussed.' The validity of a comparison of the mechanical events in the cardiac cycle with the electrocardiogram has been called into question.7 The heart sounds represent a fusion of noises arising from both ventricles and are

This communication describes and discusses the results obtained in studying central and )eripheral arterial pressure pulses in man by means of retrograde aortic catheterization. The pressure pulse transformation and pulse transmission in the aorticobrachial system are presented and compared with comparable tracings reported in the dog. Several normal subjects and patients with hypertension, aortic regurgitation and coarctation of the aorta were studied. The genesis of the central pulse contour in aortic regurgitation is reconsidered. The changes in central pulse pressure, produced by the Valsalva-like maneuver, and ventricular premature systoles have been investigated, especially in their relationship to cycle length, end-diastolic volume and peripheral resistance. The technic of obtaining pulse pressure recordings by retrograde aortic catheterization is recommended for determining the location, size and dynamic significance of coarctation of the aorta. As an additional study, aortic densograms and border electrokymograms from the aortic arch and left ventricular border were correlated with simultaneously recorded central aortic pressure tracings.C ATHETERIZATION of the human aorta has been used recently for diagnostic purposes in retrograde angiocardiography." 2 This experience prompted the study of cardiovascular hemodynamics by means of retrograde catheterization of the human aorta, a field which has been little explored. This report deals with some preliminary observations on the contour, transmission rate and transformation of the central aortic pressure pulse. As part of this investigation the central pressure pulse was correlated with the simultaneously recorded electrokymogram of the aorta. METHODS AND PROCEDURESimultaneous aortic catheterization and electrokymography were performed in patients for whom the information so gained was thought to be diag-

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