Pressure Transients Occurring in Diastole in the Central Aorta.

• With the development of modern pressure recording systems, and more especially with the advent of currently available catheter tip transducers,* intravascular pressure may now be recorded with an exceedingly high degree of accuracy. Small oscillations in pressure traces that could not previously be clearly distinguished from "catheter-whip" artifact, or that were frequently not seen because of damping in low frequency response systems, take on new meaning and may be studied profitably. Previous authors, using low frequency response systems, have noticed the presence of definite low amplitude positive waves occurring in arterial tracings during diastole." In some instances, e.g., complete heart block, these waves have been shown clearly to be a result of atrial activity. Early workers" have, with painstaking technique, recorded small waves during isometric ventricular contraction. With the use of more modern systems, the recording of central aortic pressure in man, or in the dog, invariably shows a small positive pressure wave immediately preceding the anacrotic limb of the arterial pressure pulse. Although a great many published tracings display such a wave,' no adequate explanation for its presence has been offered. Indeed, textbook illustrations of comparative timing of events in the car-