MEASUREMENTS OF INTRAMYOCARDIAL PRESSURE

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Abstract
Pressure pulses registered from myocardial pockets of fluid by means of vessel segments imbedded in the myocardium of the left ventricle generally exceed by considerable amounts the aortic pressure simultaneously recorded. However, such pressures are in part artefacts and hence do not crucially demonstrate that intramyocardial pressure exceeds left ventricular pressure during systole. The following evidence supports this view: The pressure pulse from an intramyocardial pocket of fluid increases progressively to values greater than aortic pressure upon raising the diastolic pressure in the pocket of fluid, and hence it is probably a function of the degree of localized muscle stretch induced by the applied internal pressure. When blood from the aorta flows through an imbedded segment a systolic flow may occur. Pressures recorded from closed vessel segments in the left ventricular wall or cavity may have two to four times the ordinate value of the intraventricular pressure, although the usual values are somewhat lower. Protection of the segment in the cavity or wall by a loose fitting fenestrated cap or retractable metal sleeve reduces the recorded pressure pulse in the left ventricular cavity, in many experiments, to values approximating aortic pressure, and in the myocardium to values somewhat less than aortic pressure. Theoretical and exptl. evidence is given to show that pressure transfer through protected vessel segments is generally not complete. Pressure transfer exceeds 100% when there is movement and distortion of the segment as a result of turbulent flow or mechanical impact. Although the use of the vessel segments may give directional changes, exact quantitation of intramyocardial pressure is not yet believed a reality.