Local Dimensional Changes of the Myocardium Measured by Ultrasonic Technique

Pairs of ultrasonic elements (piezo-electric ceramics of lead zirconate titanate) were implanted in the myocardium with 0.8–1.2 cm between the elements. Measurements of mural thickness or distance variations along the muscle layers, myocardial chord length (MCL), were performed in anesthetized and conscious dogs. Mural thickness varied reciprocally to MCL during the heart cycle, both with amplitudes of 8—15 per cent of end-diastolic lengths. Shortening usually started in the apical and interventricular parts, whereas shortening of the myocardium close to the base was often delayed. This asynchrony may reflect differences in end-diastolic myocardial fibre lengths. During the isovolumic phase, dimensional changes were small or absent. Comparative measurements with mercury-in-rubber gauges revealed that the considerable isovolumic expansion produced by this technique was an artefact due to stretching of the muscle fibres by the gauges.