Measurement of cardiac pressure-length loops using an improved sonomicrometer. Accuracy and effect of respiration.
A transit-time sono-micrometer for measurement of myocardial dimensions is described. Crystals of frequencies 1-10 MHz can be used, enabling a large range of distances to be measured. The meter has two channels, operated in sequence to avoid interference between channels. By combining local muscle segment length with the left ventricular pressure in open-chest cats, the pressure-length loop for that segment was continuously displayed. A calibration procedure was developed, permitting calibration to be registered on a recorder and on a storage monitor at any time. Detailed interpretation of loops from normal and ischaemic segments of the left ventricle is presented. Variation of the loop form with respiration is demonstrated, which clearly necessitates a standardized reference point in the respiratory phase for comparing loops from two or more experimental situations.
D000818:Animals; D002415:Cats; D006321:Heart / Q000033:anatomy & histology* / Q000502:physiology; D011312:Pressure; D012119:Respiration; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation*