Chronic instrumentation and its lack of effect on the hemodynamics and regional myocardial blood flow of conscious dogs.

The effects of chronic instrumentation on regional myocardial performance and regional myocardial blood flow were studied in 8 mongrel dogs. Regional segment lengths were measured by an ultrasonic dimension gauge technique at two areas of the left anterior descending coronary artery (LAD) and left circumflex coronary artery (LCX). Regional myocardial blood flow was measured by a tracer microsphere technique. These measurements were repeated while the animals were conscious on the 4th, 11th, 21st and 28th days after instrumentation. On the 4th day, the heart rate was rather high and regional shortening at both the LAD and LCX areas remained suppressed. After the 11th day, hemodynamic variables such as heart rate, left ventricular pressure and regional wall motion were fairly constant. Regional myocardial blood flow and its distribution were also constant throughout the experimental period. Fibrosis of the epicardium invariably induced by surgical procedures did not affect the distribution of regional blood flow as compared with that of the interventricular septum. Thus, a stable hemodynamic state was recorded after the 11th day following surgical manipulation and the implantation of sensors and catheters did not affect the level of regional myocardial blood flow or its distribution at rest. Such long term reproducible measurements of regional wall motion and regional myocardial blood flow may facilitate chronic studies of cardiovascular physiology.