A model of transient myocardial dysfunction in conscious dogs. Regional shortening in the presence of impaired coronary flow reserve and treadmill exercise.

An experimental model of treadmill exercise-induced regional myocardial dysfunction was developed in conscious dogs to mimic exertional angina pectoris in man. Twenty mongrel dogs, trained to run on a treadmill, were chronically instrumented with a miniature pressure transducer in the left ventricle and a hydraulic occluder placed around the circumflex branch of the left coronary artery. Two pairs of piezoelectric crystals for sonomicrometry were implanted subendocardially to measure regional myocardial function. Experiments were started 1 week after surgery. In the first group of ten dogs exercise with constant work load of 10 km/hr and 10% elevation during partial left coronary artery stenosis, induced by external filling of the occluder, produced comparable episodes of regional dysfunction in the left coronary artery area during five subsequent treadmill runs and recovery of function after each run. The second group of ten dogs, exercised with left coronary artery stenosis and increasing working load, exhibited minimal regional dysfunction in the left coronary artery area while running at 6 km/hr and 6% elevation, but maximal regional dysfunction during peak exercise (10 km/hr and 10% elevation). This load dependency and recovery of function after the runs was demonstrated during five identical consecutive exercise cycles. This model, in contrast to those using ameroid constrictors, enables various drugs to be tested in a single instrumented dog over a period of several weeks.