Coronary Circulation in the Conscious Dog with Cardiac Neural Ablation

The left coronary circulation at rest and during its response to natural stresses was studied in five conscious dogs whose hearts had been externally denervated (stripping technique). The values were compared to those obtained under similar conditions in normal dogs of comparable weight and training. A high degree of hyperemia after temporary circumflex occlusion and a coronary flow pattern with a dominant diastolic component under the different conditions were similar to that of the normal dog. At rest, circumflex flow and myocardial oxygen use were only about half the values obtained in the normal dog. In moderate exercise, the rise of circumflex flow was delayed 10-30 seconds, being always preceded by an elevation of stroke volume. In excitement, the increase in circumflex flow was delayed 7-12 seconds, and this was also generally preceded by a rise in stroke volume. The large rise of coronary flow in exercise was associated with a marked increase in myocardial blood oxygen extraction; in excitement, coronary flow also rose greatly but oxygen extraction decreased markedly. Although these trends during natural stress states were similar to those found in the normal dog, the maximum coronary flow and myocardial oxygen use were no more than half those found in the normal dog for an equivalent stress. The addition of beta-receptor blockade still further reduced the coronary responses to these natural stresses. Thus the denervated heart appears to function at a lower metabolic level than the heart with intact cardiac nerves.