REGIONAL VASCULAR RESERVE IN CANINE ATRIA AND VENTRICLES DURING REST AND EXERCISE

Vascular reserve, which defines the capacity for further vasodilation in a given physiological or pathological condition, has not been measu red in the canine atria. This study defines, in normal dogs, the regio nal vascular reserve simultaneously measured in the atria (appendage, nonappendage regions) and in the ventricles during rest and two levels of exercise. Blood flow was determined using 11.4 +/- 0.1 mu m radiol abeled microspheres. Vascular reserve (percent for each region) is the ratio of vascular conductance during each condition to maximum vascul ar conductance. Maximum vascular conductance was estimated by infusing adenosine intravenously. For a given physiological condition regional vascular conductance varied two- to threefold. The vascular reserve o f each of the regions decreased progressively from rest to mild exerci se to moderate exercise. Regional vascular reserve for both atria, the right ventricle, and the epicardial layer of the left ventricle was e ssentially uniform for a given condition: rest 93 +/- 0.4%, mild exerc ise 81 +/- 1.2%, and moderate exercise 69 +/- 1.5%. This similarity in vascular reserve implies that for a given physiological condition a c ommon mechanism precisely regulates myocardial perfusion in these card iac regions as a function of the total vasodilator capacity.