SPATIAL HETEROGENEITY OF BLOOD-FLOW IN THE DOG HEART .2. TEMPORAL STABILITY IN RESPONSE TO ADRENERGIC-STIMULATION

The effects of adrenergic stimulation on local myocardial blood flow i n the left ventricle were studied in 13 anaesthetized Beagle dogs usin g the tracer microsphere technique. Adrenergic stimulation was induced by intravenous infusion of orciprenaline (1-2 mu g kg(-1) min(-1)) ov er 15 min or by electrical stimulation of the left ansa subclavia (10 Hz, 1 ms, 4-8 V) over 5 min. Local myocardial blood flow was analysed in 256 samples with an average (+/-SD) mass of 318+/-49 mg from the le ft ventricular myocardium using a standardized dissection procedure. O rciprenaline increased the average myocardial blood flow from 0.85+/-0 .18 to 1.73+/-0.27 mi min(-1) g(-1) while oxygen consumption and the p ressure-rate product increased by 129 and 119% respectively. The coeff icients of variation of local myocardial blood flow, a measure of spat ial blood flow heterogeneity, were 0.21 and 0.18 under control and orc iprenaline respectively. Except for a slight transmural gradient (endo myocardium/epimyocardium flow ratio 1.19) myocardial blood flow did no t exhibit significant spatial gradients. Stimulation with orciprenalin e increased the average blood flow in all regions of the left ventricl e by comparable extents. However, local blood flow during orciprenalin e was significantly lower in samples from regions which had a lower bl ood flow under resting control conditions. A significant positive rela tionship was obtained between local myocardial blood flow under restin g conditions and orciprenaline (r=0.45+/-0.18). Moreover, after recove ry from orciprenaline stimulation (i.e. 40-112 min after the end of or ciprenaline infusion) local myocardial blood flow exhibited a high deg ree of correlation with local flow before orciprenaline (r=0.71+/-0.08 ). Comparable results were obtained with electrical stimulation of the left ansa subclavia. For the comparison stimulation vs. control, the correlation coefficient of local blood flow was 0.52+/-0.04 and for re covery vs. control 0.77+/-0.06. From these results it is concluded fir stly that local myocardial blood flow under resting conditions is an i mportant determinant of local flow during adrenergic stimulation. Seco ndly, the anatomical region does not have any predictive value for the blood flow change during adrenergic stimulation and finally, the clos e relationship between local blood flow before and after cardiac stimu lation indicates that the spatial blood flow heterogeneity is temporal ly stable over hours.