REGIONAL FIBER STRESS FIBER STRAIN AREA AS AN ESTIMATE OF REGIONAL BLOOD-FLOW AND OXYGEN-DEMAND IN THE CANINE HEART

1. In the present study the relation between regional left ventricular contractile work, regional myocardial blood flow and oxygen uptake wa s assessed during asynchronous electrical activation. 2. In analogy to the use of the pressure-volume area for the estimation of global oxyg en demand, the fibre stress-fibre strain area, as assessed regionally, was used to estimate regional oxygen demand. The more often used rela tion between the pressure-sarcomere length area and regional oxygen de mand was also assessed. 3. Experiments were performed in six anaesthet ized dogs with open chests. Regional differences in mechanical work we re generated by asynchronous electrical activation of the myocardial w all. The ventricles were paced from the right atrium, the left ventric ular free wall, the left ventricular apex or the right ventricular out flow tract. Regional fibre strain was measured at the epicardial anter ior left ventricular free wall with a two-dimensional video technique. 4. Regional fibre stress was estimated from left ventricular pressure , the ratio of left ventricular cavity volume to mall volume, and regi onal deformation. Total mechanical power (TMP) was calculated from the fibre stress-fibre strain area (SSB) and the duration of the cardiac cycle (t(cycle)) using the equation: TMP = SSA/t(cycle). Regional myoc ardial blood flow was measured with radioactive microspheres. Regional oxygen uptake was estimated from regional myocardial blood flow value s and arteriovenous differences in oxygen content. 5. During asynchron ous electrical activation, total mechanical power, pressure-sarcomere length area, myocardial blood flow and oxygen uptake were significantl y lower in early than in late activated regions (P < 0.05). 6. Within the experiments, the correlation between the pressure-sarcomere length area and regional oxygen uptake was not significantly lower than the one between total mechanical power (TMP) and regional oxygen uptake (V -O2.reg). However, variability of this relation between the experiment s was less for total mechanical power. Pooling all experimental data r evealed: V-O2.reg = k(1) TMP + k(2), with k(1) = 4.94 +/- 0.31 mol J(- 1) and k(2) = 24.2 +/- 1.9 mmol m(-3) s(-1) (means +/- standard error of the estimate). 7. This relation is in quantitative agreement with p reviously reported relations between the pressure-volume area and glob al oxygen demand. The results indicate that asynchronous electrical ac tivation causes a redistribution of mechanical work and oxygen demand and that regional total mechanical power is a better and more general estimate of regional oxygen demand than the regional pressure-sarcomer e length area.