Pattern differences between distributions of microregional myocardial flows in crystalloid- and blood-perfused rat hearts

Abstract

hiko Kajiya. Pattern differences between distributions of microregional myocardial flows in crystalloid-and blood-perfused rat hearts. Am J Physiol Heart Circ Physiol 286: H1331-H1338, 2004. First published December 11, 2003 10.1152/ajpheart.00120.2003.-Regional myocardial flow distributions in Langendorff rat hearts under Tyrode and blood perfusion were assessed by tracer digital radiography (100-m resolution). Flow distributions during baseline and maximal hyperemia following a 60-s flow cessation were evaluated by the coefficient of variation of regional flows (CV; related to global flow heterogeneity) and the correlation between adjacent regional flows (CA; inversely related to local flow randomness). These values were obtained for the original images (64 2 pixels) and for coarsegrained images (32 2 , 16 2 , and 8 2 blocks of nearby pixels). At a given point in time during baseline, both CV and CA were higher in blood (n ϭ 7) than in Tyrode perfusion (n ϭ 7) over all pixel aggregates (P Ͻ 0.05, two-way ANOVA). During the maximal hyperemia, CV and CA were still significantly higher in blood (n ϭ 7) than in Tyrode perfusion (n ϭ 7); however, these values decreased substantially in blood perfusion and the CV and CA differences became smaller than those at baseline accordingly. During basal blood perfusion, the 60-s average flow distribution (n ϭ 7) showed a smaller CV and CA than those at a given point in time (P Ͻ 0.05, two-way ANOVA). Coronary flow reserve was significantly higher in blood than in Tyrode perfusion. In conclusion, the flow heterogeneity and the local flow similarity are both higher in blood than in Tyrode perfusion, probably due to the different degree of coronary tone preservation and the presence or absence of blood corpuscles. Under blood perfusion, temporal flow fluctuations over 60-s order are largely involved in shaping microregional flow distributions. regional myocardial perfusion; O2 carrying capacity; blood corpuscles; coronary tone; tracer digital radiography THE ISOLATED HEART MODEL USING crystalloid perfusates has been extensively used for characterizing myocardial contractility and energetics and the distribution of regional myocardial flows as well (5, 18, 49). However, most of the knowledge on regional crystalloid flows could not be extrapolated to explain the mechanisms of local regulation and coordination of regional myocardial flows under blood perfusion. Low O 2 carrying capacity of crystalloid perfusates makes an intracellular O 2 tension inadequate or just above the threshold for impaired myocardial function (6, 38) and reduces coronary tone or reserve (12,28,34). The distribution of regional myocardial flow is greatly under the influence of coronary tone (2, 5), and therefore there will be differences between spatial flow patterns in crystalloid-and blood-perfused myocardium. Furthermore, the presence or absence of blood corpuscles will augment those differences, because rheological, stochastic, and functional behaviors of corpuscles alter regional flows greatly at micr...

Changes to both cardiac metabolism and performance accompany acute reductions in functional capillary supply

“…Indeed, periods of reduced myocardial flow may be a normal cardiac phenomenon, largely controlled by arteriolar autoregulation [11]. Other factors may influence oxygen delivery beyond arteriolar dilatation, and hence perfusion.…”

“…Decreased perfusion of cardiac muscle and impaired coronary flow reserve may predict mortality in humans [10] with microvascular diseases such as diabetes [11], as a close correlation between oxygen demand and capillary distribution normally matches delivery with utilisation [19]. We therefore postulated that if microvascular units (an individual arteriole and its associated capillaries supplied downstream) are responsible for local provision of oxygen to the myocardium, loss of functional capillaries by occlusion of individual arterioles would decrease work performed by the heart, and hence decreased total metabolism, without altering the balance between lipid and glucose metabolism for the remaining muscle fibres as no 'spillover' of oxygen into adjacent capillary domains may occur.…”

Defects in myoglobin oxygenation in KATP-deficient mouse hearts under normal and stress conditions characterized by near infrared spectroscopy and imaging

“…(b) Oxygen diffusion from the vascular lumen to the cytoplasm may be heterogeneous due to variability in vascular permeability and diffusion distance between capillaries and myocytes [37]. The latter depends on the interstitial volume that is known to increase in crystalloid-perfused hearts due to edema [38], which again can be non-uniform. (c) Oxygen consumption is usually linearly dependent on cardiac workload, which may vary not only transmurally, but also longitudinally due to different mechanical stress for muscle fibers in different locations.…”

“…In this mode of acquisition, the contribution from the transmural layers that display greater microflow heterogeneity [38] was attenuated due to high absorbance, and scattering in the cardiac tissue. Additional factors, such as averaging of OSP over a 4-min interval, neglecting the small motion of the isovolumic hearts during the cardiac cycle, and perfusion of mouse hearts with buffer rather than blood (thus, at higher perfusion rates) likely resulted in an RD decrease [39].…”

Cardiac Hemodynamics, Coronary Circulation and Interventional Cardiology

“…24,32,81 Systolic compression of the vessels penetrating the myocardium was also observed by synchrotron radiation microangiography for dog and rat coronary arteries. 48,53 Thus, the subendocardial perfusion is under the major influence of cardiac contraction. Indeed, when the heart is arrested and the vascular vessels are fully dilated, the subendocardial perfusion becomes about 50% higher than at the subepicardium, which correlates with a higher vascular volume and stronger compressive force in the deeper myocardium.…”