New double-tracer digital radiography for analysis of spatial and temporal myocardial flow heterogeneity

Fluorescence imaging to quantify the fluorescent microspheres in cardiac tissue

To quantify the fluorescent microsphere (FM) content in cardiac tissue, which is an indicative of blood flow, fluorescence imaging of both sides of the pig heart slice was employed. Despite the light scattering inside the tissue and contributions from multiple tissue layers to the total emission, it is shown that the fluorescence intensity at any pixel is proportional to the FM content and the fluorescence image may be transformed to the image of the FM concentration. A convenient standard for the emission-FM concentration transformation is proposed. The approach has several advantages in comparison with the traditional "digestion & extraction" method such as: non-destructiveness, high spatial resolution, high throughput, repeatability and simplicity of operation.

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

Regional myocardial flow distributions in Langendorff rat hearts under Tyrode and blood perfusion were assessed by tracer digital radiography (100-μm 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 (642 pixels) and for coarse-grained images (322, 162, and 82 blocks of nearby pixels). At a given point in time during baseline, both CV and CA were higher in blood ( n = 7) than in Tyrode perfusion ( n = 7) over all pixel aggregates ( P < 0.05, two-way ANOVA). During the maximal hyperemia, CV and CA were still significantly higher in blood ( n = 7) than in Tyrode perfusion ( n = 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 = 7) showed a smaller CV and CA than those at a given point in time ( P < 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.

Commonly used numbers of microspheres affect cardiac vascular resistance

The main goal of the study was to examine how the microsphere technique affects the hemodynamics and mitochondrial energy status of the Langendorff-perfused rat heart. The hearts were perfused at a constant flow with Tyrode solution. NADH videofluorometry of the surface of the left ventricle was used to record the mitochondrial energy status as indication of regional ischemia. The effects of seven successive (separated by 10 min) injections of 0.1 ml of saline or (0.05% Tween 20; polysorbate 20, Sigma-Aldrich, St. Louis, MO, U.S.A.) or (0.05% Tween 20 + microspheres) were studied. The number of microspheres per injection were: #1 (2,500), #2 (5,000), #3 (10,000), #4 (20,000), #5 (40,000), #6 (40000), and #7 (80000). The anti-aggregation agent Tween always caused a biphasic response in perfusion pressure. Compared with the Tween effect, the injection of microspheres caused an initial change (mm Hg) in perfusion pressure of #1 (-10), #2 (NS), #3 (NS), #4 (+7.5), #5 (+12.3), #6 (+14.4), #7 (+18.3), and a delayed change (10 min after injection) of #1 (-22.2), #2 (-6.0), #3 (-4.1), #4 (-4.5), #5 (NS), #6 (NS), and #7 (+5.9). The microspheres caused a significant delayed increase in NADH only for injection #6 and #7. Similar results were found for different durations of the input function or when hearts were perfused at constant perfusion pressure. In hearts without flow reserve (10 microM adenosine), Tween injections were without effect, whereas three successive injections of 60,000 microspheres each only caused increases in perfusion pressure and NADH. The data demonstrate that in hearts with flow reserve present, even very low numbers of microspheres (2,000/g heart) cause large decreases in perfusion pressure without obvious signs of ischemia. When flow reserve was exhausted by either microsphere loading or adenosine addition, microspheres only caused increases in perfusion pressure and resulted in detectable ischemia (NADH). It is concluded that microspheres affect the vascular resistance of the heart and that these effects are flow reserve dependent.