Total Myocardial Flow Research Articles

Influence of pre-existing ischemia on recovery from chemical cardioplegia. A study on pig hearts in an isolated blood-perfused model.

The impact of prior cardiac ischemia on recovery from chemical cardioplegia was investigated in pig hearts. Group I hearts were subjected to 9-min normothermic ischemia before the start of chemical cardioplegia. After 180 min of induced cardiac arrest, all hearts were reperfused and monitored for 120 min in a blood-perfused Langendorff model. Consistent with left ventricular performance, myocardial oxygen uptake was significantly lower in group I than in the other hearts during the first 60 min of reperfusion. Lactate elimination was significantly higher in group I at the start of reperfusion, but showed no intergroup difference after 25 min. Nor was intergroup difference found in left ventricular end-diastolic pressure, total myocardial flow or glucose extraction fraction during reperfusion. The mitochondrial ultrastructure was identical in the two groups before chemical cardioplegia. During cardioplegia it deteriorated in group I but normalized in group II. During reperfusion these circumstances were reversed. Although precardioplegic ischemia thus significantly impaired left ventricular performance during early recovery, with corresponding effects on metabolism and ultrastructure, stable performance during reperfusion indicated that the ischemic injury did not worsen.

Stability of heterogeneity of myocardial blood flow in normal awake baboons.

Regional myocardial blood flow has been thought to be relatively uniform, in accord with the singular function of myocardial cells. However, considerable spatial heterogeneity has been observed in the hearts of anesthetized animals and in isolated hearts. Studies were undertaken in a total of 13 baboons. Eleven were awake, healthy animals sitting in chairs at rest or feeding, some performed mild leg exercise (wheel turning), and others were subjected to whole body heating; two were anesthetized, methodological controls. Microspheres (15 +/- 3 micron diameter, 0.5 X 10(6)/kg body weight) were injected via a catheter into the apex of the left ventricle while arterial blood was sampled at a constant rate for calculating cardiac output. Microspheres with different labels were injected at six intervals of 20 minutes to several hours. On sacrifice, the hearts were sectioned into 204 locatable pieces (left ventricle, 168; right ventricle, 27; and atria, 9). Average resting myocardial flow was 2.1 +/- 0.2 ml/g per min (mean +/- SD, n = 11). Left and right ventricles and atria comprised 70 +/- 2% (n = 13), 20 +/- 2%, and 10 +/- 2% respectively of the total heart mass while receiving 80 +/- 3%, 16 +/- 2%, and 4 +/- 2% of the total myocardial flow. Thus, mean left ventricular flow was 114 +/- 5% of the average for the whole heart, right ventricular flow was 81 +/- 13%, and atrial flow was 41 +/- 13%. Myocardial flow heterogeneity was marked; in left ventricle, regional flows ranged from one-third to two times the mean, the relative dispersion (= standard deviation/mean) of regional flows, corrected for methodological scatter and temporal variation, was 0.33 +/- 0.06 (n = 67) in the whole heart, 0.26 +/- 0.07 in left ventricle, 0.32 +/- 0.11 in right ventricle, and 0.22 +/- 0.19 in the atria. The pattern of regional flows in each heart tended to remain stable with time. In each piece averaged over time, the relative dispersion due to temporal heterogeneity was 0.11 +/- 0.03 (n = 2040) in the whole heart, 0.09 +/- 0.03 in the left ventricle, 0.15 +/- 0.05 in the right ventricle, and 0.23 +/- 0.06 in the atria. The conclusion is that the degree of spatial heterogeneity of local myocardial flows in conscious primates is similar to that of anesthetized animals and isolated hearts, and is much greater than that due to temporal fluctuations.

Total, phasic, and regional myocardial blood flow in aortic stenosis

The effect of aortic stenosis on total, phasic, and regional myocardial flow was studied in 16 anesthetized, open-chested dogs. An adjustable catheter device was used to produce increasing aortic obstruction, the severity of which was judged from the left ventricular aortic peak systolic gradient as mild (< 25 mm. Hg), moderate (26 to 50 mm. Hg) and severe (> 50 mm. Hg). The supply/demand index was estimated from the ratio of diastolic pressure time index to systolic pressure time index ( DPTI SPTI ). The ratio of diastolic to systolic coronary blood flow ( DIAS SYS ) was determined from the flow tracings. Total myocardial flow and endocardial/epicardial flow ratios ( ENDO EPI ) were determined by injecting four differently-labeled 7 to 9 micron microspheres in the left atrium during control, mild, moderate, and severe aortic stenosis. The supply/demand ( DPTI SPTI ) index decreased significantly at all levels of aortic stenosis because of a decrease in DPTI and an increase in SPTI. The DIAS SYS coronary flow ratio and the ENDO EPI myocardial flow ratio were not significantly changed during aortic stenosis. The total myocardial flow was significantly higher than control only during severe aortic stenosis. The results indicate that, for all degrees of experimental aortic stenosis, there were significant decreases in DPTI SPTI but no significant changes in DIAS SYS coronary flow ratio or the distribution of myocardial perfusion. Thus, in acute, experimental aortic stenosis, there is evidence of increased myocardial oxygen demand, but endocardial perfusion is not changed significantly.

Blood flow in sequential vein grafts.

In 69 patients undergoing coronary artery bypass grafting for complete coronary revascularization, blood flow was measured in 140 grafts with 243 distal anastomoses (3.52 bypasses/patient). Total blood flow in single grafts and double and triple sequential grafts did not differ significantly, although mean distal flow decreased successively with single (85 cc/min), double (51 cc/min), and triple (32 cc/min) sequential grafts. Total myocardial flow did not vary significantly regardless of the number of grafts placed. Flow measurements in patients with double sequential grafts showed greater than 20% overlay in flow between the two distal anastomoses. The data suggest significant but incomplete collateral supply between adjacent coronary beds consistent with the concept of any individual area of myocardium being a capacitance bed supplied in part by a number of adjacent coronary branches.

Total and regional myocardial blood flow in aortic regurgitation

Total, phasic, and regional flow were studied in 12 open-chest dogs with aortic regurgitation. An adjustable catheter device was used to produce aortic regurgitation. Four differently labeled 7 to 9μ microspheres were injected into the left atrium during control, mild (5 to 25 per cent), moderate (25 to 50 per cent), and severe (50 to 80 per cent) regurgitation. Aortic regurgitation (AR) and the ratio of diastolic coronary blood flow to systolic coronary blood flow ( DIAS SYS RATIO) were measured from the electromagnetic flow tracings. The simultaneous left ventricular and aortic pressures were used to calculate DPTI SPTI (diastolic pressure time index to systolic time index). Myocardial flow, flow to major subgroups, and endocardial/epicardial ratios were determined from radioisotope analysis of the left ventricle. Mean absolute control values and mean changes of key variables from control were: 3 Control Mild AR Mod AR Severe AR Heart rate (beats/min.) 163.42 −5.00 −4.83 ∗ −8.56 DPTI SPTI 1.18 −0.12 ∗ −0.24 ∗ −0.56 ∗ Dias/Sys ratio 4.23 −0.28 −1.64 ∗ −3.31 ∗ Myo. flow (ml./100g./min.) 99.90 −5.63 11.18 21.63 Endocardium (ml./100 g./min.) 97.27 −5.28 10.26 7.39 Epicardium (ml./100 g./min.) 100.15 −7.38 7.88 21.58 ENDO EPI ratio 0.99 0.01 0.01 −0.11 ∗ Denotes significant change from control state (P = 0.05). The phasic coronary blood flow results in this study are similar to those reported in chronic, intact anesthetized dogs; when the degree of aortic regurgitation increased, there was a significant decrease in diastolic coronary blood flow with an increase in systolic coronary blood flow. Not previously reported are the changes in the distribution of myocardial perfusion. Total myocardial flow increased slightly. There were minimal changes in blood flow to the endocardium which resulted in a slight decrease in the ENDO EPI ratio and a decrease in the per cent of flow to the endocardium. These results indicate that, although acute aortic regurgitation produces significant changes in phasic coronary flow, there are much smaller effects on total and regional myocardial blood flow.