Distribution of maximum coronary blood flow in the left ventricular wall of anesthetized dogs

Blood flow in the circumflex branch of the left coronary artery was recorded by electromagnetic flowmeter. In a group of dogs progressive hemodilution was performed until the diastolic reactive hyperemic response to 10 s occlusion of the circumflex branch disappeared (“optimum” hemodilution). At this degree of hemodilution the distribution of blood flow in the left ventricular free wall was evaluated by measuring tissue activity concentrations of Xe-133 and radioactive microspheres after bolus injection into the aortic root. “Optimum” hernodilution was accompanied by a sixfold increase in systolic coronary flow, a 3-fold increase in diastolic flow and a relative endocardial hypoperfusion. These results indicate that the endocardial blood flow reserve is lower than the epicardial. This conclusion is supported by the influence of spontaneous oscillations of arterial blood pressure (Traube-Hering waves) on systolic and diastolic coronary blood flows before and during “optimum” hemodilution. In another group of dogs maximum coronary vasodilatation was produced by occlusion of the left coronary artery for 10 s. In this group the distribution of Xe-133 and radioactive microspheres were measured after bolus injection into the aortic root at peak diastolic reactive hyperemia. The epi- and endocardial distribution of both Xe-133 and microspheres was uniform in the left ventricular wall, indicating a uniform flow to these regions. This might be explained by an increased endocardial perfusion during systole due to loss of myocardial contractility or by a decline towards resting level in epicardial flow at the time of injection, corresponding to a shorter duration of the hyperemic period in the epi- than endocardial region.     

Regional Blood Flow in the Left Ventricular Wall of Dogs with a Graded Coronary Artery Stenosis

Blood flow in the circumflex branch of the left coronary artery was recorded by electromagnetic flowmeter. In the area supplied by this branch vasodilatation was produced by progressive constriction until the diastolic reactive hyperemic response to 10 s occlusion disappeared (“optimum” stenosis). This degree of stenosis was accompanied by a 20% decrease in diastolic circumflex flow, while systolic flow remained unchanged. The distribution of blood flow in the left ventricular free wall was evaluated at “optimum” stenosis by counting activity in tissue blocks following bolus injection of Xe-133 into the aortic root. When Xe-133 was injected immediately after occlusion of the left anterior descending branch the Xe-133 concentration of the endocardial part of the area supplied by the circumflex branch was about half the concentration in the epicardial part. The concentrations in the two parts did not, however, differ significantly when occlusion of the left anterior descending branch was omitted. This indicates that the endocardial blood flow reserve is lower than the epicardial, and that, yet, a preferential fall in blood flow in the endocardial part of a post-stenotic area can be rapidly eliminated when blood supply from a neighbouring artery is available.     

Distribution of coronary blood flow in the left ventricular wall of dogs evaluated by the uptake of Xe-133.

The distribution of coronary blood flow was estimated in anesthetized dogs by counting the activity in tissue blocks of the left ventricular free wall immediately after bolus injection of Xe-133 into the aortic root. No differences in the uptake of isotope were observed between the apex and the base of the heart; between areas supplied by the anterior descending and circumflex branches of the left coronary artery; or between the endo- and epicardial halves of the wall. In most experiments a bolus injection of the isotope into the left coronary artery was followed by a difference in activity between areas supplied by the left anterior descending and left circumflex branches. This indicated inadequate mixing of blood and isotope in the main stem of the artery. The uneven distribution did not result in differences between the epi- and endocardial activity concentrations. The results from one normal, anesthetized dog in which tissue activities were measured after constant rate infusion of Xe-133 into the left coronary artery for 8 min were in accordance with the general assumption of equal epi- and endocardial volumes of distribution (values of lambda).     

Distribution of Coronary Blood Flow in the Left Ventricular Wall of Dogs Evaluated by the Uptake of Xe-133

The distribution of coronary blood flow was estimated in anesthetized dogs by counting the activity in tissue blocks of the left ventricular free wall immediately after bolus injection of Xe-133 into the aortic root. No differences in the uptake of isotope were observed between the apex and the base of the heart; between areas supplied by the anterior descending and circumflex branches of the left coronary artery; or between the endo- and epicardial halves of the wall. In most experiments a bolus injection of the isotope into the left coronary artery was followed by a difference in activity between areas supplied by the left anterior descending and left circumflex branches. This indicated inadequate mixing of blood and isotope in the main stem of the artery. The uneven distribution did not result in differences between the epi- and endocardial activity concentrations. The results from one normal, anesthetized dog in which tissue activities were measured after constant rate infusion of Xe-133 into the left coronary artery for 8 min were in accordance with the general assumption of equal epiand endocardial volumes of distribution (values of Zs).     

Methodological Aspects of Testicular Blood Flow Measurements in Rats

3 techniques for the measurement of testicular blood flow in anesthetized adult rats were compared. Direct measurement of testicular venous outflow yielded values more than 3 times lower than those obtained by Xe-133 clearance and radioactive microsphere techniques due to the surgical procedures involved in spermatic venous cannulation. There was an agreement between flow values obtained with Xe-133 clearance (17.8 ± 3.5 ml/100 g×min) and radioactive microspheres (19.9 ± 5.5 ml/100 g×min). A homogeneous distribution of microspheres to different segments of the testis indicates that Xe-133 clearance is an adequate technique for testicular blood flow measurements. However, for some experimental purposes the radioactive microsphere technique is more versatile than Xe-133 clearance because of its capacity of measuring several organ flows simultaneously.     

Measurement of local blood flow in acute myocardial infarction: loss of 15-micron microspheres during the first hour

Distribution of radiolabelled microspheres is widely utilized for determination of regional blood flow in experimental myocardial infarction studies. The purpose of this investigation was evaluation of the microsphere method during 1 h of regional ischaemia. Special attention was focused upon loss of preocclusion microspheres from ischaemic myocardium; mechanisms for loss and blood flow distribution in non-ischaemic left ventricle. Microspheres (15 micron) were injected into the left atrium in nine pentobarbital anaesthetized cats prior to coronary artery occlusion and again after 1 h of occlusion. Preocclusion blood flow estimates were lower in ischaemic compared with non-ischaemic myocardium (1.36 vs. 1.62 cm3 X min-1 X g-1, P = 0.002), corresponding to 16% apparent loss. In endocardial ischaemic tissue, development of oedema could account for the loss. In epicardial ischaemic tissue, oedema was not present and loss was therefore due to migration of microspheres. Epicardial loss increased in proportion to restoration of left ventricular contractility. There was no evidence for significant microsphere loss through lymphatic pathways. In non-ischaemic left ventricular tissue, myocardial blood flow was evenly distributed from apex to base, and also between endocardial and epicardial layers. This study quantitates an important limitation to measurements of local blood flow in ischaemic myocardium by radiolabelled microspheres.     

Measurement of local blood flow in acute myocardial infarction: loss of 15-^m microspheres during the first hour

Distribution of radiolabeled microspheres is widely utilized for determination of regional blood flow in experimental myocardial infarction studies. The purpose of this investigation was evaluation of the microsphere method during 1 h of regional ischaemia. Special attention was focused upon loss of preocclusion microspheres from ischaemic myocardium; mechanisms for loss and blood flow distribution in non-ischaemic left ventricle. Microspheres (15 μm) were injected into the left atrium in nine pentobarbital anaesthetized cats prior to coronary artery occlusion and again after 1 h of occlusion. Preocclusion blood flow estimates were lower in ischaemic compared with non-ischaemic myocardium (1.36 us. 1.62 cm³min^-1 g^-1, P = 0.002), corresponding to 16%apparent loss. In endocardial ischaemic tissue, development of oedema could account for the loss. In epicardial ischaemic tissue, oedema was not present and loss was therefore due to migration of microspheres. Epicardial loss increased in proportion to restoration of left ventricular contractility. There was no evidence for significant microsphere loss through lymphatic pathways. In non-ischaemic left ventricular tissue, myocardial blood flow was evenly distributed from apex to base, and also between endocardial and epicardial layers. This study quantitates an important limitation to measurements of local blood flow in ischaemic myocardium by radiolabelled microspheres.     

Relations between collateral flow and tissue salvage in the risk area after acute coronary occlusion in dogs: a topographical analysis.

Localization of salvaged tissue after occlusion of the left anterior descending coronary artery due to collateral blood flow within the risk area was examined in a canine model using differential autoradiography. 125I tracer microspheres were injected into the left anterior descending artery preocclusively to define the perfusion territory as a risk area. 99mTc labelled human serum albumin microspheres were injected into both the left main and right coronary arteries 48 h after ligation to determine the collateral flow area. Using a cryotome, 50 micron transverse sections of the whole heart were taken, and 125I and 99mTc autoradiograms were obtained independently. The same specimens were stained by the nitroblue-tetrazolium method to demarcate the intact and infarcted myocardium. The tracings of the infarct, risk and collateral areas were compared and measured by a plainmeter. The collateral blood flow was distributed to 86, 55 and 42% of the epi, mid- and endo-cardial portions of the risk area respectively (P less than 0.001 between the epi- and mid- or endo-cardium). Within the collateral area 88, 58 and 63% of the epi-, mid- and endo-cardial portions were free of myocardial necrosis (P less than 0.001 between the epi- and mid- or endo-cardium). There was a close linear relationship between the size of salvaged and collateral areas (r = 0.96, P less than 0.001). Thus, a topographical analysis of the tissue salvage inside the risk area demonstrated the indispensable role of collateral blood flow for maintaining tissue viability.     

Relations between collateral flow and tissue salvage in the risk area after acute coronary occlusion in dogs: a topographical analysis

Localization of salvaged tissue after occlusion of the left anterior descending coronary artery due to collateral blood flow within the risk area was examined in a canine model using differential autoradiography. 125I tracer microspheres were injected into the left anterior descending artery preocclusively to define the perfusion territory as a risk area. 99mTc labelled human serum albumin microspheres were injected into both the left main and right coronary arteries 48 h after ligation to determine the collateral flow area. Using a cryotome, 50 micron transverse sections of the whole heart were taken, and 125I and 99mTc autoradiograms were obtained independently. The same specimens were stained by the nitroblue-tetrazolium method to demarcate the intact and infarcted myocardium. The tracings of the infarct, risk and collateral areas were compared and measured by a plainmeter. The collateral blood flow was distributed to 86, 55 and 42% of the epi, mid- and endo-cardial portions of the risk area respectively (P less than 0.001 between the epi- and mid- or endo-cardium). Within the collateral area 88, 58 and 63% of the epi-, mid- and endo-cardial portions were free of myocardial necrosis (P less than 0.001 between the epi- and mid- or endo-cardium). There was a close linear relationship between the size of salvaged and collateral areas (r = 0.96, P less than 0.001). Thus, a topographical analysis of the tissue salvage inside the risk area demonstrated the indispensable role of collateral blood flow for maintaining tissue viability.     

The effect of chronic hypoxemia on regional myocardial blood flow in the conscious dog after acute coronary artery occlusion

Chronic hypoxemia was produced in 16 dogs by surgical transposition of the caudal vena cava to the left atrium to determine if chronic hypoxemia would alter the response of the myocardium to acute ischemia. An electromagnetic aortic flow probe, left atrial tube, and occlusive cuff on the left circumflex coronary artery were permanently implanted in 11 hypoxemic and 26 normal control dogs. The animals were studied in the conscious state after recovery from the surgery. Dogs with hypoxemia had a blood hematocrit value of 54.3 ± 1.0% (SE), arterial PO₂ of 43.2 ± 1.4 mm Hg, and 80.2 ± 1.6% oxygen saturation. There was no difference from control animals in the ratio of left ventricular weight to body weight, but the right ventricular weight was significantly decreased in the hypoxemic dogs. Cardiac output from the left ventricle was twice that of the right ventricle. Aortic blood flow was 3.68 ± 0.22 liters/min in hypoxemic animals and 2.64 ± 0.19 liters/min in normal dogs. Myocardial blood flow measured with 15-μ diameter tracer microspheres was increased from 79 ± 10 and 59 ± 8 ml/100 g/min in left ventricular endocardial and epicardial halves, respectively, in normal dogs to 212 ± 48 and 172 ± 39 in dogs with chronic hypoxemia. There were no deaths in 10 hypoxemic dogs within 24 hours after complete circumflex coronary artery occlusion; 7 of 26 (27%) normal dogs died after circumflex coronary artery occlusion during the conscious state. Gross infarct size was extremely variable in both groups. Median infarct size was smaller in dogs with hypoxemia and was directly correlated with arterial PO₂ in hypoxemic dogs. There was a mild, but statistically not significant, increase in the anastomotic index of hypoxemic dogs compared with that of normal animals, suggesting that a metabolic adaptive change rather than increased collateral circulation may have been responsible for the decreased mortality and smaller infarct size in hypoxemic dogs.     

急性缺血心肌的血流量再分布

利用放射性生物微球技术,研究了犬在急性心肌缺血时,侧支循环血流量的再分布,在结扎左前降支冠脉后,中心缺血区血流量明显减少。近边缘区血流量大于中心缺血区血流量,小于远边缘区和非缺血区的血流量。中心缺血区和近边缘区的心内膜下层心肌血流量低于心外膜下层心肌血流量,两者之比小于1.00。随着缺血时间的延长(1—6小时),中心缺血区血流量逐渐减小,而非缺血区的血流量逐渐增加。     

Regional perfusion in hearts with acute coronary artery occlusion and subsequent beta 2- and alpha 1-adrenergic blockade

Blockade of cardiac adrenoceptor subtypes, coronary or myocardial, might elicit compensatory interaction from remaining unblocked subtypes. An attempt to explore this interplay was made by studying regional myocardial blood flow alterations associated with beta 2-adrenergic blockade followed by alpha 1-adrenergic blockade in anaesthetized cats with acute coronary occlusion. In order to maintain constant needs for perfusion, atrial pacing was established and the aortic blood pressure was kept constant. In myocardium remote from the ischaemic region, beta 2-adrenergic blockade produced higher endocardial blood flow whereas no flow changes were observed close to the ischaemic region. With subsequent alpha 1-adrenergic blockade, blood flow increased endocardially in non-ischaemic regions, but remained unchanged in epicardial tissue. Control experiments without coronary ligation revealed no increase in left ventricular oxygen consumption during the experiments and support the theory that the observed blood flow increase in the coronary ligation group, following drug interventions, was not caused by increased cardiac work. This study indicates that combined beta 2- and alpha 1-adrenergic blockade alters the balance between receptor subtypes. Unopposed beta 1-mediated vasodilation is the most likely candidate to explain why endocardial flow was increased.     

The effect of hemodilution with fluorocarbon or dextran on regional myocardial flow and function during acute coronary stenosis in the pig

The effect of replacement of approximately 50% of the blood volume, in the presence of critical coronary stenosis, was investigated in anesthetized pigs. Two agents were used for replacement: 6% dextran 70 and Fluosol-DA, a fluorocarbon "blood substitute," capable of transporting oxygen by virtue of its high solubility. Critical coronary stenosis of 15-min duration was imposed on the circumflex coronary artery by means of a micrometer snare, before and after an exchange-transfusion with one of the above acellular agents, resulting in comparable reductions of myocardial blood flow (determined by microspheres) to the circumflex zone. In the ischemic zone, systolic wall-thickening (as determined by sonomicrometry) was reduced by 62 +/- 10% in the dextran-diluted pigs, but only by 33 +/- 7% in the Fluosol-diluted pigs (p less than .05). Estimated oxygen delivery-rate in this zone, during coronary constriction, was 6.2 and 7.5 ml min-1 100 g-1, respectively. Electron microscopic examination of the normally perfused zone of the heart showed no morphological change attributable to Fluosol. The findings suggest that, in the presence of critical coronary stenosis, hemodilution by Fluosol-DA can be tolerated, while similar hemodilution with dextran results in aggravation of myocardial hypoxia. In three instances, severe reactions were observed immediately following the administration of Fluosol. These were suggestive of complement-activation and were excluded from the analysis.     

The radioactive microsphere method for the assessment of regional myocardial blood flow after coronary artery occlusion

In this study, we have tried to determine the magnitude of the inaccuracy of the radioactive microsphere method - due to variations in the diameter distribution of the spheres - for measuring regional myocardial blood flow after coronary artery occlusion. In 5 mongrel dogs, three types of 15 mum microspheres, labelled with 125I, 141Ce or 85Sr, were injected simultaneously after the descending branch of the left coronary artery had been ligated. Myocardial samples wert taken from the left ventricle and divided into four groups according to the number of spheres per sample. The radioactivity of the various isotopes per gram tissue was expressed as percentage of their activity per milliliter of the reference sample. The diameter distribution of microspheres, labelled with each of the isotopes, was determined light-microscopically in suspensions belonging to three different batches. The relative error, as determined from the difference in relative radioactivity of the various types of microspheres in the tissue samples, was higher than the theoretical error for each of the number of spheres per sample. It is very likely that this discrepancy is caused by the differences in diameter distribution of the various types of microspheres, resulting in non-random error. The smaller spheres tended to go to low flow areas and the larger ones to high flow areas. Because of the non-randomness, the error due to diameter variations in the spheres can be diminished by randomizing the order of injection of the various isotopes. The present study indicates that the relatively high degree of accuracy of the microsphere method for the determination of blood flow to large parts of the myocardium with an unimpeded coronary circulation, as was described in literature, cannot be extrapolated to the determination of regional myocardial blood flow after coronary artery occlusion, when the combination of small tissue samples, variations in the diameter distribution of the spheres and an unevenly distributed myocardial blood flow unfavourably affect the accuracy of the method.     

The intracarotid 133xenon injection method for measurement of cerebral blood flow (CBF) in rats: evaluation of the effect of bolus volume

It is assumed that the cerebral microcirculation is not perturbed by the intraarterial injection used in determination of cerebral blood flow (CBF) with the intraarterial 133Xenon technique (and in various assessments of blood brain barrier (BBB) permeability). The application of these techniques to the rat, where the injectate is large compared to normal blood flow, places this problem is focus and it has been claimed that since large intracarotid injections increased cerebral venous outflow, the CBF must also increase. We investigated this problem in the rat by means of the intraarterial 133Xenon injection technique, using a saline bolus injected in less than 1 sec and found that CBF was unaltered at bolus volumes between 10 and 100 microliters. Furthermore, injection of 100-200 microliters saline during washout detection did not change the slope of the semilogarithmic wash-put curves. It is concluded that in spite of large intracarotid injections the CBF remained constant and that the hemodilution produced by the saline bolus is not sufficient to influence CBF. Consequently, estimations of CBF yield valid results in the present rat preparation.     

Does alpha 1-adrenergic blockade influence regional blood flow regulation in hearts with coronary artery occlusion?

The effects of selective alpha 1-adrenergic blockade with doxazosin on regional myocardial tissue blood flow was studied in anaesthetized cats with acute coronary artery occlusion. Reflex tachycardia was prevented by selective beta 1-adrenergic blockade with atenolol and coronary perfusion pressure was kept constant by partial stenosis of the descending aorta. Administration of atenolol reduced cardiac mechanical work-load by its negative inotropic and chronotropic effects, and reduced myocardial tissue blood flow in normally perfused myocardium. This reduction was most pronounced in the endocardial half-layer of the myocardium adjacent to the ischaemic region. Administration of doxazosin in this situation clearly reduced peak systolic and coronary perfusion pressure. But when coronary perfusion pressure was raised to pre-administration values, measurements of regional blood flow revealed no changes either in ischaemic or non-ischaemic myocardium. Also, there was no sign of redistribution of blood flow between endocardial and epicardial tissue in any area. This study, therefore, indicates that alpha 1-adrenoceptors play a minor role in the regulation of coronary blood flow in normal myocardium as well as ischaemic myocardium.     

柳胺苄心定对急性心肌梗塞家兔心肌血流量梗死范围及左室功能的影响

本文观察了兼有α_1受体阻断作用的β受体阻断剂柳胺苄心定(labetalol,简称Lab)对急性心肌梗塞家兔心肌血流量(放射性微球法),梗死范围及左室功能的影响,并与心得安比较。结果表明:小剂量Lab(1mg/kg)主要显示β受体阻断效应,它能减慢心率,降低心肌耗氧量,降低非梗死区心肌血流量,缩小梗死范围,其效应与心得安相似,且能改善左室舒缩功能;大剂量Lab(5mg/kg),能同时阻断α_1和β受体,它能降低动脉血压,相对增加各区心肌血流量,显著减少心肌耗氧量,缩小梗死范围。结果提示:在急性心肌梗塞治疗中,同时阻断α_1和β受体较单纯阻断β受体优越。     

Excess cumulative blood flow and repayment during reactive hyperemia in human cutaneous tissue

The influence of duration of vascular occlusion upon the reactive hyperemic response in human cutaneous tissue was studied in 6 subjects. Blood flow in cutaneous tissue was measured dorsally on the distal phalanx of the second finger by the local ¹³³Xenon washout technique. Post-occlusive blood flow, calculated from the steepest part of the ¹³³Xenon washout curve just after release of vascular occlusion, reached a maximum value when duration of vascular occlusion was 12 min. However, excess cumulative blood flow, i.e. the integrated blood flow during reactive hyperemia minus integrated pre-ischemic blood flow for a period corresponding to the duration of the reactive hyperemic response, increased with increasing duration of vascular occlusion from 3 to 24 min. Fractional repayment, i.e. excess cumulative blood flow divided by pre-ischemic blood flow times duration of vascular occlusion, was not correlated significantly to duration of vascular occlusion. However, there was a significant inverse correlation between fractional repayment and pre-occlusive blood flow, indicating that, besides metabolic factors, pre-ischemic blood flow in cutaneous tissue is influenced by other factors, such as heat regulation.     

Effect of increased blood fluidity through hemodilution on coronary circulation at rest and during exercise in dogs

Summary Coronary flow and myocardial oxygen consumption were measured in conscious dogs at rest and during two levels of submaximal treadmill exercise (3 and 7 km/h at 15% grade, respectively) during adaptation to progressive hemodilution with dextran 60. At rest coronary flow increased to more than seven-fold with diminishing hematocrit to 12.5% in order to cover myocardial oxygen consumption which increased from 6.5±0.3 ml/min· 100 g at hematocrit 47.5% to 13.5±0.8 ml/min· 100 g at hematocrit 12.5%. The dilatory capacity of the coronary vessels, estimated from the reactive hyperemia after a 12 sec occlusion of the left circumflex coronary artery, dropped from 602% at control to 45% at lowest hematocrit levels.During the superimposed stress of exercise coronary flow and myocardial oxygen consumption increased further, so that the dilatory capacity of the coronaries was exhausted at hematocrit levels between 16 and 22%.Myocardial oxygen consumption per unit of oxygen delivered to peripheral tissues increased substantially with progressive hemodilution. In the presence of the reduced arterial oxygen content the augmented myocardial oxygen demand limits the overall adaptability to hemodilution by an exhaustion of the coronary dilatory capacity.Supported by Deutsche Forschungsgemeinschaft.     

Abnormal myocardial fluid retention as an early manifestation of ischemic injury.

Fifty-seven isolated, blood perfused, continuously weighed canine hearts have been utilized to study the development of abnormal myocardial fluid retention during early myocardial ischemic injury. Inflatable balloon catheters were positioned around the left anterior descending coronary arteries (LAD) of 54 hearts or the proximal left circumflex coronary arteries of three hearts for study of the following intervals of coronary occlusion: a) 10 minutes followed by 20 minutes of reflow, b) 40 minutes followed by either no reflow or by 20 minutes of reflow, and c) 60 minutes without reflow. After 60 minutes of fixed coronary occlusion, histologic and ultrastructural examination revealed mild swelling of many ischemic cardiac muscle cells in the absence of interstitial edema, cardiac weight gain, and obvious structural defects in cell membrane integrity. After 40 minutes of coronary occlusion and 20 minutes of reflow, significant cardiac weight gain occurred in association with characteristic alterations in the ischemic region, including widespread interstitial edema and focal vascular congestion and hemorrhage and swelling of cardiac muscle cells. Focal structural defects in cell membrane integrity were also noted. The development of abnormal myocardial fluid retention after 40 minutes of LAD occlusion occurred in association with a significant reduction in sodium-potassium-ATPase activity in the ischemic area, but with no significant alteration in either creatine phosphokinase or citrate synthase activity in the same region. Despite the abnormal myocardial fluid retention in these hearts, it was possible pharmacologically to vasodilate coronary vessels with adenosine and nitroglycerin infusion to maintain a consistently high coronary flow following release of the coronary occlusion after 40 minutes and to even exceed initial hyperemic flow values following release of the occlusion when adenosine and nitroglycerin infusion was delayed until 15 minutes after reflow. Thus, the data indicate that impaired cell volume regulation and interstitial fluid accumulation and focal structural defects in cell membrane integrity are early manifestations of ischemic injury followed by reflow, but fail to establish a major role for the abnormal fluid retention in altering coronary blood flow prior to the development of extensive myocardial necrosis. In contrast, fixed coronary occlusion for 60 minutes results in mild intracellular swelling but no significant interstitial edema and no obvious structural defects in cell membrane integrity.