Measurement Of Regional Flow Research Articles

Clinical relevance of myocardial ?stunning?

Experimental studies have demonstrated that myocardium reperfused after reversible ischemia exhibits prolonged depression of contractile function ("stunning"). Despite the multiplicity of clinical situations in which myocardial stunning would be expected to occur, investigation of this phenomenon in humans has been hindered by several major problems, including the limited accuracy of the methods available to measure regional left ventricular function, the inability to quantify regional myocardial blood flow during acute ischemia, the difficulty in establishing with certainty, the beginning and end of an ischemic episode, and the uncontrolled influence of variables (such as preload, afterload, adrenergic tone, and inotropic therapy) that have a major impact on postischemic dysfunction. The main problem is to discern whether a reversible defect of contractility is caused by stunning, silent ischemia, or hibernation (i.e., chronic ischemia). This differential diagnosis requires the simultaneous measurement of regional myocardial function and flow, which thus far has not been generally possible. Despite these limitations, however, numerous clinical observations suggest that stunning does occur in various settings in which the myocardium is exposed to transient ischemia, including coronary angioplasty, exercise-induced angina, angina at rest (unstable or variant), acute myocardial infarction with early reperfusion, open-heart surgery, and cardiac transplantation. Recognition of this entity is important, amongst other reasons, because it is likely to cause significant morbidity and because it is potentially correctable with inotropic therapy or even preventable with antioxidant therapy. In addition, the appreciation of the phenomenon of myocardial stunning should allow the clinician to assess the efficacy of reperfusion therapy with greater accuracy and to recognize that patients should not be denied mechanical revascularization solely because of an abnormal left ventricular wall motion. Perhaps the most intriguing clinical implication of the concept of myocardial stunning is the possibility that in patients who exhibit frequent episodes of ischemia in the same territory, the myocardium may not be able to fully recover between episodes and thus may remain reversibly depressed for prolonged periods of time, or even chronically, which could account for some cases of "ischemic cardiomyopathy." Our understanding of myocardial stunning in humans is still relatively crude and will not significantly improve until studies are performed that measure simultaneously regional myocardial perfusion and function (so that stunning can be differentiated from silent ischemia and hibernation). Future important areas of research should also include the elucidation of whether stunning can become chronic and the evaluation of therapies (such as antioxidant treatments) designed to prevent this contractile abnormality.(ABSTRACT TRUNCATED AT 400 WORDS)

Disturbances of speech prosody following right hemisphere infarcts

The ability to perceive and express emotional, as well as number of linguistic prosodic qualities of speech was tested in 20 Swedish-speaking patients with right-sided cortical, as well as purely subcortical brain infarcts, and in 18 normal controls. The infarcts were assessed by clinical neurological examination, and by CT, EEG, and measurements of regional cerebral blood flow (rCBF). In the patients the identification of emotional messages was disturbed, as well as the identification and production of several linguistic prosodic qualities. The study supports the claim that prosodic impairment could be linguistic in nature, and not secondary to affective disorder. The total degree of anatomical and functional disturbance of the right hemisphere played a role for both the ability to identify emotional messages and for identification of two of the linguistic prosodic qualities tested. However, it was not possible to find support for the hypothesis that the organization of prosody in the right hemisphere mirrors that of propositional speech on the left side.

Effects of brief coronary occlusion and reperfusion on porcine coronary artery reactivity.

The loss of coronary vasodilator reserve after ischemia-reperfusion may be due to endothelial injury, and this vascular dysfunction may contribute to functional alterations observed after ischemia. To determine whether endothelial dysfunction occurs after relatively brief periods of moderate low-flow ischemia in vivo, open-chest swine were subjected to 15 minutes of critical, subtotal left anterior descending coronary artery occlusion (80%) followed by 60 minutes of reperfusion. Serial measurements of regional coronary flow were made with the radiolabeled microsphere technique. After 60 minutes of reperfusion, the left anterior descending coronary artery was excised together with a section of the normally perfused left circumflex coronary artery to examine in vitro the relaxations to the endothelium-dependent dilators ADP and bradykinin and to the endothelial-independent dilators sodium nitroprusside and adenosine. Contractions to serotonin in quiescent rings were also examined. Endocardial and transmural blood flows recovered to preocclusion levels within 60 minutes of reperfusion, as did the epicardial-to-endocardial ratio. Vascular responses in isolated, reperfused left anterior descending coronary artery rings were significantly different from responses in control left circumflex coronary artery rings. Endothelium-dependent relaxations to adenosine diphosphate and bradykinin were significantly depressed in the left anterior descending coronary artery rings compared with left circumflex coronary artery rings (p less than 0.05). Serotonin-induced contractions were significantly greater in occluded-reperfused left anterior descending than in left circumflex coronary arteries (p less than 0.05). Relaxations to adenosine and sodium nitroprusside were not significantly different between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneities in regional volumes of distribution and flows in rabbit heart

The heterogeneity of volumes of distribution in the heart influences the rates of uptake and washout of substrates and metabolites; thus it is important to evaluate their variability in the normal heart. Several tracers were injected intravenously into anesthetized adult closed-chest rabbits, and time was allowed for equilibration in the heart. Tracer microspheres were injected into the left ventricular cavity at the apex for the measurement of regional flows, the chest was opened, another set of microspheres was injected, and the heart was frozen rapidly in situ with liquid nitrogen-cooled Freon-22. Each heart was divided into 72 pieces of less than 0.1 g weight, and the tracer content of each was determined by multichannel gamma-counting and the water content by desiccation. The regional myocardial flows were (closed chest) 0.62 +/- 0.16 ml.g-1.min-1 and (open chest) 0.63 +/- 0.37 ml.g-1.min-1. The volumes of distribution (ml/g) for the 432 pieces for six rabbits, given as mean +/- SD (% coefficient of variation), were as follows: for plasma, VP = 0.11 +/- 0.03 (26%); erythrocytes, VRBC = 0.041 +/- 0.015 (37%); vascular space, VV = 0.15 +/- 0.04 (26%); extracellular space, VECF = 0.33 +/- 0.05 (15%); interstitial space, VISF = 0.21 +/- 0.03 (15%); and water space, VW -0.79 +/- 0.022 (2.8%). Regional hematocrits were 77% +/- 9% of the large-vessel hematocrits.

Cardiac Secretion and Renal Clearance of Atrial Natriuretic Peptide in Normal Man: Effect of Salt Restriction

1. Previous studies of endogenous atrial natriuretic peptide (ANP) in humans have examined changes in plasma levels, rather than regional secretion and clearance of the peptide. Using arterial and selective venous catheterization and sampling, and measurement of regional organ flow, we measured haemodynamics, cardiac secretion of ANP and renal clearance of ANP in six healthy volunteers at rest, on a normal sodium diet. 2. Salt restriction decreases plasma concentrations of ANP. We assessed the contribution of the heart and kidney to this decrease, by measuring cardiac secretion and renal clearance of ANP at the termination of a low salt diet. 3. Twenty-four hour urinary sodium excretion fell on the low salt diet from 163 to 29 mmol/day [standard error of the difference (SED)+/- 14, P less than 0.001]. Body weight decreased on salt restriction from 76.4 to 75.4 kg (SED +/- 0.33, P less than 0.05). Brachial mean arterial pressure fell by 6% (P less than 0.05), but right atrial pressure was unchanged. Renal vein plasma renin activity increased by 56% with sodium restriction (P less than 0.01), whereas arterial ANP concentrations fell by 39% (P less than 0.05). 4. Coronary sinus ANP levels fell from 417 to 268 pg/ml (SED +/- 74, P less than 0.05), whereas renal vein concentrations were unaltered. There was a 47% decrease in cardiac secretion of ANP in the low salt state (P less than 0.05). Net extraction of ANP across the kidney (about two-thirds) and renal clearance of ANP were unchanged on the low salt diet. Thus decreased plasma ANP with sodium restriction is due to reduced cardiac secretion.

Effect of indomethacin on regulation of juxta-articular bone blood-flow during joint tamponade. An experimental study in puppies

Prostaglandins are vasoactive substances which are assumed to play a major role in bone metabolism and bone repair. The purpose of the present study was to investigate the effect of indomethacin on the control of epiphyseal bone blood-flow. By means of simultaneous intra-osseous pressure (IOP) and regional blood flow (RBF) measurements in the distal femoral epiphysis (DFE), aspects of vascular control mechanisms in the distal femoral epiphysis were investigated during knee joint tamponade (50% of mean arterial pressure) before and after administration of indomethacin 7.5 mg/kg. Six dogs aged 3-4 months were investigated in fentanyl anaesthesia. Knee joint tamponade resulted in a significant increase in IOP and calculated venous resistance in the DFE, while no significant changes in regional blood-flow or arterial resistance were encountered. Administration of indomethacin did not affect this reaction. The results suggests that indomethacin 7.5 mg/kg does not influence the regulation of epiphyseal blood-flow during elevation of joint pressure indicating that prostaglandins play only a minor or no role in this regulation.

Effect of reperfusion on O2 supply/consumption balance in ischemic canine left ventricle.

This study was designed to assess the effects of reperfusion on regional O2 supply and O2 consumption of ischemic areas of the myocardium in 15 anesthetized open-chested dogs. The left anterior descending coronary artery (LAD) was occluded for 6 h (n = 8), 2 h (n = 5), 2-h occlusion followed by 4-h period of reperfusion (n = 7), and 10-min occlusion followed by 90-min period of reperfusion (n = 3). Small artery and vein O2 saturations obtained microspectrophotometrically were combined with regional flow measurements using radioactive microspheres to determine regional myocardial O2 consumption. Coronary occlusion for 2 or 6 h significantly reduced mean flow to 15 +/- 8 and 13 +/- 14 ml/min/100 g (mean +/- SD), respectively, in the affected LAD areas as compared to 128 +/- 26 and 113 +/- 46 ml/min/100 g in the non-ischemic areas. In the 4-h reperfusion group, reperfusion increased the average flow (60 +/- 42 ml/min/100 g). O2 extraction was greater in the ischemic area than in the unaffected area after both occlusion and 4-h reperfusion. In the affected area, O2 consumption was reduced by 84% after 6-h occlusion. Reperfusion for 4 h increased O2 consumption toward normal values. Coronary artery occlusion produced an increase in the number of arteries and veins with reduced O2 saturations and this was not affected by reperfusion. Short-term occlusion had no significant O2 supply effects after 90 min of reperfusion. It can be concluded that even though there was an increased O2 consumption as a consequence of reperfusion, O2 consumption still appeared to be flow-limited as indicated by the microregions of low O2 supply and/or high O2 extraction.

Cardiac nuclear medicine, present status, future hopes as seen from the view of a cardiologist

The present techniques of nuclear medicine that are used in cardiology are critically evaluated. They are used mainly for the assessment of coronary circulation (measurement of regional flow and perfusion), on the determination of left ventricular muscle function (radionuclear ventriculography) and on the study of cardiac metabolism. The last-mentioned technique is unique insofar as (except for magnetic resonance imaging) there is no other method available to analyse myocardial metabolism noninvasively in living man. Of immense practical importance is the diagnosis and quantitation of the abnormal coronary flow and perfusion, as coronary artery disease is one of the major diseases of the Western world. Finally, the value of nuclear imaging techniques is compared with that of other nonnuclear methods. In present-day medicine, with its increasingly high costs, the value of nuclear techniques must be assessed very carefully.

Heterogeneous organ models.

A theoretical study is made of three organ flow models with heterogeneity of capillary transit times. A new parametrization of Rose and Goresky's Model III facilitates in many cases a reduction to Goresky's Model II, accomplished by a special time shift. The shift parameter\(\tau _{c_z } = \tau _{c_m } - t_{APP} /b\) defined here is critical in this analysis of Model III. A new expression of the series for outflow concentration in Model III is given and proves useful in examining the model as an operator and in relating it to Models I and II. A result on parameter optimization is given: if\(\tau _{c_z } \geqslant 0\) then Model III cannot fit better than Model II. This is applied to some data from Rose and Goresky [Circulation Res.39, 541–544 (1976)] and raises a new question about their model. A heart model of Levin and Bassingthwaighte based on regional flow measurement is shown to be a discretized generalization of Model II.

Estudio hemodinamico de la estenosis y oclusion de la arteria carotida interna: valor de la combinación de la medida de flujo regionam cerebral y volumen sanguíneo mediante isótopos

Estudio hemodinamico de la estenosis y oclusion de la arteria carotida interna: valor de la combinación de la medida de flujo regionam cerebral y volumen sanguíneo mediante isótopos

Heterogeneous organ models

A theoretical study is made of three organ flow models with heterogeneity of capillary transit times. A new parametrization of Rose and Goresky's Model III facilitates in many cases a reduction to Goresky's Model II, accomplished by a special time shift. The shift parameterτ c z = τ c m − t APP/ b defined here is critical in this analysis of Model III. A new expression of the series for outflow concentration in Model III is given and proves useful in examining the model as an operator and in relating it to Models I and II. A result on parameter optimization is given: ifτ c z ≥0then Model III cannot fit better than Model II. This is applied to some data from Rose and Goresky [ Circulation Res. 39, 541–544 (1976)] and raises a new question about their model. A heart model of Levin and Bassingthwaighte based on regional flow measurement is shown to be a discretized generalization of Model II.

Correlations between cerebral grey matter flow and hepatic histology in alcoholism.

Thirty alcoholic with a mean age of 44.8 years were examined with the intravenous 133-Xenon method for measurements of regional cerebral flow (rCBF). The results were related to liver histology and hepatic function tests. While there exists no correlation between the rCBF values and hepatic function tests, an important connection between rCBF decrease and the severity of the histological liver analysis is shown. It is suggested that the hepatic biopsy is a good criterion for the long-term evaluation of alcohol impact upon the brain of a given individual and some physiopathological mechanism are discussed.

A simplified method of xenon-enhanced CT for regional cerebral blood flow (rCBF) measurement with reference to clinical experiences.

We introduced a simplified method of xenon-enhanced CT (SXe-CT) for obtaining the topographic regional cerebral blood flow (rCBF) map. In the SXe-CT, we used the method of brief (three to four minutes) inhalation of 40% xenon. To shorten the period of xenon inhalation, we substituted a predetermined brain-blood partition coefficient (L) in the entire brain for the directly estimated L to calculate the rCBF value. Because of its non-invasiveness and simplicity, the SXe-CT can be applied to the patients with diseases in the central nervous system (CNS) without any difficulties. During the past three years, we performed the SXe-CT on 150 occasions in 100 subjects, including those with moyamoya disease, other ischemic cerebrovascular diseases, arteriovenous malformations and normal pressure hydrocephalus. In this paper, the rCBF values of seven normal healthy adults with a mean age of 24 years are reported and the flow maps of some cases of CNS diseases are presented. The normal mean value of the hemispheres was 53, those of the gray matter were in the range of 38 to 72, those of the white matter were in the range of 26 to 35 and those of the basal ganglia and thalamus were 55 to 88 (values are given in ml/100 g/min). The SXe-CT has potential advantages in obtaining clinically useful rCBF measurements.

Reflex regional vascular responses during passive gastric distension in cats.

The increase in systemic vascular resistance during gastric distension in cats may result from variable vasomotor responses in several parallel regional vascular beds. Accordingly, in 23 anesthetized cats the stomach was passively distended with a balloon while systemic hemo-dynamics were monitored. Regional vascular responses were determined during control periods and during gastric distension either by injection of radioactive microspheres (15 cats) or by constant perfusion of vascularly isolated organs (8 cats). During distension, mean arterial pressure and systemic vascular resistance increased by 32 and 28%, respectively. Regional flow measurements indicated no significant alterations in any of the organs examined. Calculated regional vascular resistances indicated vasoconstriction in the kidneys (53%), small intestine (31%), and large intestine (37%) that was reversed by alpha-adrenergic blockade with phentolamine. Constant-flow perfusion studies confirmed the regional vasoconstriction in the renal, superior mesenteric, and hindlimb circulations. These studies suggest a regional heterogeneity of vasomotor response during passive gastric distension in cats that includes no change in vascular resistance in some organs and alpha-adrenergic vasoconstriction in others.

Regional myocardial perfusion measured by the avalanche radiation probe during cardiopulmonary bypass: Pharmacologic and physiologic alterations

Ronald P. Karlsberg, John Eugene, Kenneth P. Lyons, William E. Shell, and Vincent L. Gelezunas. Los Angeles and Long Beach, Calif. The health and function of myocardium is critically dependent on myocardial perfusion. However, cur- rent techniques for measurement of tissue perfusion are limited. More attention has focused on large- vessel blood flow or coronary anatomy, which pro- vides only indirect indications of perfusion to the myocardium. Investigation of the microcirculation in vivo has been hampered, in part, by the inability to obtain convenient, reliable measures of regional perfusion. In order to obtain repetitive in vivo measurement of regional microcirculation, we used the avalanche radiation probe to measure the clearance of intracor- onary xenon-133, a function of capillary flow. We have previously demonstrated the use of the ava- lanche radiation probe for determination of myocar- dial perfusion by detection of xenon-133 washout in a limited setting.’ Measurements of regional blood flow in detection volumes of 0.5 cm3 correlate closely to measurements of regional flow obtained by radio- active microspheres.’ Nevertheless, some variation from animal to animal and within animals was observed. Some of this variation was possibly because of the instability of the animal model and the inability to precisely stabilize and regulate regional perfusion. These factors include coronary blood flow and myocardial oxygen consumption. In order to perform further reliability and validity studies in a model in which the factors which control regional perfusion are more closely controlled, we validated measurements of regional perfusion

Effect of hypoxic-hypocapnia on cerebral regional oxygen consumption and supply

The effect of hypoxic-hypocapnia ( P aO 2, 35 mm Hg, P aCO 2, 22 mm Hg) on regional cerebral O 2 consumption and supply was determined in 18 α-chloralose-anesthetized open-chest adult cats. Regional arterial and venous O 2 saturation measurements determined by a microspectrophotometric technique were combined with regional flow measurements by the radioactive microsphere method to calculate cerebral regional O 2 consumption. In a control group, after blood flow was determined with 15 ± 3-μm-diameter microspheres, the heads were quick-frozen and measurements of flow and arterial-venous O 2 differences were obtained from nine brain regions. In the experimental group, similar measurements were obtained after the induction of hypoxic-hypocapnia. Cerebral blood flow was significantly lower than the control group during hypocapnia. Cerebral blood flow increased with the induction of hypoxia. Arterial and venous O 2 saturation decreased uniformly and to the same extent in the nine examined brain regions. This maintained the arterial-venous O 2 saturation difference. O 2 extraction and consumption were unaffected. The brain O 2 supply/consumption ratio was maintained during hypoxic-hypocapnia indicating adequate and uniform protection in this condition throughout the brain.

Measurements of coronary blood flow and degree of stenosis: Current clinical implications and continuing uncertainties

Initial measurements of coronary blood flow in human beings were limited by methodologic inadequacies causing clinically important areas of reduced perfusion to be incompletely represented or overlooked. More recent measurements have provided insight into clinically relevant pathophysiology. There has been increasing appreciation of the need for values of flow to be related to concomitant myocardial oxygen demand, and of the importance of evaluating perfusion in relation to coronary vascular reserve. Regional flow measurement techniques have progressed significantly during the past decade and have provided better insight into perfusion deficits in ischemic heart disease. A greatly improved understanding of the relation between the arteriographic degree of stenosis and perfusion limitation also has developed, in reviewing studies addressing these points, the present article attempts to highlight their current clinical implications and address continuing uncertainties meriting further attention.

Cerebral blood flow studies in man using recirculation corrected height/area (H/A) computations for intravenous injection of 133Xenon.

Our height/area (recirculation-corrected) non-invasive cerebral blood flow method compares well with k1 values and k average as determined from k1, k2, p1 and p2 by Obrist computations. The height/area method provides regional flow measurements with less variability than k1 due to low regional head counts, head motion and end-tidal gas sample variations. Derivation of the mathematical model is for a single flow compartment and suited for tomographic measurements such as PET. Collimated detector data using our computation provides a good approximation of flow even for multiple compartments. Our approach permits a lower counting rate by either a smaller isotope dose or better detector collimation than multicompartment curve fitting methods.

Changes in regional myocardial blood flow and variable development of hypertrophy after aortic banding in puppies.

Supravalvar aortic banding was performed in 6 to 12 week puppies. Sixteen animals were studied 7.3 (3.5 to 10) months later, closed-chested under morphine-chloralose, catheters being positioned in the great vessels and heart, including the left atrium for microsphere injection. Compared with 11 controls, eight dogs developed biventricular hypertrophy, four isolated left ventricular hypertrophy and four had no hypertrophy. The left ventricular systolic pressure was similar (P greater than 0.05) in these 3 banded groups (mean, 30 +/- 2 [SEM] kPa, [222 +/- 16 mmHg], n = 16). The left ventricle was divided into three coronal slices with approximately 59 samples being taken from subendocardial, midwall, and subepicardial layers and additional samples from the atria and right ventricle for regional myocardial flow measurement. As left ventricular hypertrophy increased, the subendocardial/subepicardial flow ratio decreased (r = -0.8). Heterogeneity of left ventricular regional myocardial flow, including a base-to-apex decrease in flow, present in controls, was markedly reduced in the banded dogs. Analysis of variance was found to be the most sensitive test for detecting left ventricular perfusion abnormalities since in banded dogs without hypertrophy, total and regional subendocardial/subepicardial flow ratios were not significantly different from control values, whereas the subendocardial circumferential flow pattern determined by analysis of variance was significantly different from control in these dogs (P less than 0.05).

Radiogeological Assessment of Candidate Sites For Nuclear Waste Repositories, Exemplified by Studies of The Stripa Pluton, Sweden

ABSTRACTInvestigation of candidate sites for nuclear waste isolation will require an assessment of their radiogeologic settings. Studies at the Stripa research facility in granitic rock of central Sweden incorporated the distribution and abundance of naturally occurring radioelements in rocks encompassing the underground experiments and in the accompanying fracture-controlled groundwater system. These studies showed that besides defining the natural radioactivity baseline upon which the effects of radioactive waste will be superimposed, radioelement distributions can be used to determine the apparent age of the groundwater and its flow paths. In crystalline rocks, where the groundwater systems are confined to the joints and fractures, the uranium daughter element, radon-222 in the water serves as a natural tracer to locate fractures along which significant flow is occurring and to measure the flow rates. The heat production from radioactive decay of uranium-238, thorium-232 and potassium-40 in the rock, combined with measurements of regional and local geothermal heat flow, permit calculation of the apparent size of the rock mass that will encompass the repository. This method is especially useful in terranes such as at Stripa where the contacts between plutons and older rocks are concealed.