Heterogeneity Of Myocardial Blood Flow Research Articles

Pharmacologic stress-induced regional myocardial blood flow heterogeneity and left ventricular wall thickening abnormality: Comparison of intravenous adenosine with dipyridamole in a model of critical coronary stenosis

Variations in reported sensitivity of myocardial perfusion scans or wall motion abnormalities during pharmacologic stress with intravenous adenosine and dipyridamole may be caused by differences in myocardial oxygen demand or myocardial blood flow redistribution induced by each agent. To investigate the physiologic correlates of functional abnormalities during pharmacologic stress testing, regional myocardial blood flow (radiolabeled microsphere technique) and left ventricular segmental wall thickening (quantitative two-dimensional echocardiography) were measured in 9 dogs with an open chest model of critical stenosis of the left circumflex coronary artery. Data were obtained at baseline and peak drug infusion for intravenous adenosine (0.42 mg/kg over a 3-minute period) and for intravenous dipyridamole (0.56 mg/kg over a 4-minute period). Adenosine and dipyridamole induced regional flow abnormality in 7 (77%) of 9 dogs. Myocardial segments with decreased endocardial/epicardial flow ratio were similar for both agents (2.9 ± 1.8 vs 2.7 ± 1.3, p = [NS]). Segments with myocardial flow heterogeneity (ratio of endocardial flow to control left anterior descending/left circumflex endocardial flow) were similar for both agents (2.7 ± 0.9 vs 2.3 ± 1.0, p = NS). Adenosine-induced wall thickening abnormality (77% vs 55% with dipyridamole) correlated with regional flow abnormality. Significantly lower mean arterial pressure (53 ± 1.7 mm Hg vs 64 ± 1.9 mm Hg, p < 0.01) and more prolonged drug effect (18 ± 6.4 min vs 3 ± 1.4 min, p < 0.001) were seen for dipyridamole compared with adenosine. Adenosine induces regional flow abnormality similar to dipyridamole but with less hemodynamic perturbation, and adenosine-induced wall thickening abnormality more closely parallels regional flow abnormality. (Am Heart J 1997;133:78-86.)

Physiologic and clinical significance of myocardial blood flow quantitation: what is expected from these measurements in the clinical ward and in the physiology laboratory?

In this essay we review data on absolute quantitation of myocardial blood flow (MBF) in humans. Earlier work established that coronary heart disease (CAD) can be detected by coronary angiography and that this disease has characteristic features at rest and during stress, which indicate the linkage between regional metabolic needs and myocardial perfusion. In the 1970s myocardial perfusion was mapped in patients with radioxenon, but this method had significant technical limitations. About the same time, radioactive microspheres were introduced for cardiovascular research and investigations; these particles provided insights on MBF in acute infarction and ischemia, myocardial reperfusion, collateral circulation, myocardial blood flow during exercise, coronary flow reserve (CFR), and layer-to-layer distribution of MBF. Studies with microspheres also permitted investigators to establish the presence in the heart of MBF heterogeneity. Currently, there are several techniques that aim at extending these concepts into clinical investigation. Two of these techniques, i.e. Doppler coronary flow velocity and fast magnetic resonance imaging assess epicardial flow dynamics and CFR. Contrast myocardial echocardiography is another novel technique which has been useful in mapping the area at risk, reperfusion, myocardial viability and collateral circulation. This essay also considers the emerging technique of intracoronary ultrasound which has shown evidence of disease underestimation by conventional contrast angiography. Positron emission tomography (PET) is a noninvasive technique that uniquely and quantitatively maps myocardial perfusion and CFR. The latter can be computed before and after angioplasty. PET studies have further demonstrated that chronic myocardial ischemia does not exist as a distinct state in patients with CAD. From the above investigations the concept has arisen that not only is CAD an entity involving epicardial vessels but also, in a significant portion of patients, an abnormal microcirculation plays an important role in the pathogenesis of ischemic syndromes. PET studies have relatively low spatial resolution since they cannot resolve layer-to-layer absolute MBF.

Microheterogeneity of myocardial blood flow in rabbit hearts during normoxic and hypoxic states.

The goal of this study was to evaluate microheterogeneity of myocardial blood flow and its dependence on arterial O2 tension (PaO2). We measured within-layer distribution of regional blood flows in the left ventricles of anesthetized rabbits in both normoxic and hypoxic states with myocardial region sizes in the range of 0.01-1.0 mm2. A novel method of digital radiography combined with the technique of 3H-labeled desmethylimipramine deposition enabled us to visualize and accurately quantitate regional blood flow at such high levels of resolution. To analyze myocardial blood flow patterns, we computed the coefficient of variation (CV) and the correlation between adjacent regional flows (CA). The CA values were larger in the hypoxic state (PaO2 = 26 +/- 5 mmHg) than in the normoxic state (PaO2 = 97 +/- 20 mmHg) at all levels of resolution (P < 0.001). In the normoxic state, there was a transmural difference in CA (P < 0.001); CA increased with depth of the left ventricle (from subepicardium to subendocardium). However, the relation between CA and the depth of the left ventricle was not statistically significant in the hypoxic state. The CV values were smaller in the hypoxic state than in the normoxic state at all levels of resolution (P < 0.001). When the degree of resolution was reduced from 0.01 to 1.0 mm2, CV decreased by 75% in the normoxic and by 69% in the hypoxic state. Thus we conclude that 1) the decrease in PaO2 increases similarity of blood flows in nearby regions and decreases myocardial blood flow heterogeneity, and 2) similarity of regional blood flows increases with depth of the left ventricle in the normoxic state, but this transmural difference disappears in the hypoxic state.

Blood flow distribution in necrotic versus nonnecrotic rabbit hearts.

The spatial myocardial blood flow heterogeneity of the normal heart was previously investigated by means of the standard microsphere-defined regional myocardial blood flow in nonischemic hearts. We determined the probability density functions of coronary blood flows in the rabbit heart at selected macroautoradiographic 20-microns cross-sections of the left ventricle in nonischemic as well as infarcted hearts. Macroautoradiography gave us spatial resolutions of 0.1-0.2 mm. As a tracer we used 14C-iodoantipyrine given into the root of the aorta. We report here for the first time a systematic study of the shape of the flow probability density functions during acute regional myocardial necrosis. As the hearts became progressively and extensively necrotic, the distribution of flows changed its characteristics showing two independent components. The first component was the peak representing the nonischemic regions in the hearts subjected to acute ischemia. The second component was a monotonically decreasing component associated with very low flows and necrosis in the severely hypoperfused portion of the hearts. This monotonically decreasing component became larger as the extent of ischemia increased and was well separated from the peak attributable to the nonischemic regions. We could not demonstrate a leftward shift of the nonischemic central peak in the ischemic hearts. Our research shows that in transaxial radionuclide cardiac sections, such as those that might be obtained and analyzed in clinical SPECT and clinical PET, variable amounts of myocardial necrosis will result in a composite curve of myocardial blood flow heterogeneities. One portion of the curve will indicate the distribution of flows in the nonischemic zones. The other portion will vary in magnitude with the extent of ischemia, exhibit the shape of monotonically decreasing curve. Depending upon the spatial resolution of the radionuclide imaging technique utilized, a border zone will exist representing the interface between normally perfused and occluded vascular beds. In our investigation, it was found that the border zone determined statistically was consistently and significantly smaller than the border zone determined visually.

Heterogeneity of myocardial blood flow.

Myocardial blood flow is heterogeneous, whether considered by chamber, by layers of the ventricular walls, or by microregions within layers. There is also variability of myocardial flow reserve, particularly in layers and microregions, even when the heart is arrested. The variability of flow during arrest may be associated with the resistance pathways to each region, but the variability of flows in the beating heart with vascular tone is probably due to regional differences in work and thus oxygen demand. Heterogeneity by layer may be responsible for the subendocardial ischemia that is common to many forms of heart disease. Microheterogeneity may account for the patchy necrosis that occurs with chronic ischemia.

Local Mitochondrial Enzyme Activity Correlates with Myocardial Blood Flow at Basal Workloads

To study whether heterogeneous myocardial blood flow relates to the local oxidative capacity of cardiac muscle, local blood flow at resting cardiac workloads and the activity of the mitochondrial enzyme succinate dehydrogenase (SDH) were determined in small regions of the left ventricle of seven anaesthetized, mechanically ventilated, open-chest pigs (25-35 kg). Following injection of radioactive microspheres (15 μm Ø) into the left atrium, the heart was rapidly excised and cut into five transverse slices, which were simultaneously freeze-clamped between two aluminum blocks precooled at -80°C. The left ventricle was then subdivided into 84 samples of about 0.9 g. Myocardial blood flow was 0.88 ± 0.34 ml/min/g wet weight (ww), and SDH activity 1.46 ± 0.33 μmol/min/g ww (mean ± S.D., n = 7). Local data were normalized to their respective mean values in each pig, and then pooled. Local blood flow ranged from 0.32 to 1.63 of the mean, and blood flow heterogeneity characterized by the coefficient of variation (CV=S.D./mean) was 18.4%. Normalized local SDH activity ranged from 0.16 to 1.94, with a CV of 21.8%, significantly exceeding measurement error (CV=4.5%). Local blood flows and SDH activities did not vary among transmural sublayers of the left ventricle, but variation within each sublayer was considerable. In six of the seven pigs, local blood flow correlated (P < 0.05) with SDH activity, with correlation coefficient (r) ranging from 0.26 to 0.54 (for pooled data: r=0.27, P < 0.0001). When expressed per gram dry weight, heterogeneity of SDH activity increased (P < 0.05), and here also local blood flow correlated with SDH activity in all pigs (for pooled data: r=0.45, P < 0.001). Hence, heterogeneity of mitochondrial capacity within cardiac muscle partly explains the heterogeneity of myocardial blood flow, even though myocardial perfusion at rest was studied in relation with a maximal enzyme rate. The low correlation coefficient clearly indicates that at resting workloads other factors also play a role.

Dobutamine thallium-201 tomography for evaluating patients with suspected coronary artery disease unable to undergo exercise or vasodilator pharmacologic stress testing

Objectives. The aim of this study was to assess the feasibility, safety and diagnostic accuracy of a high dose dobutamine infusion in conjunction with thallium-201 single-photon emission computed tomography in 144 patients (72 men and 72 women with a mean age of 65 ± 10 years) unable to perform exercise or pharmacologic vasodilator stress testing.Background. Dobutamine increases myocardial oxygen consumption by increasing heart rate, contractility and arterial blood pressure. In addition, it causes myocardial blood flow heterogeneity and thus may be a useful stress for noninvasive detection of coronary artery disease.Methods. Dobutamine was administered intravenously at incremental doses of 5, 10, 20, 30 and up to 40 μg/kg per min at 3-min intervals. After 1 min of the maximal dose, 3 mCi of thallium-201 was injected and the infusion was continued for an additional 2 min. Thallium-201 tomography was performed 5 to 10 min after termination of the infusion and 4 h later. The images were visually assessed for the presence and vascular location of perfusion defects and the extent of thallium redistribution. Coronary angiography was performed in 84 patients, with a >50% stenosis considered significant.Results. Dobutamine significantly (p = 0.0001) increased the heart rate (from 75 ± 14 beats/min to 120 ± 23 beats/min), systolic blood pressure (from 136 ± 23 mm Hg to 148 ± 35 mm Hg) and the rate-pressure product (from 10,144 ± 2,517 to 17,858 ± 4,349) from baseline to peak infusion rate, respectively. Most patients (75%) experienced side effects during the infusion, but 74% tolerated a dobutamine dose of 40 μg/kg per min and 97% a dose of 30 μg/kg per min. The more common side effects were typical (26%) and atypical (5%) chest pain, palpitation (29%), flushing (14%), headache (14%) and dyspnea (14%). The overall sensitivity of dobutamine tomography was 86% in the patients who underwent coronary angiography and 84% in those with single-vessel, 82% in those with double-vessel and 100% in those with triple-vessel disease. Seventy-eight percent of vessels with severe (≥70%) stenoses were identified with dobutamine tomography. The specificity of dobutamine tomography was 90% for patients and 86% for individual vessels.Conclusions. A high dose dobutamine infusion in conjunction with thallium tomography appears to be a well tolerated and accurate method for diagnosing coronary artery disease in patients unable to perform exercise or vasodilator pharmacologic stress testing.

Adenosine myocardial perfusion imaging in the noninvasive diagnosis and prognosis of coronary artery disease

AbstractAdenosine is a purine base compound which is of fundamental importance in many physiologic processes in the body, including vasodilation in most arterial vascular beds. Adenosine produces maximal or near‐maximal coronary vasodilation by interacting with the adenosine A2 receptors in the cell wall, on a dose dependent fashion. The mechanism of thallium‐201 myocardial perfusion defects induced by adenosine scintigraphy is a heterogeneity of myocardial blood flow due to a greater coronary flow increase in the normal arteries and a lesser increase in the stenotic arteries. The ultra‐short half‐life of adenosine (&lt; 10 sec) necessitates continuous intravenous administration at a dose of 140 μg/kg/min for six min. The excellent safety record of this regimen has been demonstrated in several thousand patients in the United States. Side effects occur in most patients during adenosine infusion. Chest pain occurs often and in some cases may be due to a true coronary steal phenomenon. In the author's experience, first degree AV block occurs in approximately 10% and second or third degree AV block in approximately 4% of the patients, and are due to the negative dromotropic effect of adenosine on the AV node. On the positive side, these untoward effects are very short‐lived and typically disappear within one or two minutes after discontinuing the adenosine infusion. No serious complications or fatalities have been observed to date with this test. The cumulative experience with adenosine thallium‐201 scintigraphy indicates high sensitivity and specificity in the diagnosis of coronary artery disease. Recent data also suggest it may be an excellent technique to assess a patient's prognosis early after a myocardial infarction. Adenosine‐induced coronary vasodilation, in combination with thallium‐201 or the new technetium‐99m perfusion agents, holds great promise in the assessment of patients with coronary artery disease. © 1993 Wiley‐Liss, Inc.

Heterogeneity of myocardial blood flow under normal conditions and its dependence on arterial PO2

We studied the heterogeneity of myocardial blood flow in nine anesthetized closed-chest dogs using an indicator-dilution technique that allows the stochastic description of transport characteristics for three inert gases (helium, argon, and xenon) from the coronary inflow to outflow. The results show that under normal conditions the transcoronary transport of the tracers is spatially heterogeneous. Heterogeneity is strongly dependent on the arterial oxygen tension over a range of 40-200 Torr. This could be similarly observed with each tracer gas despite different physicochemical properties and was largely independent from the magnitude of coronary blood flow. The results are interpreted to mean that the arteriolar or intratissue PO2 influences myocardial blood flow over a broad range and possibly acts as an important integrating factor in the local regulation of coronary blood flow and flow reserve.

Fractal nature of regional myocardial blood flow heterogeneity.

Spatial variation in regional flows within the heart, skeletal muscle, and in other organs, and temporal variations in local arteriolar velocities and flows is measurable even with low resolution techniques. A problem in the assessment of the importance of such variations has been that the observed variance increases with increasing spatial or temporal resolution in the measurements. This resolution-dependent variance is now shown to be described by the fractal dimension, D. For example, the relative dispersion (RD = SD/mean) of the spatial distribution of flows for a given spatial resolution, is given by: RD(m) = RD(mref).[m/mref]1-Ds where m is the mass of the pieces of tissue in grams, and the reference level of dispersion, RD(mref), is taken arbitrarily to be the RD found using pieces of mass mref, which is chosen to be 1 g. Thus, the variation in regional flow within an organ can be described with two parameters, RD(mref) and the slope of the logarithmic relationship defined by the spatial fractal dimension Ds. In the heart, this relation has been found to hold over a wide range of piece sizes, the fractal Ds being about 1.2 and the correlation coefficient 0.99. A Ds of 1.2 suggests moderately strong correlation between local flows; a Ds = 1.0 indicates uniform flow and a Ds = 1.5 indicates complete randomness.

Nonuniformity of the transmural distribution of coronary blood flow during the cardiac cycle. In vivo documentation by contrast echocardiography.

This study was performed to examine the transmural (endocardial vs. epicardial) heterogeneity of myocardial blood flow during the cardiac cycle (systole vs. diastole). Twenty-four contrast echocardiographic injections were performed in seven open-chest anesthetized dogs either into left anterior descending or circumflex coronary artery or into the aortic root. Two-dimensional echocardiography in short-axis view was performed and was digitized off-line into a 256 x 256 pixel matrix with 256 gray levels/pixel. All end-diastolic and end-systolic frames before and to peak contrast were analyzed. A region of interest corresponding to the most intensely opacified myocardial segment was traced, the mean videodensity measured, and the frame of initial contrast appearance detected. The region of interest was divided into three equal parallel layers corresponding to the endocardial, midcardial, and epicardial myocardium. When the echocardiographic contrast effect initially appeared in diastole, the increment in videodensity was greater for the endocardium (131 +/- 48%) than for the epicardium (71 +/- 37% of the increment in videodensity of the entire wall) (p less than 0.05). This inhomogeneity subsequently disappeared in the following end-systolic frame. When the initial echocardiographic contrast effect appeared in systole, intensity was higher in epicardium (136 +/- 83%) than in endocardium (60 +/- 60%) (p less than 0.05). However, in the following diastole, intensity was not significantly different for the two layers. Thus, myocardial contrast echocardiography demonstrates that coronary blood flow is primarily subendocardial in distribution during diastole and subepicardial during systole.

Spatial heterogeneity of local blood flow and metabolite content in dog hearts

Spatial variation (heterogeneity) of myocardial blood flow was studied under basal conditions in relation to four biochemical markers: creatine kinase (CK), lactate dehydrogenase (LDH), ATP, and glycogen. A total of 508 individual 0.5-g samples from the left ventricular free wall was studied in 12 dogs. Myocardial blood flow was measured by radioactive microspheres (15 micron diam) injected via a pigtail catheter into the left ventricle during light sedation (closed-chest flow measurements); following thoracotomy, a second set of microspheres was injected via a catheter into the left atrium (open-chest flow measurements, n = 5). In 27-54 samples/heart, myocardial blood flow, CK, LDH, protein, ATP, and glycogen were determined, permitting a direct correspondence between local blood flow and metabolic markers in each sample and an assessment of the spatial heterogeneity of flow and metabolite content. Correlations between myocardial blood flow per gram tissue and metabolite concentration per gram tissue in pooled data were weak but significant: partial correlation coefficients were 0.137 for CK (P = 0.024), 0.167 for LDH (P = 0.006), 0.341 for ATP (P less than 0.001), 0.123 for glycogen (P = 0.053), but not significant for protein vs. myocardial blood flow. The coefficient of variation, which defines the extent of spatial heterogeneity, averaged 20% for closed-chest flow measurements, 19% for open-chest flow measurements, 22% for CK, 17% for LDH, 15% for protein, 8% for ATP, and 18% for glycogen; these values are over and above the variability due to the technique error, indicating a definite physiological spatial variability. The correlation between local blood flow and the studied metabolites can only explain a minor portion of the spatial heterogeneity of myocardial blood flow. Although a physiological link between blood flow and metabolite content for small regions of the heart is demonstrated, the true local variability of blood flow may be modulated predominantly by other factors.

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.

Dependence of spatial heterogeneity of myocardial blood flow on mean blood flow rate in the rabbit heart.

The relationship between spatial heterogeneity of myocardial blood flow and the rate of perfusion was examined in anaesthetised-chest rabbits. Blood flow determinations employed the radioactive microsphere technique. Five tissue samples were obtained from each of four regions of the left ventricle: left septum, right septum, subendocardium and subepicardium. Standard deviation (SD) and the coefficient of variation (CV = SD/mean flow x 100), an index of spatial heterogeneity, were computed. A wide range of mean coronary flows was obtained in seven groups by inspiration of room air, 8% O2, 8% O2 and 10% CO2, 100% O2, 100% O2 and hyperventilation, and by administration of adenosine or chromomar HCl. Significant differences in CV were found between treatment groups at the upper and lower ends of the flow range. A significant positive linear correlation between overall SD and mean coronary flow was found (r = 0.760). A significant inverse linear relationship between CV and mean flow was found over the entire range of flows studied (r = -0.482). An improved correlation between CV of calculated coronary vascular resistance and mean vascular resistance (r = 0.742) amongst these treatments suggests that spatial heterogeneity is better described by the variability in calibre of large arterioles. This decreased heterogeneity accompanying high flows or reduced vascular resistance may be beneficial in terms of O2 supply and demand under conditions of myocardial stress.

Spatial and temporal heterogeneity of left ventricular perfusion in awake dogs

Summary The purpose of this investigation was to ascertain if spatial and temporal heterogeneity of myocardial blood flow occurred in awake dogs under basal conditions. Myocardial perfusion was assessed by injecting differently labeled 15±5 μ or 7 to 10 μ microspheres into the left atrium. Spatial heterogeneity of perfusion was determined in 24 awake dogs by analyzing the distribution of perfusion to 96 segments of the left ventricle. Spatial heterogeneity expressed as the relative dispersion of the segmental perfusion averaged 21.4±SE 1.5 per cent. The variation in segmental perfusion due to the microsphere technique was assessed by injecting three or four batches of microspheres simultaneously in six of the dogs. Temporal heterogeneity was assessed by sequentially injecting three or four batches of microspheres, at 1 minute intervals, in six other dogs while left atrial pressure, arterial pressure, heart rate, and left ventricular perfusion were held constant. The average range of segmental perfusion was greater in the sequentially injected dogs than in the simultaneously injected dogs (26.0±SE 2.7 per cent vs 16.3±SE 1.7 per cent, respectively [p

Temporal heterogeneity of myocardial blood flow in anesthetized dogs.

Temporal variation in perfusion to small segments of the myocardium was studied in 19 opened-chest dogs. In six control dogs, three or four differently labeled 7-10 mu microspheres were injected simultaneously into the left atrium to assess the variability in measured myocardial perfusion due to the microsphere technique. In 13 other dogs, microspheres were injected four times at 5 minute intervals while various hemodynamics parameters (mean aortic pressure, peak systolic pressure, heart rate, left ventricular end-diastolic pressure, and Vmax) were stable (less than 10% variation in any one parameter). The left ventricles were divided into 96 segments, the mean weight+/- SD of each segment was 0.95+/-0.17 grams. The flow to each segment was expressed as a percent of the mean flow of the three or four measured flows to that segment, and the difference between the largest and the smallest percent of each segment was taken as a measure of the variability of flow to that segment. The average variability of segmental flow (mean +/-SD) when the three to four differently labeled microspheres were injected was 14.0+/-4.7; and the variability when differently labeled microspheres injected sequentially was 31.0+/-10.8% (P less than 0.001). Furthermore, in the sequentially injected animals the magnitude of temporal variation was similar in various subdivisions of the ventricle (layers, walls, apex to base). The mean and standard deviation of the variability of flow to the endo, mid, and epicardial layers were 28.7+/-10.2, 30.0+/-11.3 and 34.5+/-12.4%, respectively. These changes may reflect either spontaneous or local autoregulatory changes in precapillary sphincters or arterioles.

Redistribution of blood flow during sustained high skin temperature in resting man.

Redistribution of blood flow during sustained high skin temperature in resting man.

Normal distribution of cardiac output in the unanesthetized, restrined rhesus monkey.

ARTICLESNormal distribution of cardiac output in the unanesthetized, restrined rhesus monkeyR. P. Forsyth, A. S. Nies, F. Wyler, J. Neutze, and K. L. MelmonR. P. Forsyth, A. S. Nies, F. Wyler, J. Neutze, and K. L. MelmonPublished Online:01 Dec 1968https://doi.org/10.1152/jappl.1968.25.6.736MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByAnatomy of rodent and human livers: What are the differences?Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, Vol. 1865, No. 5The history of proximal carotid protection and flow reversal to prevent stent angioplasty embolizationSeminars in Vascular Surgery, Vol. 31, No. 1Measurement of blood flow in the skin and oral mucosa of the rhesus monkey (Macaca mulatta) using laser doppler flowmetryComparative Biochemistry and Physiology Part A: Physiology, Vol. 106, No. 1A Physiologically Based Pharmacokinetic Model for Chloropentafluorobenzene in Primates To Be Used in the Evaluation of Protective Equipment Against Toxic GASES1 July 2016 | Toxicology and Industrial Health, 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