Biomedical subjects

R D Okada

Publications and source records attributed to R D Okada.

At least 91 records · Page 5Linked to original sources

PubMed1985

The relationship between proton nuclear magnetic resonance relaxation parameters and myocardial perfusion with acute coronary arterial occlusion and reperfusion.

Previous investigators have demonstrated that acute myocardial ischemia, whether followed by reperfusion or not, is associated with prolongation of the proton nuclear magnetic resonance (NMR) relaxation times T1 and T2. Heretofore, the relationship between the severity of ischemia and alterations of these relaxation times has not been assessed. In our studies, changes in T1 and T2 were compared with myocardial perfusion in dogs both before and during 30 and 60 min of coronary arterial occlusion. In addition, studies were performed to assess the impact of reperfusion on relaxation times after 30 and 60 min of coronary occlusion. In the reperfusion studies the relationship between myocardial relaxation times and flow during the preocclusion, occlusion, and the 15 min reperfusion periods were studied. In the occlusion-only preparations, there was a significant inverse relationship between the relaxation times and flow during occlusion. In the reperfusion preparations there was a significant direct relationship between T1 and T2 and flow during the period of reperfusion. There was no significant relationship between the relaxation times and flow during occlusion in groups that subsequently underwent reperfusion, and no relationship between T1 and T2 and preocclusion flow in either the occlusion-only or reperfusion groups. These data suggest that the proton relaxation times provide an indication of the severity of an ischemic insult. Since NMR images can be generated that are sensitive to differences in these relaxation parameters, NMR imaging may provide a means to assess noninvasively the severity of the myocardial ischemic insult.

Acute Disease↗

PubMed1985

Left ventricular function before and after reaching the anaerobic threshold.

Simultaneous pulmonary gas exchange analysis and exercise radionuclide angiography were performed in 24 normal patients (14 supine and ten upright). Left ventricular (LV) volumes and ejection fraction (EF) were measured at rest, anaerobic threshold (point of nonlinear increase in ventilation relative to oxygen uptake), and peak exercise. The anaerobic threshold occurred at a similar heart rate for supine vs upright exercise, 78 percent and 77 percent of peak heart rate, respectively. The anaerobic threshold occurred at a similar workload for supine vs upright exercise, 60 percent and 56 percent of peak workload, respectively. The anaerobic threshold also occurred at a similar oxygen uptake for supine vs upright exercise, 69 percent vs 69 percent of peak oxygen uptake, respectively. For both exercise modes, mean LVEF increased (p less than 0.01) by a similar amount (.06 vs .07) from rest to anaerobic threshold, but there was no further increase from anaerobic threshold to peak exercise. The mechanism of the increase was a reduction in end-systolic volume with little or no change in end-diastolic volume. This increase was not seen in patients with rest LVEF in the high normal range (greater than 0.68). Therefore, for both supine and upright exercise, the major augmentation in LVEF occurs at earlier stages of exercise, prior to the anaerobic threshold. After the anaerobic threshold, the LVEF response may be highly variable, and a uniform increase is not necessarily expected even in normal subjects.

Adult↗

PubMed1985

Magnetic resonance imaging of the heart using image planes oriented to cardiac axes: experience with 100 cases.

Electrocardiographically gated magnetic resonance images were acquired in 100 patients with a variety of cardiac diagnoses in planes oriented to intrinsic axes of the heart and aorta. The technique used combines patient positioning and alteration of magnetic gradient angle. Images in these planes appear to have advantages over conventional orthogonal images, both for display of cardiovascular anatomy and for evaluation of cardiac size and function.

Adolescent↗

PubMed1985

Effect of a delay in commencing imaging on the ability to detect transient thallium defects.

Sixty patients, 42 with coronary disease and 18 normals, were studied to assess the impact of a delay following exercise in commencing thallium imaging on the sensitivity for detecting ischemic transient defects. Three sets of images were obtained beginning 2 min, 18 min, and 2 hr after exercise. Each patient's images were separated into two pairs of studies for analysis: 2 min-2 hr and 18 min-2 hr. Of the 42 patients with coronary disease, a greater number had transient defects detected on the 2 min-2 hr compared with the 18 min-2 hr study (22 compared with 14, p less than 0.05). False positives were not increased by earlier imaging. We conclude that a modest (18 min) delay obtaining the first set of images causes a significant reduction in the ability to detect transient thallium defects, and that imaging should begin several minutes after exercise.

Adult↗

PubMed1985

Cardiac magnetic resonance imaging: the Massachusetts General Hospital experience.

The combination of gated cardiac imaging with the magnetic resonance parameters of flow void and tissue characterization forms the basis for a powerful noninvasive technique for imaging the cardiovascular system. Images constructed in planes orthogonal to the axis of the heart allow cardiac structures to be reproducibly detected in serial studies and measured. The data acquisition techniques used at Massachusetts General Hospital are presented, along with examples of their application in a variety of cardiac diseases. Future prospects are illustrated with flow-encoded images and with surface coil techniques.

Aorta↗

PubMed1984

Quantification of pulmonary thallium-201 activity after upright exercise in normal persons: importance of peak heart rate and propranolol usage in defining normal values.

Fifty-nine normal patients (34 angiographically normal and 25 clinically normal by Bayesian analysis) underwent thallium-201 imaging after maximal upright exercise. Lung activity was quantitated relative to myocardial activity and a lung/myocardial activity ratio was determined for each patient. Stepwise regression analysis was then used to examine the influence of patient clinical characteristics and exercise variables on the lung/myocardium ratio. Peak heart rate during exercise and propranolol usage both showed significant negative regression coefficients (p less than 0.001). No other patient data showed a significant relation. Using the regression equation and the estimated variance, a 95% confidence level upper limit of normal could be determined for a give peak heart rate and propranolol status. Sixty-one other patients were studied to validate the predicted upper limits of normal based on this model. None of the 27 patients without coronary artery disease had an elevated lung/myocardial ratio, compared with 1 of 8 with 1-vessel disease (difference not significant), 6 of 14 with 2-vessel disease (p less than 0.005), and 6 of 12 with 3-vessel disease (p less than 0.0001). Thus, lung activity on upright exercise thallium-201 studies can be quantitated relative to myocardial activity, and is inversely related to peak heart rate and propranolol use. Use of a regression analysis allows determination of a 95% confidence upper limit of normal to be anticipated in an individual patient.

Adult↗

PubMed1984

Sources of variability in the radionuclide angiographic assessment of ejection fraction: a comparison of first-pass and gated equilibrium techniques.

Measurements of ejection fractions (EF) determined by first-pass and gated equilibrium radionuclide angiography are widely believed to be equivalent. To compare these measurements in a large group of patients over a wide range of EF values, left ventricular (LV) and right ventricular (RV) EFs at rest were measured in 135 consecutive patients who underwent the 2 methods of radionuclide angiography within 1 hour: first-pass upright with a multi-crystal camera in the anterior projection and gated equilibrium supine with a single-crystal camera in the left anterior oblique projection. The population included 18 normal patients and 117 patients with various cardiac and pulmonary disorders. First-pass and gated equilibrium LVEF correlated well (r = 0.83, p less than 0.001), but the slope of the regression line was different from unity, with the first-pass values lower than the gated equilibrium values (0.51 +/- 0.16 vs 0.56 +/- 0.15, p less than 0.05 [mean +/- standard deviation] ). Among the 45 patients with a gated equilibrium LVEF of less than or equal to 0.50, the correlation (r = 0.84) was better than that for the 90 patients with a LVEF greater than 0.50 (r = 0.44, p less than 0.05). However, in the latter group, the correlation remained good in the 15 patients with cardiomegaly due to aortic or mitral regurgitation (r = 0.80). Inter- and intraobserver error was similar for both methods. In contrast, there was a poor correlation between first-pass and gated equilibrium RVEF, with the first-pass values higher than the gated equilibrium values (0.51 +/- 0.11 vs 0.43 +/- 0.11, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

Significance of increased lung thallium-201 activity on serial cardiac images after dipyridamole treatment in coronary heart disease.

Increased lung thallium-201 (Tl-201) activity occurs in patients with severe coronary artery disease (CAD) on initial postexercise images. To determine the significance of assessing lung Tl-201 on serial imaging after dipyridamole therapy, initial and delayed (2 to 3 hours) Tl-201 imaging was performed in 40 patients with CAD and 26 normal control subjects. Lung Tl-201 activity was quantitated as a percentage of maximal myocardial activity for each imaging time (lung Tl-201 index). The mean initial lung Tl-201 activity was 42 +/- 2% (+/- standard error of the mean) in 26 control subjects, 56 +/- 2% in 25 patients with 2- or 3-vessel CAD (p less than 0.001) and 53 +/- 2% in 15 patients with 1-vessel CAD (p less than 0.005 compared with control subjects) (difference not significant between 1-vessel and multivessel CAD). Dipyridamole lung Tl-201 activity decreased relative to the myocardium from initial to delayed images (p less than 0.001) in patients with CAD but not in control subjects. When a dipyridamole lung Tl-201 index of 58% (mean +/- 2 standard deviations for control subjects) was chosen as the upper limit of normal, 14 of 40 of the CAD patients (35%) had abnormal values and all control patients had values within normal limits. These 14 patients with CAD and abnormal initial lung Tl-201 indexes had rest ejection fractions that were not significantly different from those in patients with CAD, and normal initial dipyridamole lung Tl-201 index (58 +/- 4% and 63 +/- 2%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

Serial thallium-201 imaging after dipyridamole for coronary disease detection: quantitative analysis using myocardial clearance.

After dipyridamole, canine studies have demonstrated a slower rate of myocardial thallium-201 clearance from zones distal to a coronary artery stenosis compared to normal zones. To determine if criteria based on canine myocardial thallium-201 clearance rates could be applied clinically, 40 patients with and 26 patients without coronary artery disease (CAD) had serial thallium-201 images obtained for 2 to 5 hours after dipyridamole. Regions of interest were manually placed over six left ventricular segments in two projections for each of three imaging times. The myocardial thallium-201 clearance rate was calculated for each of the six segments and, using the clearance rate criterion found in canine studies, was considered abnormal if less than 6.5%/hr. Using this criterion alone, 22 of 26 patients (85%) without CAD had normal and 30 of 40 patients (75%) with CAD had abnormal myocardial thallium-201 clearance rates. A quantitative analysis of regional inhomogeneity in tracer distribution (normal was greater than or equal to 25% difference between segments) was negative in 24 of 26 patients (92%) without CAD and positive in 20 of 40 patients (50%) with CAD. When both clearance rate and regional inhomogeneity were considered, 21 of 26 patients (81%) without CAD had negative and 36 of 40 patients (90%) with CAD had positive results. Thus, post-dipyridamole myocardial clearance rate criteria derived from canine studies can be applied to clinical thallium imaging. Quantitative analysis of serial thallium-201 images after dipyridamole is optimized by using myocardial thallium-201 clearance rates. Such an approach is independent of regional inhomogeneities in tracer distribution.

Adult↗

PubMed1984

A new approach to quantitation of exercise thallium-201 scintigraphy before and after an intervention: application to define the impact of coronary angioplasty on regional myocardial perfusion.

We have developed a new computer method designed to quantitate regional myocardial thallium-201 (TI-201) initial distribution, redistribution, and clearance rate. In addition, this computer method permits the generation of functional images to compare two thallium images in the same projection to one another. These functional images can be used to demonstrate the extent of redistribution and the extent of change in regional perfusion before and after an intervention. To validate and apply this new computer technique, exercise TI-201 myocardial images obtained before and 1 week after percutaneous transluminal coronary angioplasty (PTCA) were analyzed in 20 patients with isolated left anterior descending coronary artery disease. Significant improvement in initial TI-201 activity, expressed as a percentage of maximal myocardial activity, was present in the anterior (71.9 +/- 12.0 to 84.1 +/- 11.5%, p less than 0.001) and septal (66.7 +/- 15.4 to 75.2 +/- 11.0%, p less than 0.05) regions of the left ventricle 1 week after PTCA. This increase in relative anterior wall TI-201 uptake was associated with a significant reduction in the amount of TI-201 redistribution between initial and delayed postexercise images (14.7 +/- 14.6 to 3.0 +/- 13.2%, p less than 0.05) as well as an increase in TI-201 clearance rate (t 1/2 from 8.8 +/- 4.4 to 4.3 +/- 2.5 hours, p less than 0.001). Quantitative analysis of TI-201 scans demonstrated improvement in 14 of 20 patients following PTCA. Computer-derived functional difference images depicted diminution in the extent of ischemia as manifested by redistribution of TI-201.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

A comparison of the technetium-labeled myocardial agents DiArs and DMPE to 201Tl in experimental animals.

The biodistribution, kinetics, imaging characteristics and blood flow correlations of 99mTc labeled DiArs and DMPE were studied. The mice biodistribution were compared to 201Tl in mice and dogs, respectively. The myocardial kinetics of these agents were evaluated in normal and ischemic myocardium using miniaturized endocardial detectors. DiArs had a lower myocardial concentration (9.4 +/- 0.8% dose/g at 1 min), than DMPE (11.7 +/- 1.1% dose/g at 1 min) but both were considerably less than 201Tl (23-26% dose/g at 1 min). The kinetic characteristic of both technetium labeled agents suggested that redistribution into ischemic myocardium would not take place, since the clearance rate from normal and ischemic myocardium was similar for both the DiArs and DMPE . The clear visualization of the canine myocardium after i.v. injection demonstrated the superiority of DMPE over DiArs and the potential use of these agents, if proven, to behave the same in human trials.

Animals↗

PubMed1984

Comparison of exercise perfusion and ventricular function imaging: an analysis of factors affecting the diagnostic accuracy of each technique.

Exercise thallium-201 perfusion scans and gated equilibrium blood pool scans were performed in 120 catheterized patients with a chest pain syndrome. Eighty-six patients had coronary artery disease and 34 patients did not. The effects of gender, propranolol, exercise level, exercise ischemia, history of typical angina, history of previous myocardial infarction, electrocardiographic Q waves, number of diseases vessels and extent of coronary artery obstruction on diagnostic accuracy were evaluated. The overall sensitivity and specificity of thallium scans were 76 and 68%, respectively, and those of gated blood pool scans 80 and 62% (p = not significant). Propranolol decreased the specificity of thallium scans (propranolol = 42%; no propranolol = 87%, p less than 0.05). Thallium scans and anginal history were less sensitive for detecting coronary disease in women (men: thallium = 79%; angina = 77%; women: 54 and 46%, respectively; p less than 0.05). Exercise level did not significantly affect the diagnostic accuracy of either scan. Thallium and gated scans were both highly sensitive (95%) in detecting disease in 20 patients with a prior myocardial infarction, angina and a positive electrocardiogram. The sensitivity of the thallium scan significantly decreased as the number of diseased vessels decreased. Both thallium and gated scans were less frequently positive in patients with atypical angina or no Q waves, but were not significantly influenced by electrocardiographic ischemia. The sensitivity and specificity of both scans were low in 57 patients with the combination of atypical angina, no history of infarction and equivocal stress electrocardiogram thallium = 61 and 63%, respectively; gated = 61 and 67%). When stress thallium scan evaluation included the electrocardiogram and thallium scan interpretation, the diagnostic accuracy was 81%. When all the information from gated scans (wall motion, ejection fraction, pulmonary blood volume) was combined for final gated scan evaluation, the diagnostic accuracy was 83%. When electrocardiographic data were added to all three gated scan variables, diagnostic accuracy was 77%. In conclusion, thallium perfusion and gated blood pool scans have reasonable diagnostic accuracy for coronary artery disease in a group of patients with a moderately high prevalence of disease. However, combined variables from each test are needed to provide reliable diagnostic accuracy.

Coronary Circulation↗

PubMed1984

Contrast echocardiography in acute myocardial ischemia: I. In vivo determination of total left ventricular "area at risk".

Myocardial contrast echocardiography has been shown recently to accurately assess the "area at risk" for necrosis after acute coronary occlusion in the experimental model. Risk area quantitation, however, has been studied primarily from single tomographic planes. Because the three-dimensional extent of myocardial necrosis depends on the total volume of myocardium at risk, the total left ventricular "area at risk" was determined in 11 dogs (Group A) with either left anterior descending or left circumflex artery occlusion using contrast echocardiography and compared with risk area determined by technetium autoradiography. An excellent correlation was found between the two methods (r = 0.96%, y = 0.91x + 1.5, p less than 0.001, SEE = 3.17). A comparison of risk area for individual levels of the left ventricle using both methods, however, showed some variation in the degree of correlation, with the poorest fit being apparent at the apex. To identify the source of the variation, errors caused by data registration were minimized in six additional dogs (Group B) by implanting epicardial markers at a single level and measuring "area at risk" at this level using both methods. When no registration error was present, the correlation between the two methods was excellent (r = 0.99, y = 0.92x + 2.6, p less than 0.001, SEE = 0.55). In conclusion, the "area at risk" for infarction after acute coronary occlusion can be determined accurately for the entire left ventricle as well as for a single tomographic slice using myocardial contrast echocardiography. This was validated using technetium autoradiography, which is an established method of determining "area at risk" in the experimental setting.

Animals↗

PubMed1984

Kinetics of thallium-201 in reperfused canine myocardium after coronary artery occlusion.

To study the kinetics of thallium-201 in nonsalvaged acutely infarcted myocardium and salvaged myocardium, the tracer was administered after experimental left anterior descending coronary artery reperfusion 2 hours after occlusion. In 19 dogs, thallium activity was then monitored for 4 hours in the reperfused anterior wall and normal posterior wall using miniature cadmium telluride radiation detectors. After sacrifice, 13 of the dogs were found to have an infarcted anterior wall by triphenyltetrazolium-chloride staining. In these dogs, mean (+/- standard deviation) fractional 4 hour thallium clearance was 0.33 +/- 0.08 for the infarct zone and 0.15 +/- 0.06 for the normal control zone (p less than 0.001). When computer-modeled, the clearance curve from the infarct zone was biexponential. The second exponential clearance curve from the infarct zone began 19.1 +/- 3.2 minutes after tracer administration, and was indistinguishable from the monoexponential clearance curve from the normal control zone. Thallium clearance from the blood pool was triexponential, the final exponential clearance curve being indistinguishable from the normal control zone clearance curve. Six dogs were found to have a salvaged noninfarcted anterior wall by triphenyltetrazolium-chloride staining. In these dogs, mean fractional 4 hour thallium clearance was 0.20 +/- 0.07 for the reperfused zone, and 0.19 +/- 0.08 for the normal control zone (p = NS). When computer-modeled, clearance curves for the reperfused and control zones were monoexponential. The monoexponential clearance curve for the salvaged reperfused zone was indistinguishable from the monoexponential clearance curve for normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Effect of decreased blood flow and ischemia on myocardial thallium clearance.

To determine the effect of reduced coronary blood flow on myocardial thallium-201 clearance over a range of flows, miniature radiation detectors were inserted into the left ventricular apex and positioned against the anterior and posterior endocardial walls in 21 dogs. Thallium was administered intravenously and myocardial tracer activity was monitored continuously for 1 hour in both walls. A balloon occluder was then partially inflated around the left anterior descending coronary artery in 19 dogs, producing a range of anterior wall blood flow reductions as assessed by the microsphere technique. Thallium activity was monitored continuously for 3 hours in both walls. Two dogs served as control animals and had no coronary artery occlusion at 1 hour. At the end of the 4 hour experiment, the dogs were sacrificed and the hearts counted in a well counter. The 19 dogs with coronary artery stenosis were divided into three groups (mild, moderate and severe flow reduction groups) on the basis of their poststenosis anterior/posterior wall regional myocardial blood flow ratios. The two control dogs had similar thallium clearances in the anterior and posterior left ventricular walls during the 3 hour period, as assessed by the radiation detectors, and by a final anterior/posterior wall thallium ratio near unity. All three groups of dogs with coronary stenosis had comparable fractional thallium clearances from the anterior and posterior walls before and after the balloon occluder inflation. The final anterior/posterior left ventricular wall thallium ratios were not significantly different than unity for all three groups of dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Right ventricular ejection fraction response to exercise in patients with coronary artery disease: influence of both right coronary artery disease and exercise-induced changes in right ventricular afterload.

To determine the influence of proximal right coronary artery disease and right ventricular afterload on right ventricular ejection fraction response to exercise, 64 patients were studied at rest and after supine exercise with gated equilibrium radionuclide angiography and coronary angiography. Right ventricular afterload response to exercise was estimated from determinations of exercise-induced changes in pulmonary blood volume, previously shown to correlate with exercise-induced changes in pulmonary capillary wedge pressure. Values for right ventricular ejection fraction decreased from rest to exercise (48 +/- 5% to 42 +/- 9%, p less than 0.001) in patients with an elevated pulmonary blood volume ratio. Values were unchanged in patients with isolated proximal right coronary artery disease (rest 49 +/- 3%, exercise 47 +/- 7%), decreased in patients with combined right and left coronary disease (rest 48 +/- 6%, exercise 39 +/- 10%, p less than 0.001) and increased (rest 47 +/- 5%, exercise 52 +/- 6%, p less than 0.001) in patients with isolated left coronary artery disease. To determine the coinfluence of coronary anatomy and changes in pulmonary blood volume, patients were classified by pulmonary blood volume ratio. Among patients with a normal pulmonary blood volume ratio, right ventricular ejection fraction did not change significantly in those with proximal right coronary artery disease during exercise, but increased significantly in patients with isolated left coronary disease. Among patients with an elevated pulmonary blood volume ratio, right ventricular ejection fraction during exercise increased significantly in those with proximal right coronary artery disease but was unchanged in patients with isolated left coronary disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

Quantitation of myocardial infarct size from thallium-201 images: validation of a new approach in an experimental model.

A new computer-based method has been developed to quantitate myocardial infarct size from the size of the regional thallium-201 deficit. The operator outlines the left ventricular myocardial activity with an ellipse. The program then plots the background-corrected activities of the highest mean value in a 3 pixel myocardial band perpendicular to and within the ellipse. The approach uses a new interpolative background correction. To determine the accuracy of this approach in assessing regional thallium deficit size, acute myocardial infarction was produced in six dogs by 24 hour occlusion of the proximal left anterior descending coronary artery. Infarct size was assessed from planar thallium images of the dog heart in three views, each with the chest opened and closed and with the heart excised and placed in a cradle. Before removal of the heart, triphenyltetrazolium chloride was infused to delineate normal from infarct tissue. Transverse slices of left ventricle were made and thallium images of the slices acquired. Infarct size delineated by triphenyltetrazolium chloride staining was expressed as a percent of the total left ventricular slice surface area (planimetric infarct size). Infarct size from whole heart and left ventricular slice thallium images was expressed as a percent of the total length of the left ventricular perimeter (perimetric infarct size). This was determined from points below a certain percent of normalized peak thallium activity in the computer-generated thallium activity curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

The use of preintervention and postintervention thallium imaging for assessing the early and late effects of experimental coronary arterial reperfusion in dogs.

To determine if thallium-201 imaging of myocardial perfusion can be used as an early predictor of myocardial salvage after reperfusion, 24 adult dogs were subjected to complete occlusion of the left anterior descending coronary artery with release of the snare 2 hr later. Separate doses of thallium (1 mCi) and microspheres were given 15 min before, 5 min after, and 1 hr after release of the snare. Gamma camera images of the heart were obtained after each injection of thallium. Preinjection images were also acquired before the second and third doses and were subtracted from the postinjection images to eliminate the counts due to residual activity from the prior injections. The chest was then closed and the dog allowed to recover. The chest was reopened 48 hr later, final doses of thallium and microspheres were administered, and the heart was imaged. After the dog was killed, the left ventricle was sliced from apex to base, and any infarct was outlined with triphenyltetrazolium (TTC) staining. The slices were then subdivided into pieces of approximately 1 g each and then well counted for microsphere determination of regional myocardial blood flows. Thallium images were interpreted qualitatively and quantitatively. Fifteen dogs with myocardial infarctions, as assessed by TTC staining, all had thallium image defects during coronary arterial occlusion. Thallium scans obtained immediately after reperfusion demonstrated increased anterior wall thallium activity in nine dogs, normal activity in four dogs, and decreased activity in two dogs. In 14 of the 15 dogs, relative thallium activity correlated with the occlusion/normal zone flow ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗