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Biomedical subjects

J L Weiss

Publications and source records attributed to J L Weiss.

At least 19 recordsLinked to original sources
PubMed1992

Dissociation between left ventricular untwisting and filling. Accentuation by catecholamines.

BACKGROUND: Efficient early diastolic filling is essential for normal cardiac function. Diastolic suction, as evidenced by a decreasing left ventricular pressure during early filling, could result from restoring forces (the release of potential energy stored during systolic deformation) dependent on myofilament relaxation. Although these restoring forces have been envisioned within individual myofibers, recent studies suggest that gross fiber rearrangement involving the connective tissue network occurs easy in diastole. This may lead to the release of potential energy stored during systole and suction-aided filling. METHODS AND RESULTS: To establish precisely the timing and extent of restoration of the systolic torsional deformation of the left ventricle with respect to early filling at baseline and with enhanced relaxation, we studied untwisting during control conditions and with catecholamine stimulation. Using noninvasive and nondestructive magnetic resonance tagging, torsional deformation of the left ventricle was measured at 20-msec intervals in 10 open-chest, atrially paced dogs, starting at aortic valve closure. Eight equiangular tags intersected the epicardium and endocardium in three short-axis imaging planes (base, mid, and apex). From the intersection points, epicardial and endocardial circumferential chord and arc lengths were measured and angular twist of mid and apical levels with respect to the base (maximal torsion and its reversal, untwisting) was calculated. Echo-Doppler provided timing of aortic valve closure and of mitral valve opening. Zero torsion was defined at end diastole. Torsion at the apical level reversed rapidly between its maximum and the time immediately after mitral valve opening: from 7.0 +/- 5.8 degrees to 3.2 +/- 5.4 degrees and 12.0 +/- 8.5 degrees to 6.9 +/- 7.8 degrees (mean +/- SD, both p less than 0.01) at the epicardium and endocardium, respectively. During the same period, no significant circumferential segment length changes occurred. As expected, after mitral valve opening, filling resulted in significant circumferential segment lengthening, whereas further reversal of torsion was small and nonsignificant. During dobutamine infusion, torsion at end systole was greater and reversal during isovolumic relaxation was much more rapid and greater in extent (p less than 0.01). Torsion reversed from 11.5 +/- 4.3 degrees to 5.7 +/- 4.8 degrees and 17.4 +/- 6.4 degrees to 6.9 +/- 7.7 degrees at epicardium and endocardium. CONCLUSIONS: Untwisting occurs principally during isovolumic relaxation before filling and is markedly enhanced in speed and magnitude by catecholamines. This partial return of the left ventricle to its preejection configuration before mitral valve opening could represent an important mechanism for the release of potential energy stored in elastic elements during the systolic deformation. These myocardial restoring forces would be markedly enhanced by physiological changes consequent to catecholamines such as during exercise, offsetting the concomitant shortening of the filling period.

Animals↗
PubMed1991

Myocardial infarct expansion: recognition, significance and pathology.

Infarct expansion can be defined pathologically as a distortion of ventricular topography produced by thinning and disproportionate dilation of the infarct segment. Large transmural infarcts tend to be associated with greater propensity for infarct expansion. Two-dimensional echocardiography has made it feasible to detect these acute alterations in cardiac topography by serial examination of patients with acute myocardial infarction. A practical approach to the echocardiographic quantification of expansion involves analysis of end-diastolic cross-sectional echo views at the papillary muscle level, which can be used as fixed internal landmarks to divide the left ventricle into 2 segments, anterior and posterior. An off-line computer system can be used to track relative lengths of these segments as well as their thicknesses over time. In the initial clinical study, one third of patients with acute anterior transmural infarcts showed an average 50% increase in the infarct segment length beginning within the first 3 days of infarction, characterized by disproportionate progressive dilation and transmural thinning of this zone. These patients demonstrated a significantly higher mortality than those without expansion. Later studies demonstrated not only continuing dilation of the infarcted anterior wall, but also progressive dilation of the noninfarcted posterior wall, underscoring the importance of continuing long-term noninvasive follow-up. Not only is expansion associated with a poor clinical outcome; it has also been shown experimentally and clinically to be modifiable or even preventable by various therapeutic maneuvers, which may well improve survival. Because of the limitations of the echocardiographic window, it is often possible to obtain only a single cross-sectional view of high quality, and even then technical quality may not be sufficiently high to enable detailed quantitative analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Reduced left ventricular cavitary activity ("black hole sign") in thallium-201 SPECT perfusion images of anteroapical transmural myocardial infarction.

Apparently reduced left ventricular (LV) cavitary thallium activity in both planar and tomographic perfusion images has been previously observed by these and other investigators. With single-photon emission computerized tomography, we have clinically noted that this "black hole sign" was associated with an aneurysm in the setting of a transmural anterior or anteroapical perfusion defect. We have now prospectively studied the etiology and predictive value of this sign in 84 consecutive patients with an anterior, anteroapical transmural perfusion defect. Of the 84 patients, 49 had both LV aneurysm (confirmed by contrast ventriculography, echocardiography or gated blood pool studies) and a black hole sign. Only 1 patient with an aneurysm did not have the black hole sign, and 2 without aneurysm did. Thus, it is concluded that this sign is highly accurate in diagnosing LV aneurysm. Because thallium-201 single-photon emission computerized tomography imaging is often performed as one of the first diagnostic tests soon after myocardial infarction, this has important clinical management implications.

Adult↗
PubMed1991

Usefulness of OPC-8212, a quinolinone derivative, for chronic congestive heart failure in patients with ischemic heart disease or idiopathic dilated cardiomyopathy.

To evaluate the safety and efficacy of the inotropic agent OPC-8212 in patients with chronic congestive heart failure, 76 patients with impaired cardiac function and diminished exercise tolerance were studied. They were randomized to 12 weeks of double-blind therapy with either 60 mg/day of OPC-8212 or placebo. The study drug was added to their baseline medical regimen. The primary study outcome was the combined outcome of the time to either mortality (of all cause) or substantial worsening of heart failure (major morbidity), whichever occurred first. Treatment with OPC-8212 significantly (p less than 0.01) decreased the combination of major morbidity/mortality over 12 weeks of therapy. Quality of life, assessed by the Sickness Impact Profile questionnaire, was significantly improved in patients receiving OPC-8212 (p less than 0.01). Furthermore, ventricular premature contractions as assessed by 24-hour Holter monitoring were not increased with OPC-8212 treatment. Although patients treated with OPC-8212 were able to reach a significantly higher peak oxygen uptake and exercise longer during symptom-limited exercise, when data were analyzed as percent change from baseline, the absolute increases were small. These results suggest that OPC-8212 is beneficial in treating patients with congestive heart failure and that further evaluation of this new inotropic agent is warranted.

Adolescent↗
PubMed1991

Estimating WAIS-R IQ from the Shipley Institute of Living Scale: a replication.

Zachary, Crumpton, and Spiegel (1985) introduced a linear regression and continuous norming procedure for estimating Full Scale WAIS-R IQ from the Shipley Institute of Living Scale. The present study replicated their method with 55 adult psychiatric inpatients and day hospital patients. A high correlation (r = .85), an extremely small mean difference in IQ (.8 points), and an acceptable average absolute difference (7.6 points) were found between estimated and obtained WAIS-R. Sines and Simmons tables (1959) for Shipley estimates of WAIS IQ produced a high correlation (r = .86), but large mean and average absolute differences (13.1 and 13.6 points, respectively). The study supports use of the Zachary et al. procedure for estimating WAIS-R IQ from Shipley scores in a psychiatric population.

Adolescent↗
PubMed1991

Circumferential anterior- and posterior-based wedge keratectomies: novel refractive procedures.

Wedge resections have been demonstrated to have significant effects on the curvature of the cornea in the meridian of the resection. This paper describes two complimentary, noninvasive, circumferential wedge keratectomy techniques for the correction of spherical ametropia. Eleven eye bank eyes were studied. Four eyes underwent the circumferential anterior-based wedge (ABW) keratectomy technique in an attempt to induce steepening of the cornea. Seven eyes underwent the circumferential posterior-based wedge (PBW) keratectomy in an attempt to flatten the cornea. The mean steepening of 4.86 +/- 1.79 diopters in the ABW group was statistically significant (p less than 0.01). The mean flattening of 7.47 +/- 4.46 diopters in the PBW group was also found to be significant (p less than 0.01). These techniques are presented as viable alternatives to relaxing incision techniques such as radial keratotomy. Further refinement of the technique and improved technology will make these techniques more predictable and reliable.

Cornea↗
PubMed1991

Quantification of and correction for left ventricular systolic long-axis shortening by magnetic resonance tissue tagging and slice isolation.

BACKGROUND: Measurement of regional left ventricular (LV) function is predicted on the ability to compare equivalent LV segments at different time points during the cardiac cycle. Standard techniques of short-axis acquisition in two-dimensional echocardiography, cine computed tomography, and standard magnetic resonance imaging (MRI) acquire images from a fixed plane and fail to compensate for through-plane motion. The shortening of the left ventricle along its long axis during systole results in planar images of two different levels of the ventricle, leading to error in any derived functional measurements. LV systolic long-axis motion was measured in 19 normal volunteers using MRI. METHODS AND RESULTS: With a selective radio frequency (RF) tissue-tagging technique, three short-axis planes were labeled at end diastole and standard spin-echo images were acquired at end systole in the two- and four-chamber orientations. Persistence of the tags through systole allowed visualization of the intersecting short-axis tags in the long-axis images and allowed precise quantification of long-axis motion of the septum, lateral, anterior, and inferior walls at the base, mid, and apical LV levels. The total change in position along the long axis between end diastole and end systole was greatest at the base, which moved toward the apex 12.8 +/- 3.8 mm. The mid left ventricle moved 6.9 +/- 2.6 mm, and the apex was nearly stationary, moving only 1.6 +/- 2.2 mm (p less than 0.001). Having quantified the normal range of long-axis shortening, we developed a technique that isolates a slice of tissue between selective RF saturation planes at end diastole. Combining this with a wide end-systolic image slice, end-systolic images were acquired without contamination of signal from adjacent tissue moving into the imaging plane. This technique was validated in a moving phantom and in normal volunteers. CONCLUSIONS: Significant LV systolic long-axis shortening exists, and this effect is seen the most at the base and the least at the apex. At a given ventricular level, shortening varied significantly according to location. A method using selective saturation pulses and gated spin-echo MRI automatically corrects for this motion and thus eliminates misregistration artifact from regional function analysis.

Evaluation Studies as Topic↗
PubMed1991

Air/liquid corneal organ culture: a light microscopic study.

Air/liquid organ culture of tissues with stratified epithelial layers has been shown to encourage tight packing of cells and promote cellular differentiation. In this study human corneas cultured in a air/liquid environment were compared to paired, conventionally-cultured corneas to determine if the long-term morphology could be improved. Fourteen paired human corneas were cultured at 37 degrees C in covered culture dishes for 1 to 3 weeks. Air/liquid cultured corneas were placed epithelial-side up in a fixed position and culture medium was added to a level so that during rocking the corneal epithelia were intermittently exposed to air/liquid environments. Mate corneas were cultured using the conventional method. In this method corneas are fully submerged, epithelial-side down, in culture medium. After 3 weeks of culture significantly less epithelial intercellular edema was noted for the air/liquid cultures (p = 0.033), compared to conventional cultures. Significant improvements in cellular structure of the endothelial layers, after 1 and 3 weeks incubation (p = 0.029 and 0.000) and stromal layers, after 3 weeks in culture (p = 0.024), were also noted. We have shown that slight modifications of the organ culture environment lead to improvements in corneal morphology. Air/liquid corneal organ culture has promise for use in corneal wound healing studies and long-term culture.

Aged↗
PubMed1990

The effects of antihypertensive therapy on left ventricular mass in elderly patients.

Left ventricular mass sometimes decreases during treatment of hypertension, but this response is inconsistent and its effects on left ventricular function are unknown. In a six-month randomized trial, we studied the ability of verapamil and atenolol to reduce left ventricular mass in 42 elderly patients with hypertension and the effects of this reduction in mass on cardiac function. The mean blood pressure (+/- SE) decreased in both the group that received verapamil (from 171.4 +/- 3.2/93.0 +/- 2.5 mm Hg to 142.9 +/- 2.8/79.0 +/- 2.0 mm Hg) and the group that received atenolol (from 179.6 +/- 4.6/98.5 +/- 2.4 mm Hg to 148.1 +/- 3.3/83.4 +/- 1.2 mm Hg), but the atenolol-treated patients more frequently required the addition of chlorthalidone to achieve blood-pressure reduction (P less than 0.01). Verapamil resulted in a reduction in the left-ventricular-mass index from 104 +/- 5 g per square meter of body-surface area to 85 +/- 5 g per square meter (P less than 0.01). Atenolol did not produce a reduction in the left-ventricular-mass index (109 +/- 9 g per square meter before treatment vs. 112 +/- 10 g per square meter after treatment). Two weeks after the withdrawal of antihypertensive therapy, blood pressure returned to pretreatment values. Nevertheless, in patients whose left ventricular mass had decreased, two measures of diastolic filling, the peak diastolic filling rate to the peak ejection rate, were significantly higher than before treatment (2.42 +/- 0.2 vs. 3.31 +/- 0.4 [P less than 0.05] and 0.61 +/- 0.03 to 0.85 +/- 0.05 [P less than 0.05], respectively). Diastolic filling was unchanged in the group that had no reduction in left ventricular mass. Cardiac output and the ejection fraction at rest and during mild exercise were unchanged in both groups as compared with baseline values. We conclude that left ventricular mass can be reduced in elderly patients with hypertension and mild ventricular hypertrophy who receive antihypertensive therapy. Reduction occurs more frequently with verapamil than with atenolol therapy, increases diastolic filling, and does not impair systolic function.

Atenolol↗
PubMed1990

Contrast echocardiographic mapping of collateralized myocardium in humans before and after coronary angioplasty.

Conventional coronary arteriography is able to demonstrate the presence of coronary collateral vessels but cannot delineate the specific region of myocardium to which they supply blood. To test the hypothesis that contrast echocardiography can specifically identify collateralized myocardium, contrast echocardiographic perfusion "maps" were compared in patients with (n = 12) and without (n = 12) angiographic evidence of coronary collateral flow, both before and after coronary angioplasty. Contrast echocardiographic images of the mid-left ventricle in the short-axis view at end-diastole were obtained after separate injections of a sonicated contrast agent into both the right and the left coronary arteries. A computer-based contouring system was used to determine the individual areas of myocardium perfused by each of the two coronary arteries and then to superimpose the images of the two perfusion beds. The resulting area of overlapping perfusion represented myocardium receiving blood flow from both coronary systems and was defined as collateralized myocardium. To normalize for heart size, overlap area was expressed as a percent of total myocardial area, which was the area between endocardium and epicardium in the short-axis view. To adjust for differences in vascular distribution, overlap area was expressed as a percent of the perfusion area of the recipient vessel. In patients with angiographic collateral flow, the recipient vessel was that vessel receiving the collateral flow. In patients without angiographic collateral flow, the right coronary artery was considered the recipient vessel. Overlap area was 1.3 +/- 0.4% of total myocardial area and 6.6 +/- 1.7% of recipient vessel area in patients without angiographic evidence of collateral flow compared with 30.6 +/- 2.5% and 89.2 +/- 6.4%, respectively, in patients with angiographic collateral flow (p less than 0.001 for both). In four patients in whom angiographic collateral flow was abolished by angioplasty, overlap area decreased from 30.3 +/- 5.3% to 6.8 +/- 2.7% of total myocardial area and from 100% to 18.5 +/- 5.4% of recipient vessel area (p less than 0.05 for both). Thus, contrast echocardiography is able to map the specific myocardial territory perfused by coronary collateral flow and document an immediate reduction in perfusion in this territory when collateral flow is abolished by angioplasty.

Angioplasty, Balloon, Coronary↗
PubMed1990

Magnetic resonance imaging as a noninvasive standard for the quantitative evaluation of left ventricular mass, ischemia, and infarction.

Because magnetic resonance imaging (MRI) acquires data in a spatially unambiguous fashion and the three-dimensional interrelationships of one image plane to another are easily ascertained, there are far fewer technical restrictions imposed on this method than on other imaging techniques. Furthermore, the multiplanar nature of MRI image acquisition, in any plane desired, is a feature unique to this imaging technology. MRI is thus well suited to the highly accurate quantification of global and regional left ventricular (LV) size and function, and can be used as a standard for comparison to other techniques, once validated. Because the determination of LV mass by MRI requires no assumptions about ventricular shape, it should be well suited to the evaluation of both normal hearts and those distorted by infarction. We performed gated MRI on 15 dogs before and after myocardial infarction. LV mass was calculated with 5 short axis planes. The correlation was excellent between actual mass before infarction and after MI. Accuracy was similar for both end-diastole and end-systole. Thus, MRI accurately determines LV mass in both distorted and normal hearts. We have also developed a method for quantification and mapping of regional wall thickening throughout the LV as an index of regional ischemia by utilizing the 3D geometry to calculate the perpendicular wall thickness of a 3D volume element of tissue. This 3D volume element results in less variability of normal wall thickening and provides a better discriminator of ischemic from nonischemic zones in a canine model of acute ischemia, whereas there is considerably greater overlap between ischemic and normal zones with standard planar MRI techniques. The 3D method is more accurate than planar methods in avoiding biases resulting from the oblique course of an image plane through the LV wall, resulting in better distinction of ischemic from nonischemic tissue. Finally, the accurate assessment of regional LV function for the identification of ischemic or infarcted myocardium has been enhanced greatly by a new technique, myocardial tissue tagging, in which an electronic marker is applied to the myocardium which persists through ejection, enabling the accurate tracking of specific areas of the heart as they move and rotate through the cardiac cycle.

Cardiomegaly↗
PubMed1990

Three-dimensional mapping of acute ischemic regions using MRI: wall thickening versus motion analysis.

Three-dimensional (3D) endocardial wall motion and thickening were compared as quantitative methods for distinguishing ischemic from non-ischemic myocardium and for their potential to map regional left ventricular (LV) function. Data were obtained by gated magnetic resonance (MR) images in seven open-chest dogs with acute ischemia. The LVs were reconstructed in 3D at end diastole (ED) and end systole (ES) with a helical coordinate system that wraps the endocardium and epicardium. Thickness and percent wall thickening were calculated by a 3D volume element method. Wall motion was calculated by the 3D displacement of the endocardium perpendicular to the wall using both fixed and floating centroids. Monastral blue nonstaining identified the ischemic regions from five anatomical slices of the LV, which corresponded to the in vivo image planes. Thickening and motion were compared at the centers of the ischemic and the remote normal zones, in addition to comparing the functional maps of the entire LV to the postmortem anatomical maps. All methods distinguished between the center of the ischemic zone and the remote normal zone; however, thickening discriminated most strongly between zones. Comparison of the 3D in vivo maps with the 3D postmortem maps showed that the sensitivity, specificity, and overall accuracy of the thickening algorithm exceeded those obtained by the wall motion algorithms with fixed or floating centroids. Thus wall thickening utilizing the 3D volume element approach is superior to 3D wall motion algorithms in distinguishing ischemic from nonischemic zones and in mapping regional function in the entire LV.

Acute Disease↗
PubMed1990

Quantification and validation of left ventricular wall thickening by a three-dimensional volume element magnetic resonance imaging approach.

We have developed a method to quantify and map regional wall thickening throughout the left ventricle (LV) with magnetic resonance imaging. In contrast to methods that measure planar wall thickness and thickening, this method uses the three-dimensional (3D) geometry of the left ventricle to calculate the perpendicular thickness of the wall. We tested this method at three levels of increasing complexity using 1) phantom studies, 2) in vivo experiments in dogs with normal cardiac function, and 3) in vivo studies in dogs during acute ischemia. Experiments were conducted in 15 open-chest dogs imaged by a 0.38 T iron core magnet. Five short-axis images at end diastole and end systole were obtained with the spin echo technique by use of the QRS as a trigger for end diastole and the second heart sound, S2, to time end systole. After acquisition of preischemic images, acute ischemia was induced by either coronary artery ligation (n = 5) or intracoronary dental rubber injection (n = 5), which produced severe transmural ischemia. By use of computer-aided contouring of the endocardial and epicardial borders, each image was divided into 16 segments with radial lines originating from the midwall centroid. A 3D volume element was defined as that generated by connecting two matched planar segments in two adjacent image planes. This defined 64 volume elements comprising the entire left ventricle. Thickness and thickening before and during ischemia were then calculated by using the planar segments and the 3D volume elements. In phantom studies, the 3D method was accurate, independent of the angle of inclination of the image plane to the phantom wall, whereas the planar method showed considerable overestimation of thickness when the image plane was oblique to the phantom wall. In the dogs before induction of ischemia, the 3D method demonstrated the well-established normal taper in end-diastolic wall thickness from 1.10 +/- 0.02 cm at the base to 1.05 +/- 0.11 cm at the apex (p less than 0.01). By contrast, the planar method did not detect the decrease in thickness toward the apex (1.13 +/- 0.07 cm at the base vs. 1.16 +/- 0.14 cm at the apex, p = NS). During acute ischemia, thickening was calculated by both methods at the center of the ischemic zone defined by Monastral blue nonstaining and compared with the preischemic values.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗
PubMed1990

Noninvasive quantification of left ventricular rotational deformation in normal humans using magnetic resonance imaging myocardial tagging.

It has been postulated that rotation of the left ventricular apex with respect to the base is a component of normal systolic function in humans, but it has been difficult to measure it noninvasively. Tagging is a new magnetic resonance imaging technique that labels specific areas of myocardium by selective radio-frequency excitation of narrow planes orthogonal to the imaging plane before acquiring an image. Tags appear as black lines and persist in myocardium for 400-500 msec and, if applied at end diastole, will move with the myocardium through systole. Tagging was used to noninvasively quantify left ventricular torsion and circumferential-longitudinal shear (shearCL) in humans. Eight normal volunteers, aged 24-38 years, were imaged in a 0.38-T iron-core resistive magnet. Five short-axis left ventricular images, positioned to encompass the entire left ventricle (LV), were obtained separately at end systole. Four equiangular radial tags had been applied at end diastole, intersecting the myocardium at eight locations. We calculated the difference in angular displacement of each epicardial and endocardial tag point (a tag point being where the tag crossed the epicardium or endocardium) at end systole from the systolic position of the corresponding tag point on the basal plane. This value was called the torsion angle. From this, shearCL, the angle inscribed on the epicardial or endocardial surface between the systolic tag position, the corresponding basal tag position, and its projection onto the slice of interest could be calculated at 32 points in the left ventricular wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

A comparison of retrobulbar and periocular anesthesia for cataract surgery.

Complications of retrobulbar anesthesia are rare but significant. Periocular anesthesia has been advocated as an alternative to retrobulbar injections. In a prospective, randomized, masked study of 79 consecutive cataract extractions with intraocular lens implantations, 40 patients received retrobulbar injections and 39 patients received periocular injections. In every instance, the volume of the injection was 5 mL. No significant difference in surgeon's assessment of akinesia and anesthesia was found. Supplemental anesthesia was required in eight (21%) of the patients who received retrobulbar injections and in 11 (28%) of the patients who received periocular injections. A significant increase in chemosis was found with periocular injections. There was one complication with retrobulbar anesthesia and none with periocular anesthesia. No significant difference in patient assessment of comfort was found. The efficacy of periocular anesthesia appears to be comparable to that of retrobulbar anesthesia.

Anesthesia↗
PubMed1989

Influence of site of regional ischemia on nonischemic thickening in anesthetized dogs.

The effect of varying the site of acute regional ischemia on nonischemic myocardial function was examined by comparing regional thickening during 2-3 min circumflex (Circ) vs. left anterior descending (LAD) coronary artery occlusions in eight open-chest dogs. Cross-sectional midwall two-dimensional echocardiograms were obtained, and systolic thickening was measured at 16 equal-spaced points around the circumference. The distribution and extent of hypoperfusion was assessed by radiolabeled microspheres. The echo slice was subdivided into a hypoperfused region (Hypo), four adjacent nonischemic regions (ADJ1-4), and the remaining remote segments (Remote). The extent of hypoperfusion (%LV mass) was similar with both sets of occlusions (LAD, 29.4 +/- 2.8%; Circ, 26.0 +/- 4.4%; P = NS), as was endo- and epicardial flow in the nonischemic regions. Yet, even with like-sized Hypo regions, thickening of nonischemic myocardium was significantly greater during Circ than during LAD occlusions (P less than 0.001). These results are consistent with recently reported disparities of global functional impairment during LAD vs. Circ ischemia. The responses likely reflect differences in regional wall geometry, loading, and the three-dimensional distribution of coronary hypoperfusion between the two vascular territories.

Anesthesia↗