In vivo targeting of acoustically reflective liposomes for intravascular and transvascular ultrasonic enhancement.

OBJECTIVES: The purpose of this study was to target acoustically reflective liposomes to atherosclerotic plaques in vivo for ultrasound image enhancement. BACKGROUND: We have previously demonstrated the development of acoustically reflective liposomes that can be conjugated for site-specific acoustic enhancement. This study evaluates the ability of liposomes coupled to antibodies specific for different components of atherosclerotic plaques and thrombi to target and enhance ultrasonic images in vivo. METHODS: Liposomes were prepared with phospholipids and cholesterol using a dehydration/ rehydration method. Antibodies were thiolated for liposome conjugation with N-succinimidyl 3-(2-pyridyldithio) propionate resulting in a thioether linkage between the protein and the phospholipid. Liposomes were conjugated to antifibrinogen or anti-intercellular adhesion molecule-1 (anti-ICAM-1). In a Yucatan miniswine model, atherosclerosis was developed by crush injury of one carotid and one femoral artery and ingestion of a hypercholesterolemic diet. After full plaque development the arteries were imaged (20-MHz intravascular ultrasound catheter and 7.5-MHz transvascular linear probe) after injection of saline, unconjugated liposomes and antibody conjugated liposomes. RESULTS: Conjugated liposomes retained their acoustically reflective properties and provided ultrasonic image enhancement of their targeted structures. Liposomes conjugated to antifibrinogen attached to thrombi and fibrous portions of the atheroma, whereas liposomes conjugated to anti-ICAM-1 attached to early atheroma. CONCLUSIONS: Our data demonstrate that this novel acoustic agent can provide varying targeting with different antibodies with retention of intravascular and transvascular acoustic properties.

Can atherosclerotic coronary arteries vasodilate? An intraoperative high-frequency epicardial echocardiographic study.

Our purpose was to evaluate the vasodilating responses of atherosclerotic coronary arteries using intraoperative high-frequency (12 MHz) epicardial echocardiography. We obtained continuous high-frequency epicardial echocardiographic recordings during surgery, and determined cross-sectional lumen area from 17 coronary arterial segments (12 patients). Nitroglycerin (100 to 400 micrograms/min) was administered intravenously to reduce mean (+/- SEM) arterial pressure 14 +/- 1.8 mm Hg. The cross-sectional arterial images were classified using 3 different parameters: arterial lumen area, percentage of the arterial wall circumference that was atherosclerotic (wall thickness > 0.7 mm), and presence of an eccentrically shaped arterial lumen (maximal/minimal luminal diameter > 1.5). Nine arterial segments had small (< 5.0 mm2) arterial lumens (1.7 +/- 0.40 mm2 [+/- SEM; range 0.6 to 3.9]). With nitroglycerin, the luminal area increased 0.8 +/- 0.28 mm2 (range 0 to 2.5), and 39 +/- 12.1% (range 0 to 117). The remaining 8 segments had larger (> 5.0 mm2) lumens (8.7 +/- 0.91 mm2 [range 5.0 to 11.9]). With nitroglycerin the luminal area increased 4.3 +/- 1.11 mm2 (range 1.4 to 11.4), and 51 +/- 10.2% (range 16 to 96). Seven arterial segments had eccentric lumens; mean maximal/minimal ratio was 1.8 +/- 0.08 (range 1.6 to 2.0). The area increased 39 +/- 7.3% (range 16 to 71) with nitroglycerin. In the 10 concentrically shaped lumens (maximal/minimal lumen diameters 1.3 +/- 0.04 [range 1.1 to 1.5]), nitroglycerin increased luminal area by 48 +/- 12.6% (range 0 to 117) (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of echogenic, plasmid-incorporated, tissue-targeted cationic liposomes that can be used for directed gene delivery.

RATIONALE AND OBJECTIVES: Echogenic antibody-conjugated anionic liposomes have been developed that allow directed tissue targeting and acoustic enhancement. These are not efficient for gene delivery. A cationic formulation that allows directed gene delivery while retaining acoustic properties may provide more efficient transfection. METHODS: Cationic liposomes were prepared and acoustic reflectivity was determined. Anti-fibrinogen-conjugated liposomes were laid on fibrin-coated slides and adherence was quantified using fluorescence techniques. Liposomes were combined with a reporter gene and plated on cell cultures. Human umbilical vein endothelial cells were stimulated to upregulate intercellular adhesion molecule-1 (ICAM-1) and were treated with anti-ICAM-1-conjugated liposomes, and gene expression was quantified. RESULTS: Cationic liposomes retained their acoustic reflectivity and demonstrated specific adherence to fibrin under flow conditions. Significant transfection of human umbilical vein endothelial cells was demonstrated, with higher gene expression seen with specific antibody-conjugated liposomes. CONCLUSIONS: Novel acoustic cationic liposomes have been developed that can be antibody conjugated for site-specific adherence and directed cell modification. This presents exciting potential for a vector that allows tissue enhancement and targeted gene delivery.

A feedback controlled silicon microprobe for quantitative mechanical stimulation of nerve and tissue.

The ability to apply and control the force and force velocity of mechanical stimulation is essential for the study of mechanoelectric transduction and adaptation processes. Silicon micromachining technology was used to produce miniature (20-70 microns wide) mechanical microprobes. Passive polysilicon, piezoresistive, force sensing elements were deposited onto the boron-doped epitaxial silicon and the individual devices were chemically etched from the bulk wafer. These microprobes display a linear force versus output voltage relationship. Stimulation forces up to 2 mN can be generated with a measurement resolution of 1.5 microN. The probes were mounted onto circuit board holders and their output sent to a proportional-integral controller which drives an electromagnetic actuator. By using this force-feedback control circuit coupled to a PC it is possible to define any stimulus wave form pattern and independently control and measure the actual stimulus force and velocity. A computer controlled 3-axis stepper motor (0.025 micron step capability) manipulator is used to position the silicon microprobe-actuator assembly relative to the mechanoreceptive field. Sensor feedback control coupled to the 3-axis stepper motor manipulator allows automatic touchdown control and/or preloading of the probe prior to stimulation. Three-dimensional topographic manipulator feedback position control allows automated receptive field mapping.

The validation of volumetric real-time 3-dimensional echocardiography for the determination of left ventricular function.

The objective of this study was to validate a real-time 3-dimensional echocardiography (3DE) technique for the determination of left ventricular (LV) volume and ejection fraction (EF). In 10 mongrel dogs, an electromagnetic flow (EMF) probe was placed on the aorta, and the thorax was closed. Transthoracic imaging was performed during multiple hemodynamic conditions (n = 58) with simultaneous measurement of stroke volume (SV) with the use of EMF. From the volumetric data set, LV volumes were manually traced off-line by 2 independent observers with an apical rotation method (6 planes) and a conventional method (biplane) in a subset of conditions. This tracing technique was also evaluated in 18 human subjects in whom the calculated EF values were compared with values derived by multigated radionuclide angiography (MUGA). Excellent correlation and close limits of agreement were noted between SV measured by 3DE and EMF (r = 0.93) in dogs. In comparison with EMF-derived SV, 3DE provided better correlation than the biplane method (r = 0.93 versus r = 0.61). Interobserver and intraobserver variabilities were comparable (r = 0.94 and r = 0.94, respectively). In a comparison of MUGA-derived EF values and those obtained by 3DE in human subjects, 3DE provided better correlation than the biplane method (r = 0.94 versus r = 0.85). Real-time 3DE accurately measures left ventricular volumes transthoracically over a wide range of hemodynamic conditions in dogs and accurately determines EF in humans.

Intravascular ultrasound. Three-dimensional applications and forward viewing.

This article provides the reader with some idea of the principles and techniques of three-dimensional reconstruction using intravascular imaging data. The article also describes new intravascular ultrasound imaging devices that have the ability to interrogate the arterial wall ahead of the imaging catheter.

Development of inherently echogenic liposomes as an ultrasonic contrast agent.

Ultrasonic contrast agents have been developed for improved assessment of blood flow and tissue perfusion. Many of these agents are not inherently acoustically reflective (echogenic), and nearly all are not suitable for tissue specific targeting. The purpose of this study was to develop acoustically reflective liposomes, which are suitable for antibody conjugation, without using gas or any other agent entrapment. Echogenic liposomes were prepared from phosphatidylcholine (PC), phophatidylethanolamine (PE), phosphatidylglycerol (PG), and cholesterol (CH), using a dehydration/rehydration method. The formulation was optimized for higher acoustic reflectivity by varying the lipid composition. Liposomes were imaged with a 20 MHz intravascular ultrasonic imaging catheter. Echogenicity levels were expressed using pixel gray scale. The presence of PE and PG at specific concentrations improved echogenicity due to their effects on liposomal morphology as confirmed by freeze-etch electron microscopy. The acoustic reflectivity of liposomes was retained when liposomes were treated with blood at room temperature and 37 degrees C under in vitro conditions. It was demonstrated that the liposomes were also acoustically reflective in vivo after they were injected into a miniswine model. We have developed echogenic liposomes that are stable and suitable for tissue specific targeting as a novel contrast agent. This new contrast agent can be used for ultrasonic image enhancement and/or treatment of targeted pathologic sites.

Force-sensing microprobe for precise stimulation of mechanosensitive tissues.

Quantitative study of the transduction mechanisms in mechanically sensitive nerve terminals has been impeded by the lack of instrumentation with which to generate precisely controlled, physically localized mechanical stimuli. We have developed high-resolution force sensing mechanical microprobes for use in the characterization of such nerve terminals. This paper describes their design, fabrication, and testing. A microprobe is comprised of a 0.5- to 2-mm long silicon cantilever beam projecting from a larger supporting silicon substrate. Acting as the variable leg of a Wheatstone bridge circuit, a piezoresistive polysilicon element located at the base of the beam is used to measure the stimulation force applied at the tip. The microprobes exhibit a stable, linear relationship between the stimulation force and the resulting output voltage signal. Stimulation forces up to 3 mN have been generated with a measurement resolution of 10 microN. These microprobes have been used as the force sensing element of a closed loop feedback-controlled stimulation system capable of stimulating the mechanoreceptive nerve terminals of the rabbit corneal epithelium.

Cannulation of the aortic branches using ultrasound guidance. An animal study.

Catheter placement by ultrasound may reduce radiation, improve positioning, and allow the use of echo contrast agents for diagnostic and therapeutic procedures. To evaluate its utility in the peripheral and coronary vascular beds, a preshaped 20 MHz Doppler catheter was inserted into the femoral artery for renal artery, or into the right carotid artery for left coronary artery cannulation in five dogs. Ultrasonic imaging of the vascular structure and catheter was provided by either transabdominal or transesophageal ultrasound. Using Doppler waveform polarity for retrograde guidance, the catheter was advanced to the region of the left renal or left coronary ostia. Ultrasonic emissions from the Doppler catheter were identified by color Doppler mode of the ultrasound machine and allowed the catheter tip to be identified within the beam width of the scanning transducer, providing the depth dimension. In the two animals in which left renal artery cannulation was attempted, the catheter was successfully manipulated into the ostium. In two of the three animals in which left coronary artery cannulation was attempted, the catheter was successfully manipulated into the ostium, followed by saline contrast injections revealing myocardial perfusion. In addition, in one animal, a Doppler flow wire was identified as it was advanced into the mid circumflex coronary. In conclusion, ultrasonically guided cannulation of aortic branches may be possible without x-ray, and this technique may lead to further use of ultrasound in diagnostic and therapeutic procedures.

Management of asthma.

This paper presents a personal approach to the diagnosis and management of asthma, which is in the author's opinion the most underdiagnosed, underestimated and undertreated condition in medicine.

Human blood and marrow side population stem cell and Stro-1 positive bone marrow stromal cell numbers decline with age, with an increase in quality of surviving stem cells: correlation with cytokines.

Hematological deficiencies increase with aging leading to anemias, reduced hematopoietic stress responses and myelodysplasias. This study tested the hypothesis that side population hematopoietic stem cells (SP-HSC) would decrease with aging, correlating with IGF-1 and IL-6 levels and increases in bone marrow fat. Marrow was obtained from the femoral head and trochanteric region of the femur at surgery for total hip replacement (N=100). Whole trabecular marrow samples were ground in a sterile mortar and pestle and cellularity and fat content determined. Marrow and blood mononuclear cells were stained with Hoechst dye and the SP-HSC profiles acquired. Marrow stromal cells (MSC) were enumerated flow cytometrically employing the Stro-1 antibody, and clonally in the colony forming unit fibroblast (CFU-F) assay. Plasma levels of IGF-1 (ng/ml) and IL-6 (pg/ml) were measured by ELISA. SP-HSC in blood and bone marrow decreased with age but the quality of the surviving stem cells increased. MSC decreased non-significantly. IGF-1 levels (mean=30.7, SEM=2) decreased and IL-6 levels (mean=4.4, SEM=1) increased with age as did marrow fat (mean=1.2mmfat/g, SEM=0.04). There were no significant correlations between cytokine levels or fat and SP-HSC numbers. Stem cells appear to be progressively lost with aging and only the highest quality stem cells survive.

Initial clinical experience with Myxo-ETlogix mitral valve repair ring.

OBJECTIVE: Complexity of mitral valve repair for myxomatous disease has led to low adoption. We report initial experience with a new ring designed specifically for myxomatous disease, the Myxo-ETlogix (Edwards Lifesciences LLC, Irvine, Calif). METHODS: From March 15, 2006, through November 19, 2007, 129 patients underwent mitral valve surgery for pure myxomatous disease, and 124 valves (96.1%) were repaired. The Myxo-ETlogix ring was used in 100 cases and the Physio ring (Edwards) in 24. The Myxo-ETlogix design includes a 3-dimensional shape to reduce systolic anterior motion and a larger orifice to accommodate elongated leaflets and decrease need for sliding plasty. Direct mitral valve measurements were made. Sizing was based on A2 height, and choice of ring type was based on unresected leaflet heights. RESULTS: There was no operative mortality or lasting perioperative morbidity. The Myxo-ETlogix group had taller A2, P1, P2, and P3 leaflet segments than the Physio group (P < or = .003). Only 1 sliding plasty was performed for asymmetry in the Myxo-ETlogix group. Predischarge and follow-up echocardiograms (n = 338 in 124 patients) disclosed transient nonobstructive chordal systolic anterior motion in 3 echocardiograms in 3 patients. No patients had 2+ or greater mitral regurgitation. At discharge, 5.7% had 1+ mitral regurgitation; this proportion was 17.3% at last follow-up (mean 6.1 +/- 4.4 months). CONCLUSION: In initial experience with the Myxo-ETlogix ring, nonobstructive systolic anterior motion has been rare and obstructive systolic anterior motion not observed. Ongoing prospective echocardiographic and clinical studies will elucidate the role of this etiology-specific ring.

General and specific psychotherapy role induction with substance-abusing clients.

The present study examined the effects of general and specific psychotherapy role induction on return rates and attendance in psychotherapy for substance-abusing clients. The subjects were 111 of 129 consecutive applicants to a community outpatient drug treatment center. Following a standard intake interview, clients received either a general psychotherapy role induction or a drug treatment specific role induction, or were placed in one of two control conditions. Results indicated that clients who received role induction procedures were more likely than controls to return after the intake interview. Furthermore, clients who received the drug treatment specific role induction returned at a significantly higher rate than all other clients. Analysis of attendance rates after 3 months showed that role induction had no effect on continuation in treatment.

Pentostatin: an adenosine deaminase inhibitor for the treatment of hairy cell leukemia.

OBJECTIVE: To review the pharmacology, pharmacokinetics, adverse effects, and various dosage regimens of pentostatin, and to evaluate the role of pentostatin in the treatment of hairy cell leukemia (HCL). DATA IDENTIFICATION: Articles were identified via an English-language literature search of MEDLINE (1966-91) and an extensive search of bibliographies from identified articles. STUDY SELECTION: Human clinical trials and case reports were selected for evaluation. DATA EXTRACTION: The literature was assessed for quality, methodology, and outcome information. DATA SYNTHESIS: At dosages of 4 mg/m2 administered every other week for 6-9 months, pentostatin has been shown to successfully induce a complete response in 58-90 percent of patients and to produce a partial response in up to 30 percent of patients with HCL. The median time to achieve a response is 4.7 months. Long-term remissions of at least 14 months' duration have occurred in some patients. Compared with interferon alfa alone, total response rates are not significantly different when pentostatin and interferon alfa are used in combination. When dosed appropriately, pentostatin is generally well tolerated. Common adverse effects include nausea, vomiting, myelosuppression, fever, and infection. CONCLUSIONS: Pentostatin is a purine analog that inhibits adenosine deaminase, a key enzyme necessary for purine salvage. Pentostatin has received labeling approval for the treatment of HCL refractory to a minimum of three to six months of treatment with interferon alfa. Based on current data, pentostatin will be a useful addition to the therapeutic agents presently available to patients with HCL. Ongoing trials are evaluating the effectiveness of pentostatin as first-line therapy for patients with HCL.

Aminophylline for methotrexate-induced neurotoxicity.

Methotrexate, a mainstay treatment for children with acute lymphoblastic leukaemia, can cause neurotoxicity, with paralysis, seizures, somnolence, anorexia, and headaches. The pathophysiology of this reaction is unknown. It has been suggested that the anti-inflammatory effect of methotrexate in patients with arthritis is due to adenosine release brought on by inhibition of purine synthesis. Since adenosine is a central nervous system depressant, we wondered whether adenosine release in the central nervous system could account for some of the neurotoxicity due to methotrexate, and whether that toxicity could be lessened by displacement of adenosine from its receptor by aminophylline. 6 patients (age 3-16 years) who had methotrexate-induced neurotoxicity unresponsive to standard treatment received 2.5 mg/kg aminophylline. In addition, the concentration of adenosine in the cerebrospinal fluid (CSF) from 11 children completing a 24-h systemic methotrexate protocol was compared with that in 8 newly diagnosed patients and 12 who had not received any treatment for at least a week. 4 of 6 patients with toxic signs and symptoms attributed to methotrexate and unrelieved by steroids, epidural blood patch, promethazine, 5-hydroytryptamine antagonists, paracetamol, and narcotics, had complete resolution of neurotoxicity after or during a 1-h infusion of aminophylline; 2 others had a pronounced improvement but persistent nausea. CSF adenosine concentrations of patients receiving methotrexate, even when there was very slight or no toxicity, were greatly increased compared with control subjects (mean values of 217 and 51 nmol/L, median 175 and 52 nmol/L). Subacute methotrexate neurotoxicity may be mediated by adenosine and relieved by aminophylline.

The effect of vascular curvature on three-dimensional reconstruction of intravascular ultrasound images.

OBJECTIVE: To characterize the effect of vessel curvature on the geometric accuracy of conventional three-dimensional reconstruction (3DR) algorithms for intravascular ultrasound image data. BACKGROUND: A common method of 3DR for intravascular ultrasound image data involves geometric reassembly and volumetric interpolation of a spatially related sequence of tomographic cross sections generated by an ultrasound catheter withdrawn at a constant rate through a vascular segment of interest. The resulting 3DR is displayed as a straight segment, with inherent vascular curvature neglected. Most vascular structures, however, are not straight but curved to some degree. For this reason, vascular curvature may influence the accuracy of computer-generated 3DR. METHODS: We collected image data using three different intravascular ultrasound catheters (2.9 Fr, 4.3 Fr, 8.0 Fr) during a constant-rate pullback of 1 mm/sec through tubing of known diameter with imposed radii of curvature ranging from 2 to 10 cm. Image data were also collected from straight tubing. Image data were digitized at 1.0-mm intervals through a length of 25 mm. Two passes through each radius of curvature were performed with each intravascular ultrasound catheter. 3DR lumen volume for each radius of curvature was compared to that theoretically expected from a straight cylindrical segment. Differences between 3DR lumen volume of theoretical versus curved (actual) tubes were quantified as absolute percentage error and categorized as a function of curvature. Tubing deformation error was quantified by quantitative coronary angiography (QCA). RESULTS: Volumetric errors ranged from 1% to 35%, with an inverse relationship demonstrated between 3DR lumen volume and segmental radius of curvature. Higher curvatures (r < 6.0 cm) induced greater lumen volume error when compared to lower curvatures (r > 6.0 cm). This trend was exhibited for all three catheters and was shown to be independent of tubing deformation artifacts. QCA-determined percentage diameter stenosis indicated no deformation error as a function of curvature. Total volumetric error contributed by tubing deformation was estimated to be 0.05%. CONCLUSIONS: Catheter-dependent geometrical error arises in three-dimensionally reconstructed timed linear pullbacks of intravascular ultrasound images due in part to uniplanar vascular curvature. Three-dimensional reconstruction of timed linear pullbacks is robust for vessels with low radii of curvature; however, careful interpretation of three-dimensional reconstructions from timed linear pullbacks for higher radii of curvature is warranted. These data suggest that methods of spatially correct three-dimensional reconstruction of intravascular ultrasound images should be considered when more pronounced vascular curvature is present.

Cardiac memory: a mechanical and electrical phenomenon.

Alterations in repolarization following prolonged periods of ventricular pacing, termed "cardiac memory," have been well documented. Postpacing changes in cardiac function have also been noted in hypertrophic cardiomyopathy. This study was designed to evaluate the effects of ventricular pacing on postpacing diastolic function and its relationship to repolarization changes. Eight subjects (mean age, 76 yr) with permanent pacemakers were enrolled in this study. Each subject was evaluated at a fixed pacing rate with recording of electrocardiographic and echocardiographic data. Seven sets of measurements were performed in the same sequential pattern: 1) after 1 wk of atrial pacing, 2) within 10 min after initiation of atrioventricular sequential pacing (ventricular pacing), 3) within 10 min after termination of 1 h of ventricular pacing, 4) after 1 wk of ventricular pacing, and 5) within 10 min, at 1 h, and at 24 h after termination of ventricular pacing. All subjects had repolarization changes characteristic of cardiac memory only after 1 wk of ventricular pacing. Changes in repolarization parameters were accompanied by changes in peak left ventricular filling rate (dD/dt/D; P = 0.02) and isovolumic relaxation time (IVRT; P = 0.03) that at 24 h approached baseline values. Correlations existed between changes in the Q-T interval and IVRT (r = 0.53, P = 0.007) and between changes in T wave amplitude and dD/dt/D (r = 0.48, P = 0.018) after long-term ventricular pacing. Thus changes in both repolarization and diastolic function persist after cessation of ventricular pacing and lend support to the concept of electrical and mechanical cardiac memory.

Doppler catheter tip localization using color enhancement.

The objective of this research was to determine if the ultrasound emissions of the Doppler catheter can be used to locate its position in 3 dimensions by conventional echocardiography. A Doppler catheter has previously been shown to permit nonfluoroscopic retrograde catheterization of the aortic root and left ventricular chamber by using velocity waveform polarity for directional guidance. A significant difficulty in providing ultrasound catheter guidance, however, has been the inability to recognize the Doppler catheter tip, because each point at which a flexible catheter crosses the image plane can be misinterpreted as the catheter tip. Initial in vitro water bath trials were performed using the Doppler catheter attached to a standard velocimeter. Using a 5 MHz imaging transducer and color Doppler methods, the presence or absence of a banded color pattern which could demarcate the Doppler catheter tip was recorded at various angles in and out of the scanning plane. Using Doppler retrograde guidance and transesophageal echocardiography, color Doppler banded patterns, which could identify the Doppler catheter tip, were investigated in the dog aorta. In order to understand the physical mechanisms involved, a series of water bath trials were then conducted using the Doppler catheter attached to a velocimeter which was synchronized to the echo machine. Initial nonsynchronized water bath trials revealed distinct banded color patterns demarcating the Doppler catheter tip when it pointed in any direction within the beam width, except for a 40 degrees blind cone directly away from the imaging transducer.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo assessment of nonlinear myocardial deformation using finite element analysis and three-dimensional echocardiographic reconstruction.

In vitro data have shown that the myocardium exhibits nonlinear passive stress-strain relationship and a non-linear pressure-volume relationship. A finite element (FE) analysis and optimization algorithm was used on three-dimensional reconstructed left ventricular (LV) geometry using echocardiographic images, along with hemodynamic measurements, in seven closed-chest dogs to show a nonlinear stress-strain relationship in vivo. Our analysis included the computation of Poisson's ratio from the measured volumetric strain of the myocardium and a simulated pericardial pressure load ("equivalent pericardial pressure") applied to the epicardial surface of the reconstructed LV. LV geometry was reconstructed in three or four incremental time steps in diastasis and the myocardium was assumed to be homogeneous, isotropic, and linearly elastic during these short intervals in this initial study. Simultaneous LV chamber pressure and equivalent pericardial pressure were incorporated into the algorithm to predict actual LV expansion. Computations were performed iteratively at each interval to compute the optimized elastic modulus. By performing the FE analysis and optimization at each interval (a step-wise linear analysis approach), a linear relationship between the myocardial elastic modulus and LV chamber pressure was derived (r = .87 to .98). Such a linear relationship is equivalent to an exponential myocardial stress-strain relationship in vivo. Detailed measurement of nonhomogeneous regional deformation are becoming possible with the advent of sophisticated imaging techniques. The methodology described in this study, with appropriate modifications in the FE analysis and optimization algorithms, can be applied to assess the complex three-dimensional pressure-deformation characteristics in vivo.