Porcine Model Of Pulmonary Embolism Research Articles

TCT-739 Ultrasound-Enhanced Catheter Directed Thrombolysis in a Porcine Model of Pulmonary Embolism

TCT-739 Ultrasound-Enhanced Catheter Directed Thrombolysis in a Porcine Model of Pulmonary Embolism

Detection of Pulmonary Embolism Based on Reduced Changes in Radiographic Lung Density During Cardiac Beating Using Dynamic Flat-panel Detector: An Animal-based Study

To assess the capacity of dynamic flat-panel detector imaging without the use of contrast media to detect pulmonary embolism (PE) based on temporal changes in radiographic lung density during cardiac beating. Sequential chest radiographs of six pigs were acquired using a dynamic flat-panel detector system. A porcine model of PE was developed, and temporal changes in pixel values in the imaged lungs were analyzed during a whole cardiac cycle. Mean differences in temporal changes in pixel values between affected and unaffected lobes were assessed using the paired t test. To facilitate visual evaluation, temporal changes in pixel values were depicted using a colorimetric scale and were compared to the findings of contrast-enhanced images. Affected lobes exhibited a mean reduction of 49.6% in temporal changes in pixel values compared to unaffected lobes within the same animals, and a mean reduction of 41.3% compared to that before vessel blockage in the same lobe. All unaffected lobes exhibited significantly-increased changes in pixel values after vessel blockage (p < 0.01). In all PE models, there were color-deficient areas with shapes and locations that matched well with the perfusion defects confirmed in the corresponding contrast-enhanced images. Dynamic chest radiography enables the detection of perfusion defects in the lobe unit based on temporal changes in image density, even without the use of contrast media. Quantification and visualization techniques provide a better understanding of the circulation-induced changes depicted in dynamic chest radiographs.

Patient specific identification of the cardiac driver function in a cardiovascular system model

The cardiac muscle activation or driver function, is a major determinant of cardiovascular dynamics, and is often approximated by the ratio of the left ventricle pressure to the left ventricle volume. In an intensive care unit, the left ventricle pressure is usually never measured, and the left ventricle volume is only measured occasionally by echocardiography, so is not available real-time. This paper develops a method for identifying the driver function based on correlates with geometrical features in the aortic pressure waveform. The method is included in an overall cardiovascular modelling approach, and is clinically validated on a porcine model of pulmonary embolism. For validation a comparison is done between the optimized parameters for a baseline model, which uses the direct measurements of the left ventricle pressure and volume, and the optimized parameters from the approximated driver function. The parameters do not significantly change between the two approaches thus showing that the patient specific approach to identifying the driver function is valid, and has potential clinically.

Model-based identification of PEEP titrations during different volemic levels

A cardiovascular system (CVS) model has previously been validated in simulated cardiac and circulatory disease states. It has also been shown to accurately capture all main hemodynamic trends in a porcine model of pulmonary embolism. In this research, a slightly extended CVS model and parameter identification process are presented and validated in a porcine experiment of positive end-expiratory pressure (PEEP) titrations at different volemic levels. The model is extended to more physiologically represent the separation of venous and arterial circulation. Errors for the identified model are within 5% when re-simulated and compared to clinical data. All identified parameter trends match clinically expected changes. This work represents another clinical validation of the underlying fundamental CVS model, and the methods and approach of using them for cardiovascular diagnosis in critical care.

139 Right ventricular diastolic function in acute pulmonary embolism

Background: The effects of acute pulmonary embolism (PE) on right ventricular (RV) diastolic function may be one of the determinants of right heart failure. We analysed the parameters of RV diastolic function in a porcine model of PE by the use of phase plane (PP) analysis. In the PP method, a periodic function is plotted such that the function, RV pressure (P), is the abscissa and its time derivative (dP/dt) is the ordinate. Methods: In six anaesthetised open chest pigs, RV pressure-volume (PV) loops were obtained by the conductance catheter technique. Measurements were realised in basal conditions, and repeated 1 hour after injection of coagulated autologous blood clots (0.3g/kg) in the superior vena cava. PV loops and PP loops were constructed with pressure and volume signals. The parameters of RV diastolic function were calculated from the PV and PP loops. Results: End-diastolic pressure and end-diastolic volume increased respectively from 3.40 ± 2.71 to 6.46 ± 2.36 mmHg (mean ± SD, p < 0.05) and from 60.73 ± 9.65 to 80.45 ± 3.72 ml (mean ± SD, p < 0.05), with no significant change in RV compliance (0,19 ±0.14 and 0.19 ± 0.10 ml/mmHg, mean ± SD). RV peak negative dP/dt extended from 0.39 ± 0.08 to 0.65 ± 0.01 mmHg/msec (mean ± SD, p < 0.01). Monoexponential decay time constant (Tau) did not show significant variation (37.85 ± 6.90 to 41.22 ± 13.98 msec, mean ± SD). The RV relaxation curve in the PP graph was nonlinear and was fitted with a quadratic function (dP/dt = A P2+B P+ dP/dt°). The curvilinearity coefficient (A) and the intercept (dP/dt°) did not change significantly but the second constant (B) significantly decreased from -40.30 ± 13.50 to -56.72 ± 11.60 sec-1 (mean ± SD, p < 0.01). Conclusions: As assessed by PP analysis, acute RV pressure overload by PE induces modifications in RV diastolic function. The right ventricle dilates and its diastolic filling pressure increases. Relaxation time constant calculated with monoexponential decay method, that considers linear relaxation of the ventricle, does not significantly changed. The relaxation curve in the PP graph, however, appears modified, as shown by the higher second constant of the fitted quadratic function. This reflects that the relaxation is non-uniform and that the non-uniformity is modified in acute PE in a such way that Tau would increase in early relaxation while it would decrease in late relaxation.

Detection of Lung Perfusion Abnormalities Using Computed Tomography in a Porcine Model of Pulmonary Embolism

The purpose of this study was to identify perfusion defects of the lung using computed tomography (CT). A balloon catheter was placed in a lobar pulmonary artery of six anesthetized, ventilated, juvenile pigs to simulate occlusive segmental embolus. Contrast medium was injected via a central venous catheter at rates of 1.5, 3, 4.5, and 9 ml/s in each pig. A 40-second single-level cine CT was acquired distal to the inflated balloon during suspended inspiration. Three computer-manipulated images (time to maximal enhancement, change in maximal attenuation, maximal contrast minus precontrast subtraction) were generated using custom software and compared with the unmodified maximal enhancement and precontrast images. Two independent observers identified perfusion defects and scored the level of confidence (5-point scale) on all five images. Regions of interest were drawn in perfused and nonperfused lung and time-attenuation curves were generated. Perfusion defects were accurately (99.8 +/- 0.3%) and confidently (4.5 +/- 0.6) detected and there was excellent interobserver agreement (Kappa 0.99 +/- 0.02) on all computer-manipulated images. There was a significant increase in confidence (p < 0.05) between contrast medium injection rates of 1.5 and 9 ml/s. A linear relationship exists (r = 0.88) between injection rate and change in maximal attenuation. In conclusion, perfusion defects of the lung are seen using computer-manipulated CT images.

Pulmonary perfusion: qualitative assessment with dynamic contrast-enhanced MRI using ultra-short TE and inversion recovery turbo FLASH.

The accurate assessment of pulmonary perfusion is especially important in the evaluation of patients with suspected pulmonary embolism, a common and potentially lethal disorder that can be treated by aggressive anticoagulation. In this study, we demonstrate for the first time the use of MR to image pulmonary perfusion in humans by using dynamic imaging after contrast administration. The technique, which uses an inversion recovery turbo FLASH sequence with ultrashort TE (1.4 ms) and 1-s temporal resolution, was tested in a series of eight healthy subjects and in a porcine model of pulmonary embolism. After the administration of gadopentetate dimeglumine in humans and animal models, there was serial enhancement of the systemic veins, right atrium, right ventricle, and pulmonary arteries. The pulmonary arterial tree was visualized beyond the segmental branches, followed by a gradual diffuse increase in signal intensity of the lung parenchyma over a period of 4.0-7.0 s. Pulmonary circulation times ranged from 3.0-3.4 s. Whereas a high dose (20 or 40 ml) of contrast agent tended to produce the most intense parenchymal enhancement, a low dose (5 ml) was best for showing recirculation. In the animal model, a perfusion defect due to a pulmonary embolus was clearly shown and confirmed by cine angiography. It is concluded that MRI of lung perfusion is feasible. With further development, perfusion MRI could eventually have a significant clinical role in the diagnostic evaluation of pulmonary embolism.