Anna Bjällmark

Ultrasonographic strain imaging is superior to conventional non-invasive measures of vascular stiffness in the detection of age-dependent differences in the mechanical properties of the common carotid artery

AIMSnElastic properties of large arteries have been shown to deteriorate with age and in the presence of atherosclerotic vascular disease. In this study, the performance of ultrasonographic strain measurements was compared with conventional measures of vascular stiffness in the detection of age-dependent differences in the elastic properties of the common carotid artery (CCA).nnnMETHODS AND RESULTSnIn 10 younger (25-28 years, four women) and 10 older (50-59 years, four women) healthy individuals, global and regional circumferential, and radial strain variables were measured in the short-axis view of the right CCA using ultrasonographic two-dimensional (2D) strain imaging with recently introduced speckle tracking technique. Conventional elasticity variables, elastic modulus (E(p)), and beta stiffness index, were calculated using M-mode sonography and non-invasive blood pressure measurements. Global and regional circumferential systolic strain and strain rate values were significantly higher (P < 0.01 for regional late systolic strain rate, P < 0.001 otherwise) in the younger individuals, whereas the values of conventional stiffness variables in the same group were lower (P < 0.05). Among all strain and conventional stiffness variables, principal component analysis and its regression extension identified only circumferential systolic strain variables as contributing significantly to the observed discrimination between the younger and older age groups.nnnCONCLUSIONnUltrasonographic 2D-strain imaging is a sensitive method for the assessment of elastic properties in the CCA, being in this respect superior to the conventional measures of vascular stiffness. The method has potential to become a valuable non-invasive tool in the detection of early atherosclerotic vascular changes.

Shear wave elastography plaque characterization with mechanical testing validation: A phantom study

Determining plaque vulnerability is critical when selecting the most suitable treatment for patients with atherosclerotic plaque. Currently, clinical non-invasive ultrasound-based methods for plaque characterization are limited to visual assessment of plaque morphology and new quantitative methods are needed. In this study, shear wave elastography (SWE) was used to characterize hard and soft plaque mimicking inclusions in six common carotid artery phantoms by using phase velocity analysis in static and dynamic environments. The results were validated with mechanical tensile testing. In the static environment, SWE measured a mean shear modulus of 5.8 ± 0.3 kPa and 106.2 ± 17.2 kPa versus 3.3 ± 0.5 Pa and 98.3 ± 3.4 kPa measured by mechanical testing in the soft and hard plaques respectively. Furthermore, it was possible to measure the plaques shear moduli throughout a simulated cardiac cycle. The results show good agreement between SWE and mechanical testing and indicate the possibility for in vivo arterial plaque characterization using SWE.

Arterial Stiffness Estimation by Shear Wave Elastography: Validation in Phantoms with Mechanical Testing.

Arterial stiffness is an independent risk factor found to correlate with a wide range of cardiovascular diseases. It has been suggested that shear wave elastography (SWE) can be used to quantitatively measure local arterial shear modulus, but an accuracy assessment of the technique for arterial applications has not yet been performed. In this study, the influence of confined geometry on shear modulus estimation, by both group and phase velocity analysis, was assessed, and the accuracy of SWE in comparison with mechanical testing was measured in nine pressurized arterial phantoms. The results indicated that group velocity with an infinite medium assumption estimated shear modulus values incorrectly in comparison with mechanical testing in arterial phantoms (6.7 ± 0.0 kPa from group velocity and 30.5 ± 0.4 kPa from mechanical testing). To the contrary, SWE measurements based on phase velocity analysis (30.6 ± 3.2 kPa) were in good agreement with mechanical testing, with a relative error between the two techniques of 8.8 ± 6.0% in the shear modulus range evaluated (40-100 kPa). SWE by phase velocity analysis was validated to accurately measure stiffness in arterial phantoms.

Closed-loop real-time simulation model of hemodynamics and oxygen transport in the cardiovascular system

BackgroundComputer technology enables realistic simulation of cardiovascular physiology. The increasing number of clinical surgical and medical treatment options imposes a need for better understanding of patient-specific pathology and outcome prediction.MethodsA distributed lumped parameter real-time closed-loop model with 26 vascular segments, cardiac modelling with time-varying elastance functions and gradually opening and closing valves, the pericardium, intrathoracic pressure, the atrial and ventricular septum, various pathological states and including oxygen transport has been developed.ResultsModel output is pressure, volume, flow and oxygen saturation from every cardiac and vascular compartment. The model produces relevant clinical output and validation of quantitative data in normal physiology and qualitative directions in simulation of pathological states show good agreement with published data.ConclusionThe results show that it is possible to build a clinically relevant real-time computer simulation model of the normal adult cardiovascular system. It is suggested that understanding qualitative interaction between physiological parameters in health and disease may be improved by using the model, although further model development and validation is needed for quantitative patient-specific outcome prediction.

Evaluation of tissue Doppler-based velocity and deformation imaging: a phantom study of ultrasound systems

AIMSnThe objective of this study was to test the accuracy and diagnostic interchangeability of tissue Doppler-based displacement, velocity, strain, and strain rate measurements in commercially used ultrasound (US) systems.nnnMETHODS AND RESULTSnUsing an in-house made phantom, four different US scanner models were evaluated. Two different scanners of the same model were tested, and one scanner acquisition was tested twice with two generations of the same workstation giving six test results in total. The scanners were in active clinical use and are subject to regular maintenance checks. There were three displacement and four velocity results that stood out from the rest and could be regarded as accurate and interchangeable. Among the deformation measurements, three acceptable strain results were found while there were no acceptable strain rate results. Furthermore, the study showed that measurements from scanners of the same model, same acquisition post-processed on different workstations and repeated measurements from the same scanner, can yield disparate results.nnnCONCLUSIONnMeasurements that are accurate and of interchangeable use can be found for displacement and velocity measurements, but are less likely to be found for strain and strain rate measurements. It is strongly recommended that the ability of each individual US scanner to measure displacement, velocity, strain, and strain rate is evaluated before it is introduced into clinical practice, and it must always be evaluated together with the workstation the scanner is intended to be used in conjunction with.

Recirculation during veno-venous extra-corporeal membrane oxygenation – a simulation study

Purpose Veno-venous ECMO is indicated in reversible life-threatening respiratory failure without life-threatening circulatory failure. Recirculation of oxygenated blood in the ECMO circuit decreases efficiency of patient oxygen delivery but is difficult to measure. We seek to identify and quantify some of the factors responsible for recirculation in a simulation model and compare with clinical data. Methods A closed-loop real-time simulation model of the cardiovascular system has been developed. ECMO is simulated with a fixed flow pump 0 to 5 l/min with various cannulation sites – 1) right atrium to inferior vena cava, 2) inferior vena cava to right atrium, and 3) superior+inferior vena cava to right atrium. Simulations are compared to data from a retrospective cohort of 11 consecutive adult veno-venous ECMO patients in our department. Results Recirculation increases with increasing ECMO-flow, decreases with increasing cardiac output, and is highly dependent on choice of cannulation sites. A more peripheral drainage site decreases recirculation substantially. Conclusions Simulations suggest that recirculation is a significant clinical problem in veno-venous ECMO in agreement with clinical data. Due to the difficulties in measuring recirculation and interpretation of the venous oxygen saturation in the ECMO drainage blood, flow settings and cannula positioning should rather be optimized with help of arterial oxygenation parameters. Simulation may be useful in quantification and understanding of recirculation in VV-ECMO.

Wave intensity wall analysis: a novel noninvasive method to measure wave intensity

Wave intensity analysis is a concept providing information about the interaction of the heart and the vascular system. Originally, the technique was invasive. Since then new noninvasive methods have been developed. A recently developed ultrasound technique to estimate tissue motion and deformation is speckle-tracking echocardiography. Speckle tracking-based techniques allow for accurate measurement of movement and deformation variables in the arterial wall in both the radial and the longitudinal direction. The aim of this study was to test if speckle tracking-derived deformation data could be used as input for wave intensity calculations. The new concept was to approximate changes of flow and pressure by deformation changes of the arterial wall in longitudinal and radial directions. Flow changes (dU/dt) were approximated by strain rate (sr, 1/s) of the arterial wall in the longitudinal direction, whereas pressure changes (dP/dt) were approximated by sign reversed strain rate (1/s) in the arterial wall in the radial direction. To validate the new concept, a comparison between the newly developed Wave Intensity Wall Analysis (WIWA) algorithm and a commonly used and validated wave intensity system (SSD-5500, Aloka, Tokyo, Japan) was performed. The studied population consisted of ten healthy individuals (three women, seven men) and ten patients (all men) with coronary artery disease. The present validation study indicates that the mechanical properties of the arterial wall, as measured by a speckle tracking-based technique are a possible input for wave intensity calculations. The study demonstrates good visual agreement between the two systems and the time interval between the two positive peaks (W1–W2) measured by the Aloka system and the WIWA system correlated for the total group (r = 0.595, P < 0.001). The correlation for the diseased subgroup was r = 0.797, P < 0.001 and for the healthy subgroup no significant correlation was found (P > 0.05). The results of the study indicate that the mechanical properties of the arterial wall could be used as input for wave intensity calculations. The WIWA concept is a promising new method that potentially provides several advantages over earlier wave intensity methods, but it still has limitations and needs further refinement and larger studies to find the optimal clinical use.

State diagrams of the heart--a new approach to describing cardiac mechanics.

BackgroundCardiac time intervals have been described as a measure of cardiac performance, where prolongation, shortening and delay of the different time intervals have been evaluated as markers of cardiac dysfunction. A relatively recently developed method with improved ability to measure cardiac events is Tissue Doppler Imaging (TDI), allowing accurate measurement of myocardial movements.MethodsWe propose the state diagram of the heart as a new visualization tool for cardiac time intervals, presenting comparative, normalized data of systolic and diastolic performance, providing a more complete overview of cardiac function. This study aimed to test the feasibility of the state diagram method by presenting examples demonstrating its potential use in the clinical setting and by performing a clinical study, which included a comparison of the state diagram method with established echocardiography methods (E/E ratio, LVEF and WMSI). The population in the clinical study consisted of seven patients with non ST-elevation myocardial infarction (NSTEMI) and seven control subjects, individually matched according to age and gender. The state diagram of the heart was generated from TDI curves from seven positions in the myocardium, visualizing the inter- and intraventricular function of the heart by displaying the cardiac phases.ResultsThe clinical examples demonstrated that the state diagram allows for an intuitive visualization of pathological patterns as ischemia and dyssynchrony. Further, significant differences in percentage duration between the control group and the NSTEMI group were found in eight of the totally twenty phases (10 phases for each ventricle), e.g. in the transition phases (Pre-Ejection and Post-Ejection). These phases were significantly longer (> 2.18%) for the NSTEMI group than for the control group (p < 0.05). No significant differences between the groups were found for the established echocardiography methods.ConclusionThe test results clearly indicate that the state diagram has potential to be an efficient tool for visualization of cardiac dysfunction and for detection of NSTEMI.

Venous Cannula Positioning in Arterial Deoxygenation During Veno-Arterial Extracorporeal Membrane Oxygenation-A Simulation Study and Case Report.

Abstract Venoarterial extracorporeal membrane oxygenation (VA‐ECMO) is indicated in reversible life‐threatening circulatory failure with or without respiratory failure. Arterial desaturation in the upper body is frequently seen in patients with peripheral arterial cannulation and severe respiratory failure. The importance of venous cannula positioning was explored in a computer simulation model and a clinical case was described. A closed‐loop real‐time simulation model has been developed including vascular segments, the heart with valves and pericardium. ECMO was simulated with a fixed flow pump and a selection of clinically relevant venous cannulation sites. A clinical case with no tidal volumes due to pneumonia and an arterial saturation of below 60% in the right hand despite VA‐ECMO flow of 4 L/min was described. The case was compared with simulation data. Changing the venous cannulation site from the inferior to the superior caval vein increased arterial saturation in the right arm from below 60% to above 80% in the patient and from 64 to 81% in the simulation model without changing ECMO flow. The patient survived, was extubated and showed no signs of hypoxic damage. We conclude that venous drainage from the superior caval vein improves upper body arterial saturation during veno‐arterial ECMO as compared with drainage solely from the inferior caval vein in patients with respiratory failure. The results from the simulation model are in agreement with the clinical scenario.

Left ventricular mechanical dyssynchrony in patients with different stages of chronic kidney disease and the effects of hemodialysis

Left ventricular (LV) dyssynchrony is a known cause of mortality in patients with heart failure and may possibly play a similar role in patients with chronic kidney disease (CKD) in whom sudden death is one of the most common and as yet not fully explained cause of death. LV synchronicity and its relationship with increased volume load and various biomarkers was analyzed in 145 patients including 53 patients with CKD stages 3 and 4 and in 92 CKD stage 5 patients undergoing hemodialysis (HD) or peritoneal dialysis (PD) using color tissue Doppler imaging and tissue synchronization imaging. The HD patients were evaluated both before and after a single HD session. LV dyssynchrony was defined as a regional difference in time to peak systolic myocardial velocity, between 12 LV segmentsu2009>u2009105u2009milliseconds. LV dyssynchrony was present in 54% of the patients with no difference between CKD 3 and 4 (58%), HD (48%), and PD (51%). LV dyssynchrony was independently associated with LV mass index and increased estimation of LV end‐diastolic pressure. A single HD session resulted in significant changes in LV synchronicity variables—with improvement in 50% of the patients—especially in patients with higher myocardial systolic velocities and lower LV mass index. Abnormalities in LV synchronicity are highly prevalent in CKD patients already prior to dialysis treatment and are associated with LV hypertrophy, LV dysfunction and load conditions, underlining the importance of volume status for LV synchronicity in CKD patients.