Showing papers by "Marek Belohlavek published in 2012"

Cerebral blood flow in Alzheimer’s disease

Abstract: BACKGROUND Alzheimer's disease (AD) dementia is a consequence of heterogeneous and complex interactions of age-related neurodegeneration and vascular-associated pathologies. Evidence has accumulated that there is increased atherosclerosis/arteriosclerosis of the intracranial arteries in AD and that this may be additive or synergistic with respect to the generation of hypoxia/ischemia and cognitive dysfunction. The effectiveness of pharmacologic therapies and lifestyle modification in reducing cardiovascular disease has prompted a reconsideration of the roles that cardiovascular disease and cerebrovascular function play in the pathogenesis of dementia. METHODS Using two-dimensional phase-contrast magnetic resonance imaging, we quantified cerebral blood flow within the internal carotid, basilar, and middle cerebral arteries in a group of individuals with mild to moderate AD (n = 8) and compared the results with those from a group of age-matched nondemented control (NDC) subjects (n = 9). Clinical and psychometric testing was performed on all individuals, as well as obtaining their magnetic resonance imaging-based hippocampal volumes. RESULTS Our experiments reveal that total cerebral blood flow was 20% lower in the AD group than in the NDC group, and that these values were directly correlated with pulse pressure and cognitive measures. The AD group had a significantly lower pulse pressure (mean AD 48, mean NDC 71; P = 0.0004). A significant group difference was also observed in their hippocampal volumes. Composite z-scores for clinical, psychometric, hippocampal volume, and hemodynamic data differed between the AD and NDC subjects, with values in the former being significantly lower (t = 12.00, df = 1, P = 0.001) than in the latter. CONCLUSION These results indicate an association between brain hypoperfusion and the dementia of AD. Cardiovascular disease combined with brain hypoperfusion may participate in the pathogenesis/pathophysiology of neurodegenerative diseases. Future longitudinal and larger-scale confirmatory investigations measuring multidomain parameters are warranted.

New echocardiographic techniques for evaluation of left atrial mechanics.

Abstract: Until recently the left atrium had been subordinate to the left ventricle, but cardiologists now recognize that left atrial (LA) function is indispensable to normal circulatory performance. Transthoracic two-dimensional (2D) and Doppler echocardiography can elucidate parameters of LA function non-invasively. Yet, with the advent of 2D speckle-tracking echocardiography, we are able to detect early LA dysfunction even before structural changes occur. This is pivotal in some common disease states, such as atrial fibrillation, hypertension, and heart failure, in which LA deformation parameters can influence clinical management. However, a unique standardized technique to investigate LA deformation needs to be validated.

Vortex formation time: an emerging echocardiographic index of left ventricular filling efficiency?

Abstract: ARTICLE The mere existence of the formation number is intriguing since it hints at the possibility that nature uses this time scale for some evolutionary incentives such as optimum ejection of blood from the left atrium to the heart's left ventricle.—Gharib et al .1 About 500 years ago, Leonardo da Vinci conducted a haemodynamic study of the sinus of Valsalva in which he deduced and explained formation of a blood flow vortex.2 Fast forwarding to the present, Gharib et al .1 used an experimental arrangement of a piston producing a wide range of jets and vortex rings alongside those jets by pushing columns of fluid of length L through an orifice with diameter D . They referred to the length-to-diameter ratio, i.e. L / D , as the formation number . While settings with low L / D generated merely a single and rather weak vortex ring, settings with large L / D resulted in a vortex ring that could no longer grow and was followed by a less-efficient fluid transport by a trailing jet.3 The maximum growth of the vortex ring without a trailing jet was observed when the L / D ratio was within a limited value range of 3.6–4.6 for an otherwise wide variety of flow conditions.1 Because …

Weighted Least-Squares Finite Element Method for Cardiac Blood Flow Simulation with Echocardiographic Data

Abstract: As both fluid flow measurement techniques and computer simulation methods continue to improve, there is a growing need for numerical simulation approaches that can assimilate experimental data into the simulation in a flexible and mathematically consistent manner. The problem of interest here is the simulation of blood flow in the left ventricle with the assimilation of experimental data provided by ultrasound imaging of microbubbles in the blood. The weighted least-squares finite element method is used because it allows data to be assimilated in a very flexible manner so that accurate measurements are more closely matched with the numerical solution than less accurate data. This approach is applied to two different test problems: a flexible flap that is displaced by a jet of fluid and blood flow in the porcine left ventricle. By adjusting how closely the simulation matches the experimental data, one can observe potential inaccuracies in the model because the simulation without experimental data differs significantly from the simulation with the data. Additionally, the assimilation of experimental data can help the simulation capture certain small effects that are present in the experiment, but not modeled directly in the simulation.

Accurate guidance of a catheter by ultrasound imaging and identification of a catheter tip by pulsed-wave Doppler.

Abstract: Background: With the advent of numerous minimally invasive medical procedures, accurate catheter guidance has become imperative. We introduce and test an approach for catheter guidance by ultrasound imaging and pulsed-wave (PW) Doppler. Methods: A steerable catheter is fitted with a small piezoelectric crystal at its tip that actively transmits signals driven by a function generator. We call this an active-tip (AT) catheter. In a water tank, we immersed a “target” crystal and a rectangular matrix of four “reference” crystals. Two-dimensional (2D) ultrasound imaging was used for initial guidance and visualization of the catheter shaft, and then PW Doppler mode was used to identify the AT catheter tip and guide it to the simulated target that was also visible in the 2D ultrasound image. Ten guiding trials were performed from random initial positions of the AT catheter, each starting at approximately 8 cm from the target. Results: After the ten navigational trials, the average final distance of the catheter tip from the target was 2.4 ± 1.2 mm, and the range of distances from the trials was from a minimum of 1.0 mm to a maximum of 4.5 mm. Conclusions: Although early in the development process, these quantitative in vitro results show promise for catheter guidance with ultrasound imaging and tip identification by PW Doppler. (PACE 2012; 35:44–50)

Shape-based analysis of right ventricular dysfunction associated with acute pulmonary embolism

Abstract: Acute pulmonary embolism (APE) is known as one of the major causes of sudden death. However, high level of mortality caused by APE can be reduced, if detected in early stages of development. Hence, biomarkers capable of early detection of APE are of utmost importance. This study investigates how APE affects the biomechanics of the cardiac right ventricle (RV), taking one step towards developing functional biomarkers for early diagnosis and determination of prognosis of APE. To that end, we conducted a pilot study in pigs, which revealed the following major changes due to the severe RV afterload caused by APE: (1) waving paradoxical motion of the RV inner boundary, (2) decrease in local curvature of the septum, (3) lower positive correlation between the movement of inner boundaries of the septal and free walls of the RV, (4) slower blood ejection by the RV, and (5) discontinuous movement observed particularly in the middle of the RV septal wall.

Post-systolic shortening: a functional window into ischemic memory?

Abstract: The heart's memory eliminates the bad and magnifies the good; and thanks to this artifice we manage to endure the burdens of the past.—Gabriel Garcia Marquez ([1][1]) Myocardial post-systolic shortening is characterized by a large variability in both duration and magnitude. Although typically

Detection of progressive myocardial tissue injury by ultrasonic integrated backscatter immediately after coronary reperfusion.

Abstract: Myocardial reperfusion following ischemia may paradoxically cause additional injury, including microvascular damage and edema. These structural alterations augment tissue echogenicity, which is measurable by ultrasonic integrated backscatter (IB). We sought to characterize alterations in myocardial IB in an ischemic and reperfused region of the rat heart. Myocardial IB of the regions of interest in 12 adult male Sprague-Dawley rats was studied at baseline, during ischemia, and chronologically after coronary reopening, using an ultrasound frequency of 8 MHz. IB did not significantly change between baseline and ischemia. However, within 1 min of reperfusion, IB significantly increased and continued to increase until 10 min of reperfusion, when a plateau was reached. Areas of high echogenicity were comparable to infarcted areas on gross pathologic slices and had edema with extravasation of red blood cells. Myocardial reperfusion following ischemia significantly augments tissue echogenicity. A continuing increase of IB suggests a rapid progression of reperfusion injury.