Effect of Transmural Differences in Excitation-Contraction Delay and Contraction Velocity on Left Ventricle Isovolumic Contraction: A Simulation Study.

Recent studies have shown that left ventricle (LV) exhibits considerable transmural differences in active mechanical properties induced by transmural differences in electrical activity, excitation-contraction coupling, and contractile properties of individual myocytes. It was shown that the time between electrical and mechanical activation of myocytes (electromechanical delay: EMD) decreases from subendocardium to subepicardium and, on the contrary, the myocyte shortening velocity (MSV) increases in the same direction. To investigate the physiological importance of this inhomogeneity, we developed a new finite element model of LV incorporating the observed transmural gradients in EMD and MSV. Comparative simulations with the model showed that when EMD or MSV or both were set constant across the LV wall, the LV contractility during isovolumic contraction (IVC) decreased significantly ((dp/dt)max⁡  was reduced by 2 to 38% and IVC was prolonged by 18 to 73%). This was accompanied by an increase of transmural differences in wall stress. These results suggest that the transmural differences in EMD and MSV play an important role in physiological contractility of LV by synchronising the contraction of individual layers of ventricular wall during the systole. Reduction or enhancement of these differences may therefore impair the function of LV and contribute to heart failure.

Impact of isotropic constitutive descriptions on the predicted peak wall stress in abdominal aortic aneurysms.

Biomechanics-based assessment of Abdominal Aortic Aneurysm (AAA) rupture risk has gained considerable scientific and clinical momentum. However, computation of peak wall stress (PWS) using state-of-the-art finite element models is time demanding. This study investigates which features of the constitutive description of AAA wall are decisive for achieving acceptable stress predictions in it. Influence of five different isotropic constitutive descriptions of AAA wall is tested; models reflect realistic non-linear, artificially stiff non-linear, or artificially stiff pseudo-linear constitutive descriptions of AAA wall. Influence of the AAA wall model is tested on idealized (n=4) and patient-specific (n=16) AAA geometries. Wall stress computations consider a (hypothetical) load-free configuration and include residual stresses homogenizing the stresses across the wall. Wall stress differences amongst the different descriptions were statistically analyzed. When the qualitatively similar non-linear response of the AAA wall with low initial stiffness and subsequent strain stiffening was taken into consideration, wall stress (and PWS) predictions did not change significantly. Keeping this non-linear feature when using an artificially stiff wall can save up to 30% of the computational time, without significant change in PWS. In contrast, a stiff pseudo-linear elastic model may underestimate the PWS and is not reliable for AAA wall stress computations.

Structure-based constitutive model can accurately predict planar biaxial properties of aortic wall tissue.

Structure-based constitutive models might help in exploring mechanisms by which arterial wall histology is linked to wall mechanics. This study aims to validate a recently proposed structure-based constitutive model. Specifically, the model's ability to predict mechanical biaxial response of porcine aortic tissue with predefined collagen structure was tested. Histological slices from porcine thoracic aorta wall (n=9) were automatically processed to quantify the collagen fiber organization, and mechanical testing identified the non-linear properties of the wall samples (n=18) over a wide range of biaxial stretches. Histological and mechanical experimental data were used to identify the model parameters of a recently proposed multi-scale constitutive description for arterial layers. The model predictive capability was tested with respect to interpolation and extrapolation. Collagen in the media was predominantly aligned in circumferential direction (planar von Mises distribution with concentration parameter bM=1.03 ± 0.23), and its coherence decreased gradually from the luminal to the abluminal tissue layers (inner media, b=1.54 ± 0.40; outer media, b=0.72 ± 0.20). In contrast, the collagen in the adventitia was aligned almost isotropically (bA=0.27 ± 0.11), and no features, such as families of coherent fibers, were identified. The applied constitutive model captured the aorta biaxial properties accurately (coefficient of determination R(2)=0.95 ± 0.03) over the entire range of biaxial deformations and with physically meaningful model parameters. Good predictive properties, well outside the parameter identification space, were observed (R(2)=0.92 ± 0.04). Multi-scale constitutive models equipped with realistic micro-histological data can predict macroscopic non-linear aorta wall properties. Collagen largely defines already low strain properties of media, which explains the origin of wall anisotropy seen at this strain level. The structure and mechanical properties of adventitia are well designed to protect the media from axial and circumferential overloads.

The impact of intraluminal thrombus failure on the mechanical stress in the wall of abdominal aortic aneurysms.

OBJECTIVES: The role of the intraluminal thrombus (ILT) in abdominal aortic aneurysm (AAA) rupture is controversial, and it is still not clear if an ILT increases or decreases AAA rupture risk. Specifically, signs of bleeding in the ILT are considered to increase AAA rupture risk. To further explore this hypothesis, intact AAAs (n = 4) with clear signs of fissures in the ILT, identified by computed tomography angiography (CTA) were investigated. METHODS: Two different cases of ILT fissuring were investigated, where (1) ILT fissures were extracted directly from the CTA data and (2) a hypothetical fissure was introduced in the otherwise-intact ILT tissue. Wall stress distributions were predicted based on detailed Finite Element (FE) models. RESULTS: ILT fissures extracted from CTA data locally increase the mechanical stress in the underlying wall by up to 30%. The largest impact on wall stress was observed if the ILT crack reaches the aneurysm wall, or if it involves large parts of the ILT. By contrast, a concentric failure in the medial ILT, which does not reach the aneurysm wall, has almost no impact on wall stress distribution. Hypothetical ILT fissures that connect the lumen with the wall cause a twofold increase of the stress in the underlying wall. CONCLUSIONS: ILT fissures increase the stress in the underlying wall, whereas regions other than that remain unaffected. If ILT fissures reach the wall or involve large parts of the ILT, the resulting increase in wall stress could possibly cause AAA rupture.

Phalangeal quantitative ultrasound measurements in former pre-term children aged 9-11 years.

The objective of this study was to compare phalangeal ultrasound values in 38 former pre-term children, aged 9-11 years, with 50 age-matched term controls. Skeletal status was evaluated using phalangeal quantitative ultrasound measurements (QUS) by DBM Sonic 1200 (IGEA, Carpi, Italy) which measures the amplitude dependent speed of sound (Ad-SoS, m s(-1)). There were no significant differences in values of Ad-SoS, weight and height between patients and controls irrespective of birth weight or prematurity. In conclusion, phalangeal ultrasound measurements performed in prematurely born infants show that at the age of 9-11 years their bone status does not differ from children born at term.

[Immunologic laboratory findings in relatives of patients with common variable immunodeficiency]. / Laboratorní imunologické nálezy u príbuzných nemocných s bezným variabilním imunodeficitem.

A statistically significant increase of selective IgA deficiency was found evaluating 52 first degree relatives of 15 patients with common variable immunodeficiency, 4/5 of these cases were observed in the children of our patients. In addition to this decreased mean serum IgM level and increase of frequency of antithyroid autoantibodies compared to control subjects were observed. An excess of rheumatoid factor or antinuclear antibodies as not observed.

Infant morbidity and mortality in a region of ecological disaster.

Infant morbidity and mortality in the Upper Silesian Industrial Region (USIR) are indices of ecological disaster. In the most polluted region of such towns as Bytom, Chorzów and Zabrze, the infant mortality rate is very high and increasing. Indices of infant morbidity were higher in Katowice district than in the rest of Poland. Low birth weight (below 2,500 g) depends on the degree of pollution and influences the infant mortality rate. Most parents of children who died in the first year of life have been resident for at least 15 years. In Zabrze in recent years the percentage of congenital defects as the main cause of infant mortality is increasing.

Biochemical changes in sows after eleven or more farrowings.

The animals examined were 30 sows after eleven or more farrowings (pluriparous sows) and 26 primiparous sows. The pluriparous animals were 75.1 months old on the average and had farrowed an average of 13.23 litters. The mean age of the primiparous sows was 12.8 months. The blood sera of pluriparous sows had higher concentrations of total protein and urea and lower levels of 11-hydroxycorticosteroids (11-OHCS) and lower aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase activities than those of primiparous sows. The pluriparous sows showed mild hypoglycaemia and hypocholesterolaemia. When insulin was injected i.m. in the dose of 1 I.U. per kg body mass, a decrease in blood serum glucose, total protein and potassium levels was recorded 60 min later in both pluriparous and primiparous sows; a significant rise in 11-OHCS concentration occurred only in the primiparous sows. It was concluded that the response of the hypothalamo-pituitary-adrenal axis in pluriparous sows to an insulin load is reduced. Studies of pluriparous sows contribute to a better understanding of the ontogenetic development of pigs throughout their postnatal development.

Radioimmunoassay of progesterone in cow milk.

Fertilization checks in dairy cattle performed by estimation of progesterone in milk require a simple technique, the use of a sample taken independently of milking procedure and a simple management of the results. The laboratory equipped with a sample processor and pipetting device, high throughput counter for 125iodine and a tabletop computer can analyse about 1000 samples of fat-free milk in one day. The results are used for computer management of reproduction and veterinary service in farms with 600 to 2000 cows.

Characteristics of antibodies against 17 beta-oestradiol in homologous and heterologous systems of radioimmunoassay.

Directly iodinated oestradiol-2(4)-iodo-[125I] and oestradiol-6-O-(CMO)-[125I]iodohistamine were prepared and used in conjunction with anti-oestradiol-2(4)-azo and anti-oestradiol-6-O-(CMO) sera for the development of various radioimmunoassay (RIA) systems which showed marked differences in sensitivity and relatively small differences in specificity. Whereas the heterologous combination of oestradiol-6-O-(CMO)-[125I]iodohistamine and anti-oestradiol-2(4)-azo-serum showed a sensitivity expressed in femtograms, the homologous combination using oestradiol-6-O-(CMO)-[125I]iodohistamine radioligand exhibited a sensitivity two orders lower. The specificity of both the heterologous and homologous system did not differ significantly from the RIA system using tritiated radioligand. The combination of directly iodinated oestradiol and anti-oestradiol-2(4)-azo-serum showed a higher sensitivity and a lower specificity as compared with tritiated radioligand.

[The effect of a light regimen on the dynamics of biochemical indicators in the blood, serum and urine of heifers during 1 day]. / Vliv svetelného rezimu na dynamiku biochemických ukazatelu krve, séra a moce jalovic v prubehu jednoho dne.

Circadian dynamics of 38 biochemical parameters of the blood, serum and urine of heifers was studied under the natural light conditions of a light (160-180 lux) and dark (10-40 lux) small cow house. In each house, eight parameters were subject to a significant influence during the day, six of them being the same in both houses: calcium, chlorides, urea and thyroxine of blood serum, glucose and haematocrit in the blood of heifers. The comparison of parameters in different groups showed that different light regimes exerted a significant influence on calcium, chlorides, total protein, cholesterol, vitamin A and thyroxine in serum, haematocrit and leucocyte count in blood, and sodium and urea in the urine of heifers. The effect of feeding regime on the dynamics of parameters was tested by the calculation of the percentual fluctuation of their average values in heifer blood and serum before feeding (samples taken at 6.30 hrs) and after feeding (sampled at 10 hrs). In the light house, six parameters were judged to be less stable and one unstable (urea in serum). In the dark house six parameters were less stable and four unstable (calcium, urea, copper and thyroxine in serum).