Assessment of a parametric identification procedure of simple models for left ventricular afterload

Recently many studies have been devoted to the evaluation of the behaviour of the arterial system by calculating the left ventricular afterload, on the basis of the hydraulic impedance concept. Since the best known computation procedure, based on Fourier analysis, does not seem to be fully reliable, simple mathematical models have been set up by various investigators. One important problem is the choice of an identification procedure which points out the reliability of such models on the one hand, and which on the other hand allows us to compare them with each other. The behaviour of such a procedure can depend on operating conditions such as: (a) the choice of the input/output signals for the model (pressure or flow) and (b) the amount of noise and/or transient arterfacts added to these signals. Therefore, in the present work, the assessment of a parametric identification procedure has been studied relating to two different models previously proposed by the authors themselves, and its robustness has been evaluated in regard to the above mentioned conditions.     

Computing total arterial compliance of the arterial system from its input impedance

The total arterial compliance of the arterial system was computed from its input impedance by expressing the impedance in terms of its frequency-response vector diagram (f.r.v.) The f.r.v. plot of a 3-element windkessel subjected to random pacing follows, theoretically, a circular path. Since the windkessel model serves as a good approximation for the arterial system, we have used the simple properties of its f.r.v. plot to obtain the compliance, which is otherwise normally determined from the peripheral resistance and the time constant of the diastolic pressure decay. The arterial compliance can also be determined from the impulse response function of the arterial system. Data obtained from dog experiments during no intervention, aortic occlusion and during occlusion of both carotid arteries have been analysed.     

Influence of central and peripheral changes on the hydraulic input impedance of the systemic arterial tree

The input impedance of the systemic arterial tree of the dog has been computed by Fourier analysis. It was shown that a distance between pressure and flow transducers of less than 2 cm results in appreciable errors which manifest themselves mainly in the phase of the input impedance. The input impedance for controls, occlusions at various locations in the aorta, and an increase and decrease of peripheral resistance were studied. For the same experiments, the total arterial compliance was calculated from the peripheral resistance of the diastolic aortic-pressure curve. The characterstic impedance of the ascending aorta was also estimated. The impedance in the control situation may be modelled by means of a 3-element Windkessel consisting of a peripheral resistance and (total) arterial compliance, together with a resistance equal to the characteristic impedance of the aorta. The occlusions of the aorta show that blockage at (and beyond) the trifurcation do not result in a detectable change in input impedance, except for a slight increase of the peripheral resistance. The more proximal an aortic occlusion, the more effect it has on the pattern of the input impedance. When the aorta is occluded at the diphragm, or higher, the single (uniform) tube appears to be a much better model than the Windkessel. Occlusion of one or both carotid arteries increases the mean pressure; consequently not only the peripheral resistance increases but also the total arterial compliance decreases. The Windkessel with increased peripheral resitance and decreased compliance is again a good model. After a sudden release of occlusion of the aorta, the arterial system has a low peripheral resistance and may also be modelled by the Windkessel.     

Analytical relationship between arterial input impedance and the three-element Windkessel series resistance

The recently proposed energy-balance method for estimating the series resistance of the three-element Windkessel model is reformulated in the frequency domain. New mathematical expressions are analytically derived, involving Fourier harmonics of pulsatile arterial pressure and flow. It is shown that the series resistance of the arterial three-element Windkessel model can be expressed as a weighted sum of the arterial input impedance moduli.     

Quantitative dynamic contrast-enhanced MRI for mouse models using automatic detection of the arterial input function

Dynamic contrast-enhanced MRI (DCE-MRI) is widely accepted for the evaluation of cancer. DCE-MRI, a noninvasive measurement of microvessel permeability, blood volume and blood flow, is extremely useful for understanding disease mechanisms and monitoring therapeutic responses in preclinical research. For the accurate quantification of pharmacokinetic parameters using DCE-MRI, determination of the arterial input function (AIF) from a large arterial vessel near the tumor is required. However, a manual determination of AIF in mouse MR images is often difficult because of the small spatial dimensions or the location of the tumor. In this study, we propose an algorithm for the automatic detection of AIF from mouse DCE-MR images using Kendall's coefficient of concordance. The proposed method was tested with computer simulations and then applied to tumor-bearing mice (n = 8). Results from computer simulations showed that the proposed algorithm is capable of categorizing simulated AIF signals according to their noise levels. We found that the resulting pharmacokinetic parameters computed from our method were comparable with those from the manual determination of AIF, with acceptable differences in K(trans) (5.14 ± 3.60%), v(e) (6.02 ± 3.22%), v(p) (5.10 ± 7.05%) and k(ep) (5.38 ± 4.72%). The results of the current study suggest the usefulness of an automatically defined AIF using Kendall's coefficient of concordance for quantitative DCE-MRI in mouse models for cancer evaluation.     

An application of bioelectrical impedance for the detection of tissular bubbles in the diver: preliminary results

Symptoms that appear in the diver submitted to a fast decompression are known as decompression sickness. Rapid decompression causes bubbles of inert gases to form and grow within tissue or vascular space. Troubles only occur if bubbles are present in sufficient numbers. Ultrasonic Doppler techniques only permit the detection of great quantities of bubbles circulating in large vessels. A method using impedance measurement and the way to use it in hyperbaric fields are described. It allows the detection of tissular bubbles at an early stage by monitoring a muscular zone. The results obtained in the animal during traumatic decompressions and the initial results obtained in man during three experimental dives up to a simulated depth of 180 m of seawater shows a relationship between recorded impedance variations and the appearance of decompression sickness.     

Physiological and fluid-dynamic investigations of the transthoracic impedance plethysmography method for measuring cardiac output: Part I—A fluid-dynamic approach to the theory using an expansible tube model

The method of Nyboer and Kubicek for measuring stroke volume (s.v.) was used with an expansible tube model to analyse the relationship between the impedance variation and the actual flow. A preliminary correlation study between the method and electromagnetic flowmetry was conducted on 28 dogs: The correlation coefficient and the percentage of decentralisation within a ±25% error for the individual dogs were 0·79 and 53·5%, while those for a dog whose s.v. was controlled by drugs were 0·88 and 82·4%. The s.v. value and volume flow rate of a sinusoidal flow, as well as of a pulsatile flow, in the tube with an occluded outflow can be measured exactly by Nyboer's equation. In the tube with an opened outflow the s.v. value of the pulsatile flow can be measured only approximately by Kubicek's equation. In both tubes, the hydraulic frequency of the flow and the tube length are the most important factors governing the working frequency range of the method. Based on the results, we have discussed how to utilise the theory with a living subject.     

Comparison of two matrix-assisted laser desorption ionisation-time of flight mass spectrometry methods for the identification of clinically relevant anaerobic bacteria

Two commercially available MALDI-TOF MS systems, Bruker MS and Shimadzu MS, were compared for the identification of clinically relevant anaerobic bacteria. A selection of 79 clinical isolates, representing 19 different genera, were tested and compared with identification obtained by 16S rRNA gene sequencing. Correct genus identification was achieved for 71% of isolates by Shimadzu MS and for 61% by Bruker MS. Correct identification at the species level occurred in 61% and 51%, respectively. Shimadzu showed markedly better results for identification of Gram-positive anaerobic cocci. In contrast, the Bruker system performed better than Shimadzu for the Bacteroides fragilis group. When strains not present in the database were excluded from the analyses for each database, both systems performed equally well, with 76.7% and 75.0% correct genus identification for Shimadzu and Bruker, respectively. Similarly, when the most recently updated Bruker database was applied, no difference was observed. We conclude that the composition and quality of the database is crucial for a correct identification. The databases currently available for both systems need to be optimized before MS can be implemented for routine identification of anaerobic bacteria.     

Direction selectivity of simple cells in the primary visual cortex: comparison of two alternative mathematical models. II: Velocity tuning and response to moving bars

The two models of direction selectivity, presented in a previous paper, are used to investigate the response of simple cells to moving bars with different length, luminance and orientation. Most results agree with experimental data reported in the literature. However, a striking difference between the models is observable after a reduction in bar length. The antiphase model predicts that the optimal direction of movement for a short bar is equal to the optimal direction for a long bar, whereas the in-phase model predicts that the two optimal directions are orthogonal. This difference may allow experimental discrimination between the two models.     

A simple and rapid test for the identification of clinical herpes simplex virus isolates

A simple procedure is described which permits the rapid identification of clinical herpes simplex virus isolates. The test utilizes Staphylococcus aureus to which anti-viral immunoglobulins had been adsorbed. Adherence of the antibody-coated bacteria to virus-infected cells is readily seen by light microscopy. Indirect immuno-fluorescence and the S aureus adherence reaction were found to be approximately of equal sensitivity for the detection of virus antigens.     

In vivo determination of mechnical properties of the human ulna by means of mechanical impedance tests: Experimental results and improved mathematical model

An experimental technique and associated apparatus for measuringin vivo the mechanical impedance of the human ulna are described in detail. An electromagnetic shaker is used to apply a steady-state harmonic excitation to the ulna near its mid-span and measurements of the complex driving-point impedance are made. Both stiffness and resonant frequency information, useful in assessing the mechanical integrity of bone, are inferred from the impedance measurements by means of a third-generation mathematical model of the system. Results for three male and two female test subjects are reported.     

The bovine kidney as an experimental model: Simulated partial nephrectomy of the cranial pole and proportional analysis of the arterial segments

Previous studies have shown that the pig kidney is not a good model for some procedures. This study aimed to describe the relationship between the collecting system and the intrarenal arteries, the arterial segments, and to evaluate the bovine kidney as an experimental model for partial nephrectomy of the cranial pole. Polyester resin endocasts of the kidney collecting system together with the intrarenal arteries were prepared. Thirty-two kidneys were used to evaluate the relationship between the collecting system and the intrarenal arteries, while 25 kidneys were transversally sectioned at different points to simulate partial nephrectomy of the cranial pole. Polyester resin of different colors was injected into each segmental artery of the 24 kidneys to evaluate the arterial segments proportionally. The renal artery was divided into cranial and caudal primary branches in 75% of the cases. The cranioventral branch curved on the cranial pole and ran toward the ventral mid-zone in 56.3% of the cases, resembling the retropelvic artery of the human kidney. The kidney was divided into two (25%) or three (75%) arterial segments. The caudal arterial segment had the highest proportional volume (62%). The cranioventral branch was damaged in 28.6% of the kidneys sectioned 1 cm inside the hilum. The arterial branching pattern, the arterial segmentation, and the impairment of the arterial supply after the simulated partial nephrectomy of the cranial pole are quite different from those found in humans. Thus, all differences should be taken into account when using the bovine kidney as a model.     

Comparison bilaterally of lingual and facial arterial rami in the mandibulo-perimandibular complex: Arterioradiographic models for surgical consideration

Anatomic illustrations and arterioradiograms of the facial, submental, lingual and sublingual arteries, and their primary branches in the mandibulo-perimandibular complex are routinely demonstrated unilaterally; illustration and comparison bilaterally have not been documented. The unilateral illustration mode erroneously implies arterioanatomic similarity contralaterally. Mandibulo-perimandibular arteries in 50 stillborn human fetuses and 50 human adult cadavera were assessed. Head and neck arteries of fetal subjects were perfused with a radiopaque perfusant via the ascending thoracic aorta. Then the entire mandibular complex and tongue of each fetus was excised en bloc and radiographed from above the tongue. The radiograms showed 1) that sublingual and submental arteries and their primary rami differ in size, number, arrangement, and distribution unilaterally, as well as bilaterally and 2) that the entire mandibular body complex (including periosteum, cortex, spongiosa, and dentoparadontal structures) receives substantial sources of supply via the facial, submental, and sublingual arteries (extrinsic sources). The facial and lingual arteries and their ramifications in the adult mandibular complex were demonstrated by gross dissection. Comparison between fetal and adult mandibular arterial anatomies showed remarkable similarity. Furthermore, the results of this arterio-anatomic assessment and the results of concurrent, independent, experimental bone surgical studies (Hadidi, Doctoral dissertation, Medical College of Wisconsin, Milwaukee 1985) favor a growing opinion that rami from the facial, submental, and sublingual arteries (extrinsic sources) to the mandibular body are more essential to its need than is commonly believed. © 1993 Wiley-Liss, Inc.     

Development of RNA-SSCP protocols for the identification and screening of CFTR mutations: Identification of two new mutations

A strategy is described that allows a rapid and accurate identification and screening of cystic fibrosis gene mutations. It consists of setting up and developing RNA single strand conformation polymorphism (rSSCP) protocols, a technique based on the large repertoire of secondary structure of single-stranded RNA. By incorporating the T7 phage promoter sequence into PCR primers, it is possible to carry out rSSCP and compare it to standard single-strand conformation polymorphism (SSCP). Several parallel tests indicate that rSSCP detects a higher fraction of single base changes, and is less time consuming than SSCP since it requires only one fairly short electrophoretic run. Using this technique we were able to identify two new splicing mutations in introns 5 (711+5G→A) and 10 (1717–8G→A) of the CFTR gene. © 1994 Wiley-Liss, Inc.     

乌鲁木齐地区679例病残儿医学鉴定结果分析

目的对乌鲁木齐市679例病残儿进行分析,找出相关因素,为减少出生缺陷,降低病残儿的发生,提高人口素质,提供科学依据。方法对1998年~2012年鉴定审批合格、同意再生育的679例病残儿档案逐一清查核实,并进行整体分析。结果病残儿年龄1~14岁,男孩多于女孩,检出疾病共41种,其中遗传性疾病、非遗传性疾病各占45.85%、54.15%。679例病残儿母亲年龄以3O~35岁最多。结论开展优生优育遗传咨询,加强出生缺陷干预,可预防和减少病残儿的发生。     

Mechanistic QSAR of aromatic amines: new models for discriminating between homocyclic mutagens and nonmutagens, and validation of models for carcinogens

Because of its environmental and industrial importance, the aromatic amines are the single chemical class most studied for its ability to induce mutations and cancer. The large database of mutagenicity and carcinogenicity results has been studied with Quantitative Structure-Activity Relationship (QSAR) approaches by several authors, leading to models for the following: (a) the mutagenic potency in Salmonella thyphimurium; (b) the carcinogenic potency in rodents; and (c) the discrimination between rodent carcinogens and noncarcinogens. However, satisfactory models for the discrimination between mutagens and nonmutagens are lacking. The present work provides new QSARs for mutagenic/nonmutagenic homocyclic aromatic amines in S. typhimurium strains TA98 and TA100. The two new models are validated by checking their ability to predict the mutagenicity of further aromatic amines not included in the training set, and not used to generate the QSAR models. In addition, we also validated previous QSAR models for the carcinogenicity/noncarcinogenicity of the aromatic amines with external data. The mechanistic implications of the models are discussed in light of the other QSARs for the aromatic amines. The results of the analysis point to two QSAR models (one for mutagenicity and one for rodent carcinogenicity) as reliable tools for the in silico characterization of the risk posed by the aromatic amines.     

Prototype of dual energy x-ray tomodensimeter for lumbar spine bone mineral density measurement: choice of the reconstruction algorithm and first experimental results.

A dual-energy x-ray tomodensimeter adapted for the determination of bone mineral density (BMD) of the lumbar vertebrae has been directly developed from a typical dual-energy x-ray absorptiometer. This apparatus consists of two fundamental parts: a dual energy x-ray tube, and a multidetector made by an array of 24 NaI(T1) crystals. It provides both tomographic and non-tomographic (anteroposterior, lateral etc) measurement. The detection area is limited to 132 mm. In this condition, the choice of the best reconstruction algorithm in order to give a direct BDM is considered. Preliminary studies based on numerical simulated projections and hydroxyapatite phantoms demonstrated the superiority of algebraic reconstruction algorithms, such as conjugated gradient, in order to resolve the problems of (i) the impossibility of defining an internal calibration, and (ii) the potential for reconstruction errors due to the presence of bone structures located out of the detection area. The accuracy of BMD measurement is within 2%, with in vitro precision approximately 1%, and linearity characterized by a standard error of estimation (SEE) of 2 mg cm-3 in the range of lumbar BMD (less than 400 mg cm-3). Experimental data derived from two volunteers are presented.     

A simplified new method for the identification of arboviruses: virus detection using enzyme immunoassay on cultured cells

A simple new method is reported for the identification of arbovirus isolates and the titration of arboviruses. Horseradish peroxidase conjugated Staphylococcus aureus protein A was used for the indirect staining of virus antigens grown in an Aedes albopictus cell line, C6/36 cells. Thirty-five isolates from Culex tritaeniorhynchus mosquitoes were examined by this method and 20 of these were identified as Japanese encephalitis virus (JEV). These results were confirmed by immunofluorescent assay and plaque neutralization test. Comparative titration of JEV, Murray Valley encephalitis (MVE) and Kunjin viruses showed that this method was as sensitive as the chick embryo plaque assay. Specific enzymatic reactions on these virus-infected cells began to appear before day 3 and reached the end-point on day 5 post-infection of C6/36 cells, whereas the cytopathic effect (CPE) appeared about 2 days later than the positive enzymatic reactions. Fixation with 10% formalin for 0.5-8 h did not damage the positive reaction in infected cells and did not increase the background colour of uninfected cells.