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Biomedical subjects

P Barbini

Publications and source records attributed to P Barbini.

At least 55 records · Page 3Linked to original sources
PubMed1989

Sensitivity analysis of the systemic circulation with a view to computer simulation and parameter estimation.

A sensitivity analysis study has been performed on a seven-parameter model of the systemic vascular bed in order to obtain structure reductions appropriate for simulation and estimation. This analysis considers separately the systolic and diastolic transfer functions between arterial and venous pressures in order to divide a non-linear problem in two distinct linear problems. The results obtained refer to nominal parameter values corresponding to normal circulatory conditions in man and supply guide-lines for an application-oriented selection of reduced models. Simple resistance-compliance models are preferred because the inertial effects appear to have only slight influence. In particular, the choice of a five-parameter model seems to be convenient for simulation purposes. An additional structure reduction is suggested to reach reliable results in parameter estimation problems. The resulting model is characterized by three elements: peripheral resistance, arterial compliance and venous compliance.

Blood Circulation↗
PubMed1989

The nuclei in cutaneous malignant melanoma, stage I, are smaller in survivors than in non-survivors.

Cutaneous melanoma, stage I, from 35 survivors at 5 year follow-up and 16 non-survivors were studied. Mean nuclear area in the superficial layer was significantly larger than in the deep layer both in survivors and non-survivors, but the ratio between nuclear area in superficial and deep layers (so-called maturation index) did not differ between survivors and non-survivors. In comparison with the survivors, the mean nuclear area of non-survivors was significantly larger both in the superficial (51.1 microns2 vs 43.7 microns2, p less than 0.01) and deep (42.9 microns2 vs 36.4 microns2, p less than 0.05) layer. This points to a general increase in nuclear areas in metastasizing tumors. Furthermore, the coefficient of variation of nuclear area [(standard deviation/mean) x 100] was not different between survivors and non-survivors, either in the superficial or in the deep layer. Inspection of histograms of areas of 1000-2000 nuclei per case in 20 random cases (10 survivors and 10 non-survivors) showed a homogeneous increase in nuclear area in non-survivors. None of the histograms revealed a cell clone with especially large nuclei. These data show that the increased mean nuclear area in non-survivors is due to a homogeneous increase of all nuclei throughout the tumor and not to a special cell clone with large nuclei within nuclei of otherwise normal size. The difference in mean nuclear area in superficial and deep layers indicates that careful selection of nuclei in either of these layers is essential to obtain reproducible and comparable results with interactive morphometry.

Cell Nucleus↗
PubMed1989

Electrical analogs for monitoring vascular properties in artificial heart studies.

The problem of choosing parametric descriptions of the systemic vascular bed suitable for monitoring beat-to-beat changes in peripheral vascular properties is considered. Three simple models with two, three, and five elements are compared, essentially exploiting the Akaike information criterion combined with reasonable requirements for estimate accuracy. Analysis of pressure data, which are either simulated by the five-element model or measured on a mock circulatory system during abrupt changes in peripheral resistance, suggests guidelines for model selection. In particular, the five-element model exhibits very close adherence to physical reality by allowing for reflection, while the classical windkessel model provides the most reproducible estimates.

Cardiovascular Physiological Phenomena↗
PubMed1989

Tracking time-varying properties of the systemic vascular bed.

The problem of tracking changes in viscoelastic properties of the systemic arterial bed is considered and a recursive estimation procedure, belonging to the class of output-error algorithms with adjustable compensator, is developed and discussed. By means of computer simulations, suitable values are determined for the key design variable which controls the tradeoff between tracking ability and noise sensitivity of the algorithm. In this way, the algorithm allows on-line estimation of arterial compliance, peripheral resistance, and characteristic impedance on the basis of aortic pressure and flow signals. Furthermore, the results obtained from data numerically simulated, as well as measured on a mock circulatory system, demonstrate that the dominant arterial time-constant can be tracked by the algorithm using only measurements of the aortic pressure during diastole.

Algorithms↗
PubMed1989

Histopathological evaluation for the prognosis of retinoblastoma.

In the present study histologic, clinical and follow-up data of 37 cases of retinoblastoma were statistically analyzed by means of a multivariate method. The evaluated histological parameters were: growth pattern, degree of differentiation, number of mitoses, presence of necrosis, pseudorosettes, blood vessel basophilia, calcification, extension to anterior chamber, invasion of optic nerve and ocular coats (choroid and sclera). The analysis was based upon the Cox proportional hazards regression model. Invasion of ocular coats proved to be highly correlated to the prognosis (p less than 0.0002). None of the other parameters showed a significant relation to survival.

Child↗
PubMed1988

CADCS simulation of the closed-loop cardiovascular system.

A pulsatile simulator of the closed-loop cardiovascular system, designed to solve simulation, identification and control problems in a research and education context, is presented. Its implementation makes use of a command-driven interactive program for simulation of non-linear ordinary differential equations. The flexibility of the simulator is demonstrated by the results presented which refer to a basal steady-state circulatory condition as well as a transient induced by an abrupt change in peripheral resistance.

Blood Pressure↗
PubMed1988

Mantle zone lymphoma: a morphometric comparison with centrocytic and immunocytic lymphomas and reactive secondary follicles.

Nuclear size and shape of lymphoid cells were evaluated morphometrically in the mantle zone lymphoma, immunocytic lymphoma, and centrocytic lymphoma, and were compared with those of reactive secondary follicles. Shape factors (forms Ar, Ell, Pe, and Dia) have been used to quantitatively define the most frequent nuclear profiles. One of the testing sets consisted of the nuclei of the light, dark, and mantle regions of reactive nodes, as well as those of the centrocytic lymphoma, immunocytic lymphoma, and the mantle-fashion growth lymphoma. Another testing set was made up of only the three types of lymphoma and was used for evaluating the variability of shapes within these groups by means of a pattern recognition algorithm. The content of reactive T lymphocytes was assessed in all cases by immunohistochemistry. The results of transforming centroid values into geometric shapes by computer modelling indicated that only minor geometric differences existed between the a priori qualitatively chosen nuclear types and those modeled a posteriori by computer. All the nuclear types were found in each of the reactive regions and in each of the lymphomas. However, highly significant differences of distribution were detected among the three categories of lymphoma and between each reactive region and each lymphoma. The cases of centrocytic lymphoma showed constant findings in terms of nuclear composition, while lymphomas with mantle-fashion growth and the examples of immunocytic lymphoma showed significant variability. These observations confirm that the centrocytic lymphoma represents a distinct entity, although its normal counterpart is still unknown, and question the view that the immunocytoma and the mantle zone lymphoma correspond to homogenous categories of non-Hodgkin's lymphomas. In addition, since all the qualitatively and quantitatively detected nuclear types were found in all the reactive regions and in all the lymphomas, albeit with different distributions, it has to be assumed that only numerical differences exist among the various lymphomas and the reactive regions.

Adult↗
PubMed1988

Comparative morphometric analysis of nuclear area and shape in peripheral T-zone lymphomas and in paracortical areas of normal and reactive lymph nodes.

The areas and shapes of cell nuclei were morphometrically analyzed in peripheral T-zone lymphomas, which have a characteristic nuclear pleomorphism, as well as in paracortical areas of normal and reactive lymph nodes; the aim of the study was to compare the neoplastic and nonneoplastic lymphoid cell populations. Although the means and standard deviations (SDs) of nuclear area and shape features differed significantly between the T-zone lymphomas, reactive nodes and normal nodes, there was considerable overlap between the lymphomas and the reactive lymph nodes in all of the features investigated. Therefore, the composition of populations of nuclei was studied. In lymphomas, the frequencies of regular and irregular nuclei were about the same in all nuclear area classes, whereas increasingly larger nuclei had an increasingly regular shape in reactive lymph nodes. An attempt to classify the cells, divided into those with small nuclei (less than 25 sq microns) and those with large nuclei (greater than 25 sq microns), on the basis of their morphometric shape features showed the usefulness of form factors in the class of nuclei with a large area. The results show that, while means and SDs of nuclear area and shape are not very accurate descriptors of the differences between the T-zone lymphomas and nonneoplastic lymph nodes, analysis of the percentage of regularly shaped nuclei in a certain nuclear area class can describe the differences much more accurately. The compositional differences in nuclear shape are in agreement with subjective impressions and can objectively support the pathologist's qualitative impression of pleomorphism in malignant T-zone lymphomas.

Adult↗
PubMed1987

Gastric dysplasia: a stereological and morphometrical assessment.

The grading systems of gastric dysplasia suffer from the lack of criteria that separate the changes with an acceptable reproducibility. Repeatable and objective grading of the lesion can be obtained by morphometrically measuring histological criteria normally employed in qualitative grading. In 54 consecutive antrum biopsy specimens in which a blind, independent agreement on the grade of dysplasia had been reached between four independent pathologists, stereological and nuclear morphometrical features have been studied. Single variate, bivariate and multivariate analyses have been performed. Architectural parameters, such as volume and surface densities of glands and epithelium, are especially good discriminators both between mild and moderate, and between moderate and severe dysplasia. Features describing arrangement and shape of nuclei, and nucleolar size are of additional help in improving the objective distinction between moderate and severe dysplasia.

Adult↗
PubMed1987

Three-element model for total systemic circulation: emphasis on the accuracy of parameter estimates.

In this study, the accuracy achievable in the parameter estimates of a three-element linear model for the systemic vascular bed is considered. The model neglects inertial effects and includes only three elements representing arterial compliance, peripheral resistance and venous compliance, in agreement with recent sensitivity investigations. Parameter estimation starts from arterial and right atrial pressure signals generated by a closed-loop simulator of the cardiovascular circulation and corrupted with normal noise to account for measurement errors. In this way, the influences of a wide variety of circulatory conditions were investigated. The results achieved give evidence that arterial compliance is generally well estimated, while venous compliance is more variable, particularly at high peripheral resistance when measured signals appear to be less sensitive to this parameter. However, presence of cardiac disease, such as heart failure and valvular stenosis has minimal influence on compliance estimates. These results suggest that this simple model can be conveniently applied even under noisy conditions.

Blood Circulation↗
PubMed1986

Correlation between morphometrical parameters and disease-free survival in ductal breast cancer treated only by surgery.

A combination of quantitatively evaluated morphological parameters and of conventional prognostic indicators has been used to study 19 cases of invasive ductal breast carcinoma from patients treated only by surgery, later developing recurrences or metastases. This set of patients not treated with adjuvant therapy (radiotherapy, cytostatic or hormonal therapy), was selected from 350 consecutive breast cancers which had been treated with surgical therapy. The aim was to investigate whether the morphometrical features are correlated with disease-free survival. Of the single features, the mitotic activity index (MAI) is most strongly correlated with prognosis. Ten of the 19 patients had an MAI value above 9, and all of them recurred within 18 months. In contrast, of the 9 other patients with low mitotic rate (MAI below or equal to 9), none recurred within 24 months. Further, a correlation exists between disease-free survival, mean and standard deviation of nuclear and nucleolar area, and tubular component of the tumors. There is no correlation between nuclear form factors and recurrence. The multivariate prognostic score is also significantly correlated with recurrence, but not as strongly as in other publications. This is obviously due to the blurring influence of the lymph node status, which was not significantly correlated with the prognosis. Thus, in this small set of patients not treated with any adjuvant therapy, the results of morphometric analysis are in agreement with earlier data and emphasize the prognostic significance of quantitative microscopical analysis in breast cancer.

Adult↗
PubMed1984

Sensitivity analysis for an improved estimation of respiratory mechanics parameters.

In this paper a respiratory mechanics model is considered, which is characterized by a biquadratic input impedance, and a sensitivity analysis has been carried out to determine the influence of experimental conditions on parameter estimation. This analysis was effected with data obtained experimentally, in three different patients under intermittent positive pressure ventilation. In all three cases, the model's input impedance demonstrated a maximum sensitivity in relation to the various parameters included in the field of frequencies from 0 to 10 Hz. This seems to suggest therefore, that the use of a low-pass filter with a cut-off frequency equal to 10 Hz could improve the signal/noise ratio and, consequently, the accuracy of the estimation of the parameters. Furthermore, the use of a system input with a bandwidth of 0-10 Hz provides the experimental conditions, under which good estimates of the parameters can be obtained. This conclusion has also been confirmed by simulation studies which have been conducted with different types of input signals.

Biomechanical Phenomena↗
PubMed1982

Non-linear model of the mechanics of breathing applied to the use and design of ventilators.

Respiratory treatment involves clinical problems which are often related to the pulmonary and circulatory condition of the patient. Choice of a proper respirator and its adequate use are very important for overcoming a good deal of the clinical problems which may arise. A good automatic ventilator should, under all circumstances, be capable of assuring a suitable gas exchange at the pulmonary level with as little alteration as possible to the physiological functions of the body. In this paper a non-linear model of the mechanics of breathing is used to examine: (1) the effects of four theoretical inspiratory flow patterns in intermittent positive pressure ventilation (IPPV); (2) the differences obtained with respect to IPPV when we use a positive end-expiratory pressure (PEEP) or a negative pressure in the expiratory phase (IPNPV); (3) the performances of four automatic ventilators at present on the market and commonly used in departments of anaesthesia and intensive care. The results obtained by simulation of the respiratory system indicate that, in practice, an ideal ventilator neither exists nor can be designed. The manner of using the ventilator leads to different results, more so than the theoretical inspiratory flow pattern or the type of ventilator used. The tables and graphs shown in the paper help to utilize the ventilator in such a way as to optimize the parameters which, each time, are considered the most important.

Biomechanical Phenomena↗