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Biomedical subjects

G Cevenini

Publications and source records attributed to G Cevenini.

At least 37 records · Page 2Linked to original sources
PubMed1998

Instrumental measurement of skin colour and skin type as risk factors for melanoma: a statistical classification procedure.

A statistical procedure to evaluate melanoma risk in Caucasian subjects on the basis of colorimetric measurement of skin colour and Fitzpatrick phototype is described. One hundred and sixty melanoma patients and 546 randomized healthy subjects of similar age, sex and place of origin were examined in the same period for skin colour using a tristimulus colorimeter and for Fitzpatrick phototype. A clinical score for classification purposes was obtained by statistical discriminant analysis with multivariate data transformation and dimension reduction techniques. A Fisher linear classifier was chosen for its simplicity and robustness in correctly predicting melanoma risk in new subjects. The classification rule was designed to avoid classifying subjects at high risk for melanoma as low risk, i.e. to give a negligible number of false negatives at the expense of more false positives. The procedure is objective and readily adapted to different clinical requirements. This is only a preliminary study but it is hoped that by performing more complex statistical analyses, e.g. neural networks, and adding other parameters (proven risk factors such as number of naevi) the performance will be further improved.

Colorimetry↗
PubMed1998

Relationship between minimal phototoxic dose and skin colour plus sun exposure history: a neural network approach.

Before beginning PUVA-therapy it is important to accurately gauge an individual's degree of psoralen photosensitivity. This determination is usually based on an individual's skin phototype or minimal phototoxic dose. Since minimal phototoxic dose is technically complex and time consuming to measure, sun reactivity skin phototype is often used instead; however, it has recently been shown that skin phototype lacks specificity as a predictor of an individual's minimal phototoxic dose. In this study, an artificial neural network was developed to attempt to predict the minimal phototoxic dose from skin colour measurements combined with skin phototype. Our results showed that minimal phototoxic dose was predicted with an error less than 1 J/cm2 in only about half the subjects. In conclusion, minimal phototoxic dose probably cannot be predicted with sufficient accuracy on the basis of skin colour and skin phototype alone.

Adult↗
PubMed1998

Combined use of single and double-cross steel wires for closure of midline sternotomy.

BACKGROUND: We describe an improved technique for sternal closure which is performed using combined single and double-cross steel wires. We made a mechanical study of these single and double-cross shapes considering the effects of applied transverse and longitudinal shearing forces. METHODS: We used this technique in 80 patients who underwent coronary surgery with the use of bilateral internal mammary arteries. RESULTS: Among them no major wound complications occurred, and in all cases a firm stabilization of the sternum was achieved. CONCLUSIONS: We therefore consider this technique of sternal closure easy, safe and effective, also in patients considered at risk for sternal dehiscence.

Bone Wires↗
PubMed1997

Relationship between skin color and sun exposure history: a statistical classification approach.

In this study our aim was to determine the biophysical values of constitutive skin color in Caucasians and to define the correlation between skin color and phototype assessed according to the Fitzpatrick method. Constitutive skin color was measured on the buttock, with a Minolta CR-200 colorimeter, in a population-of 557 consecutive subjects belonging to phototype categories I, II, III and IV. The colorimeter expresses the results in five different color systems. We used the "Yxy" and L*a*b* systems, which are the most widespread in dermatology. Statistical analysis of the data showed that the "Yxy" system is even more discriminant than the L*a*b* system when the Fitzpatrick classification scheme is adopted as the reference and shows a poor ability to correctly classify the intermediate phototypes (II and III). On the contrary the "Yxy" system performs well in distinguishing phototypes I and IV. To establish whether this low discriminating capacity for phototypes II and III is related to a low discriminating capacity of the method suggested by Fitzpatrick or by our procedure, an objective technique (minimal erythemal dose) should be used to evaluate the percentage errors of classification of both the Fitzpatrick method and instrumental measurement of skin color. The results of such a study are extremely important because the evaluation of skin color is objective, simple and has potential applications in dermatology and cosmetology.

Adult↗
PubMed1996

Nearest-neighbor analysis of spatial point patterns: application to biomedical image interpretation.

Analysis of the spatial distributions of objects is fundamental to biomedical image interpretation. Nearest-neighbor (NN) methods are generally used to assess whether objects are arranged at random or in a deterministic manner. Simple standard NN techniques, however, may fail to identify complex spatial organizations. To overcome this problem the present study proposes a NN iterative algorithm that enables deterministic spatial patterns to be detected by identifying the distances between objects for which there is the greatest deviation from randomness and hence the amplitude of the areas of maximum reciprocal influence between objects. The performance of the algorithm is evaluated by applying it to both manufactured and experimental data. The manufactured date example showed that the proposed procedure produced neither false positives or negatives. The method proved to be extremely sensitive, detecting even small deviations from randomness. The experimental analysis was applied to the study of the spatial distribution of apopototic structures in malignant neoplastic tissue. It showed that the apopototic cells and bodies are characterized by a complex spatial pattern, and aggregate closely.

Algorithms↗
PubMed1995

Two new algorithms for tracking arterial parameters in nonstationary noise conditions.

Two new algorithms with reduced sensitivity to the changing environment are applied to tracking arterial circulation parameters. They are variants of the Least-Squares (LS) algorithm with Variable Forgetting factor (LSVF), and of the Constant Forgetting factor-Covariance Modification (CFCM) LS algorithm, devised to overcome their main practical deficiencies related to noise level sensitivity and the high number of design variables, respectively. To this end, adaptive mechanisms are incorporated to estimate observation noise variance in LSVF and the rate of change for the different parameters in CFCM. Specific computer simulation experiments are presented to compare their effectiveness with the original counterparts and to provide guidelines for their optimal tuning at different noise levels. Moreover, algorithm performance degradation, consequent on changes in the noise level compared to that assumed during the tuning phase, is analyzed. In particular, it is shown that, when the noise level changes with respect to the tuning value, the new LSVF algorithm is much more robust than the original one, whose performance degrades rapidly. The new CFCM algorithm is characterized by a reduced number of design variables with respect to its original counterpart. Nevertheless, it can be preferred only when low noise signals are used for estimation.

Algorithms↗
PubMed1995

Influence of flow pattern on the parameter estimates of a simple breathing mechanics model.

The first-order model of breathing mechanics is widely used in clinical practice to assess the viscoelastic properties of the respiratory system. Although simple, this model takes the predominant features of the pressure-flow relationship into account but gives highly systematic residuals between measured and model-predicted variables. To achieve a better fit of the entire data set, an approach hypothesizing deterministic time-variations of model parameters, summarized by information-weighted histograms was recently proposed by Bates and Lauzon. The present study uses flow and pressure data measured in intensive care patients to evaluate the real potential of this approach in clinical practice. Information-weighted histograms of the model parameters, estimated by an on-line identification algorithm, were first constructed by taking into account the parameter percentage standard deviations. Then, the influence of the respiratory flow pattern on the calculated histograms was evaluated by the Kolmogorov-Smirnov statistical test. The results show that the method gives good reproducibility under stable experimental conditions. In addition, for a given airflow waveform, an increase in respiratory frequency shifts the histograms representing time-varying viscous properties strongly versus lower values, whereas it shifts the histograms representing time-varying elastic properties slightly versus higher values. On the other hand, the same histograms were highly dependent on the airflow waveform, especially for the viscous properties. Even in a limited experimental work, in all the conditions considered, the method provides results which agree well with the physiological knowledge of nonlinear and multicompartment behavior of respiratory mechanics.

Algorithms↗
PubMed1994

Ploidy pattern and cell cycle in breast cancer as detected by image analysis and flow cytometry.

Both image analysis (IA) and flow cytometry (FCM) may be applied to detect ploidy pattern and cell cycle fractions. However, they have different performance characteristics and may yield different results. The two approaches are applied in this study to 66 breast cancers: IA on imprints and FCM on fresh tissue. The percent coefficient of variation (CV) ranged from 2.0 to 7.0 (mean 5.5; SD 1.1) in IA and from 2.0 to 7.0 (mean 4.4; SD 1.1) in FCM. The values were well correlated. With regard to ploidy pattern, the agreement between the two methods was 92.4%; disagreements were due to four cases being aneuploid by IA but not detected by FCM and one case being aneuploid by IA but tetraploid by FCM. This suggests that IA is capable of detecting aneuploidy with more sensitivity than FCM. In diploid cases, the percent values of cells in G0/G1, S-phase (SPF), and G2M phase were concordant and well correlated. In aneuploid cases, IA was more sensitive than FCM in detecting aneuploid fraction as well as G2M phase, whereas FCM was more sensitive than IA in detecting SPF. A good correlation was found between the DNA indexes (DIs) obtained with the two methods.

Aneuploidy↗
PubMed1994

Estimating respiratory mechanical parameters of ventilated patients: a critical study in the routine intensive-care unit.

Airflow and pressure were measured post-operatively in eight mechanically ventilated patients in the routine intensive care unit. Analysis of the input impedance spectra versus frequency suggested that respiratory data cannot be adequately reproduced using the classic two-element R-C model, as the real part of input impedance decreases with frequency. To fit in with this behaviour, we adopted a three-element model with an additional parallel compliance. The three parameters of this model were estimated separately in the frequency and time domains by minimising suitable least-square criterion functions. The results demonstrate a good agreement between the parameter estimates in the frequency and time domains, and show that the three-element model reproduces the input impedance frequency pattern in the range 0.2-8 Hz. Comparison of different linear models in the time domain demonstrated that the precision of parameter estimates and the quality of best fitting sharply increase from the two-element to the three-element model. The addition of a fourth resistive parameter, like in the Mead model, does not lead to appreciable improvement and makes the model almost unidentifiable. The possible contribution of a ventilator-patient circuit of the upper airway shunting and of the peripheral airway obstruction are also discussed.

Airway Resistance↗
PubMed1993

Low-frequency respiratory mechanics using ventilator-driven forced oscillations.

We evaluated the potential for using a fast Fourier transform (FFT) analysis applied to a standard ventilator waveform to estimate (< 2 Hz) frequency dependence of respiratory or lung resistance (R) and elastance (E). In four healthy humans we measured pressure and flow at the airway opening while applying sine wave forcing from 0.2 to 0.6 Hz at two tidal volumes (VT; 250 and 500 ml). We then applied a step inspiratory ventilator flow wave with relaxed expiration at the same VT and only 0.2 Hz. Step waveform data were also acquired from nine mechanically ventilated patients under intensive care unit conditions. Finally, we simultaneously measured total respiratory (rs), lung (L), and chest wall (cw) impedance data from two dogs (0.156-2 Hz) before and after severe pulmonary edema. Rrs and Ers were estimated by the FFT approach. Humans displayed a small frequency dependence in Rrs and Ers from 0.2 to 0.6 Hz, and both Rrs and Ers decreased at the higher VT. The spectral estimates of Rrs and Ers with the step ventilator wave were often qualitatively comparable to sine wave results below 0.6 Hz but became extremely erratic above the third harmonic. Conversely, in dogs the step wave produced reliable and stable estimates up to 2 Hz in all conditions. Nevertheless, Ecw and Ers still displayed clear and correlated oscillations with increasing frequency, whereas EL showed none. This suggests that nonlinear processes, most likely at the chest wall, contribute to periodic-like fluctuations in respiratory mechanical properties when estimated by applying FFT to a step ventilator wave. Moreover, in humans, but not dogs, a ventilator flow cycle contains insufficient signal energy beyond the third harmonic. We show that the amount of energy available at higher frequencies is largely governed by the mechanical time constant contributing to passive expiratory flow. In dogs the shorter time constant contributes to increased energy. In essence, the frequency content of the flow is subject dependent, and this is not a desirable situation for controlling the quality of the impedance spectra available from a standard ventilator wave.

Adult↗
PubMed1992

Bronchiolo-alveolar carcinoma: an analysis of survival predictors.

Macroscopic and microscopic features of tumours have been analysed in 37 bronchiolo-alveolar carcinomas. Lymphocytes, Langerhans cells, collagen (mature and/or myofibroblastic), were quantitatively or semiquantitatively evaluated. Histology, stage, type of fibrosis, nuclear profile features (area and shape factors), amount and type of mucin secreted, number of mitoses, Langerhans cells, myofibroblasts and LeuM1+ cells were not related to survival. Gross morphology of the tumour and, to a lesser extent, lymphoid infiltrates (in particular UCHL1+ and L26+ peritumoral lymphoid cells) were the only variables significantly related to survival. Estimated survival functions were computed according to Cox's model: well demarcated tumours behaved significantly better than poorly demarcated tumours and even more so than diffuse or multiple mass. Lymphoid infiltrates were significantly more represented in and around well demarcated tumours: however, their survival predicting value was less than that of the gross type.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1991

Classification of postoperative cardiac patients: comparative evaluation of four algorithms.

Four classification algorithms based on Bayes' rule for minimum error are compared by evaluating their ability to recognize high- and normal-risk cardio-surgical patients. These algorithms differ in the modelling of the probability density function (pdf) for each class and include: (a) two parametric algorithms based on the assumption of normal pdf; (b) two non-parametric algorithms using Parzen multidimensional approximation of pdf with normal kernels. In each case, classes with both equal and different covariance matrices were considered. A set of 200 patients in the 6 h immediately following cardiac surgery has been used to test the performance of the algorithms. For each patient the three measured variables most effective in representing the difference between the two classes were considered. We found that the two algorithms which explicitly incorporate the information on the different sample covariance between the physiological variables existing in the two classes generally provide better recognition of high- and normal-risk patients. Of these two algorithms the parametric one appears extremely attractive for practical applications, since it exhibits slightly better performance in spite of its great simplicity.

Algorithms↗
PubMed1990

Real-time tracking of parameters of lung mechanics: emphasis on algorithm tuning.

We consider the problem of tracking rapid changes in the viscous and elastic properties of the respiratory system by using mouth flow and transpulmonary pressure data measured during mechanical ventilation. A recursive least-squares algorithm with adjustable compensator is used for online estimation of an R-C model of the breathing mechanics. Specific simulation experiments are presented to provide guidelines to select suitable values for the key variable, which controls the compromise between tracking ability and noise sensitivity. The results obtained confirm the critical role of the optimum tuning in relation to the noise level. Experimental results obtained from data measured on mechanically-ventilated dogs, in which respiratory distress syndrome was intravenously induced by oleic acid, demonstrate that the tuned algorithm is able to track appropriately both the viscous and elastic properties of lung mechanics. Parameter estimates are consistent with those obtained by standard and robust offline algorithms and their time course is in qualitative agreement with known physiopathological behaviour.

Airway Resistance↗
PubMed1990

Hodgkin's disease and CD30-positive anaplastic large cell lymphomas--a continuous spectrum of malignant disorders. A quantitative morphometric and immunohistologic study.

The authors have examined cellular areas of lymphoma tissue in 28 cases of Hodgkin's disease (HD) or anaplastic large cell lymphoma (ALCL, 'Ki-1 cell lymphoma') to evaluate the boundaries between the two entities. Methods applied included conventional histology; test point analysis; semiautomated morphometry of nuclear profile features of Reed-Sternberg and other atypical large cells (RSALCs); and immunohistochemistry of these elements on all paraffin sections and, in 15 cases, on frozen sections. Mean nuclear profile morphotypes of RSALCs per case varied independently of immunophenotype and histologic diagnosis. Conversely, immunohistochemistry demonstrated significant, although not consistent, preferential positivities of these CD30+ elements for CD15 in HD, and for epithelial membrane antigen (EMA) and CD43 in ALCLs. In the latter, RSALCs also exhibited a tendency for CD45 and CD45RO positivity and for the expression of T-cell-associated antigens. However, there were considerable overlaps. This continuous spectrum of RSALC nuclear profile morphotypes and immunophenotypes, ranging from HD over questionable cases, intermediate between HD and ALCL, to ALCLs, was paralleled by differences in the reactive component of lymphomas. Lymphocytes and granulocytes were significantly deficient in ALCLs.

Adolescent↗
PubMed1990

Heterogeneous subgroups among malignant diffuse small B cell lymphomas. A combined nucleometric and immunocytologic study.

The degree of heterogeneity among subtypes was evaluated in 39 of the most frequent malignant, diffusely growing small B cell lymphomas by a combination of morphometry, automated image analysis, and immunocytologic techniques. Cluster analysis of nuclear profile parameters, including nuclear area, circularity factor, and chromatin distribution pattern, distinguished 3 groups. Each group was characterized by the preponderance of certain nuclear profile types, i.e. (a) small, rather regular (roundish) and dark staining (typical small lymphocytic lymphomas and immunocytomas); (b) small to intermediate size, rather regular (roundish) and pale staining (small to intermediate size variant); or (c) small to intermediate size, irregular, rather pale staining (diffuse follicular small cleaved cell (centrocytic) lymphomas and, probably, polymorphous immunocytomas). Group 3 was clearly distinct from the rest, but groups 1 and 2 also differed significantly. Every case displayed a mixture of the 13 registered nuclear profile types. Lymphoid cells with similar nuclear profile features occurred in B cell zones of non-neoplastic lymph nodes. Frequency distribution of nuclear profile parameters significantly differed from one lymphoma group to another. However, there were considerable overlaps. No clear correlation was found between nuclear profile types and immunophenotypes. Cellular surface antigen patterns showed an extensive intra- and inter-case variability. The findings support the notion of a certain individuality of malignant B cell lymphomas and of a marked heterogeneity among their subtypes.

Adult↗
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↗