1,720,973 research outputs found
Nearest-neighbor analysis of spatial point patterns: application to biomedical image interpretation
No full textAnalysis 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
Impiego di tecniche CADCS per l'analisi e il controllo di dispositivi di assistenza cardiocircolatoria in serie
No full textA symmetrical computer model of nonlinear mechanical properties of the tracheobronchial airways
No full textA nonlinear time-domain simulator of the tracheobronchial tree is proposed to model breathing mechanics during artificial ventilation. It Is based on Weibel's symmetrical geometric lung description which divides the airways into 24 generations, characterised by increasing numbers of branches. The tracheobronchial tree is represented as a nonlinear RLC ladder network, reflecting the viscoelastic and inertial properties of each generation. The simulator is also used to reproduce intermittent positive pressure ventilation with constant inspiratory flow, widely used in intensive care. The simulator, implemented in MATLAB-SIMULINK, enables modelling of different physiopathological and ventilatory conditions, calculation of flow and pressure time courses and analysis of the viscoelastic behaviour of the various airway generations. Results obtained with the simulator clarify time changes in generation resistances during the breathing cycle. In particular, at the beginning of expiration, upper airway resistance increases and then decreases under the influence of time-varying flow and airway volume. Since lower airway resistance only depends on airway volume, it increases rapidly in the first phase of expiration and then remains almost constant
A naïve Bayes classifier for planning transfusion requirements in heart surgery
No full textRationale, aims and objectives Transfusion of allogeneic blood products is a key issue in cardiac surgery. Although blood conservation and standard transfusion guidelines have been published by different medical groups, actual transfusion practices after cardiac surgery vary widely among institutions. Models can be a useful support for decision making and may reduce the total cost of care. The objective of this study was to propose and evaluate a procedure to develop a simple locally customized decision-support system. Methods We analysed 3182 consecutive patients undergoing cardiac surgery at the University Hospital of Siena, Italy. Univariate statistical tests were performed to identify a set of preoperative and intraoperative variables as likely independent features for planning transfusion quantities. These features were utilized to design a naïve Bayes classifier. Model performance was evaluated using the leave-one-out cross-validation approach. All computations were done using spss and matlab code. Results The overall correct classification percentage was not particularly high if several classes of patients were to be identified. Model performance improved appreciably when the patient sample was divided into two classes (transfused and non-transfused patients). In this case the naïve Bayes model correctly classified about three quarters of patients with 71.2% sensitivity and 78.4% specificity, thus providing useful information for recognizing patients with transfusion requirements in the specific scenario considered. Conclusions Although the classifier is customized to a particular setting and cannot be generalized to other scenarios, the simplicity of its development and the results obtained make it a promising approach for designing a simple model for different heart surgery centres needing a customized decision-support system for planning transfusion requirements in intensive care unit
A geometric model analysis of conductive airways in expiratory flow limitation during artificial ventilation
No full textExpiratory flow limitation (EFL) was simulated in mechanical ventilation through a recently proposed tracheobronchial tree model which reproduces breathing mechanics in the time-domain using Weibel's symmetrical description of lung anatomy considered as 17 upper generations conducting air and seven deeper generations where gas exchange takes place. The model allows for flow turbulence, inertance and tissue viscoelasticity to be represented nonlinearly and distributed along the tracheobronchial tree in a lumped parameter description. An electric analogue of the simulator, consisting of a RLC ladder network, was numerically implemented by Matlab-Simulink software. Normal conditions and chronic obstructive pulmonary disease (COPD) were simulated by setting model parameters. An extra negative expiratory pressure (NEP) was introduced to detect EFL. The transmural pressures of conductive airways, their viscoelastic characteristics and their related distributions of transversal geometrical changes over the breathing cycle were evaluated. The results showed that during mechanical ventilation, large modifications in the elastic characteristics of the conductive airways explain EFL in simulated COPD. In particular, a marked expiratory reduction in medium bronchi diameter, up to 20-30% of their maximum value, and a progressive decrease in small bronchi diameter during expiration were observed. A remarkably lower reduction in medium bronchi diameter and almost constant behaviour of small bronchi diameter during expiration were found in the simulated healthy subject. Application of NEP confirmed the absence of EFL for normal cases whereas COPD was flow limited over most of expiration
Digital filtering of central venous pressure for evaluating intrapleural pressure changes during mechanical ventilation
No full textEffect of compliant intermediate airways on total respiratory resistance and elastance in mechanical ventilation
No full textTotal respiratory resistance and elastance were estimated off-line in a sample of 60 patients undergoing mechanical ventilation by means of two regression models in order to analyse and understand a possible physiological mechanism determining differences in inspiration and expiration. The first model considered a single value for resistance and elastance over a whole breathing cycle, whereas the second model considered separate values for inspiratory and expiratory resistance and a single value for elastance. Inspiratory resistance was found to be lower than expiratory resistance, and intermediate values were obtained for resistance estimated over the whole breathing cycle. Student's t-test showed a highly significant difference between these resistance estimates, and principal components analysis demonstrated a significant increase in information when both inspiratory and expiratory resistances were used. Minor differences were found between values of elastance calculated with the two approaches. In an attempt to interpret these experimental results, a lung model incorporating the non-linear viscoelastic properties of the intermediate airways was considered. This model suggested that changes in intermediate airway volume play a significant role in breathing mechanics during artificial ventilation and indicated that inspiratory and expiratory resistance could be useful parameters for locating airway obstruction
Instrumental measurement of skin colour and skin type as risk factors for melanoma: a statistical classification procedure
No full textA 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
- …
