摘要:

Two geometrically identical models of the leaflets of a bicuspid bioprosthetic heart value have been constructed using finite elements. The boundary conditions applied to the models were also identical but a linear material model has been used in one and a nonlinear elastic model in the other. The models were full-scale and contained 2600 Belytschko-Lin-Tsai shell elements which allowed the variation of stress through the thickness of the leaflet to be modelled. A time-varying, spatially-uniform pressure differential was applied across the leaflets to model their behaviour during a complete cardiac cycle. The simulation was performed using a dynamic, explicit, time-stepping, finite element code. A comparison of the two models showed that the nonlinear model was more responsive to the time-varying pressure wave, and deformed into more complex shapes during the opening and closing phases which induced lower compressive but higher tensile stresses in the leaflets.

ISSN:0309-1902    

DOI:10.3109/03091909609008387

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Peripheral pulse waveforms can become stretched and damped with increasing severity of peripheral vascular disease (PVD) and hence could provide valuable diagnostic information. This study compares the diagnostic performance of 3 established classification techniques (a linear discriminant classifier, a k-nearest neighbour classifier, and an artificial neural network) for the detection of lower limb arterial disease from pulse waveforms obtained using photoelectric plethysmography (PPG). Pulse waveforms and pre- and post-exercise Doppler ultrasound ankle to brachial pressure indices (ABPI) were obtained from patients attending a vascular measurement laboratory. A single PPG pulse from each big toe was recorded direct to computer, pre-processed, and then used as classifier input data. The correct classzer outputs were the corresponding ABPI diagnostic classification. Pulse and ABPI measurements from 100 legs were used as training data for each classifier, and the computed classifications for pulses from a further 266 legs were then compared with their ABPI diagnoses. The diagnostic accuracy of the artificial neural network (80%) was higher than for the optimized k-nearest neighbour classifier (k= 27, accuracy 76%) and the linear discriminant classifier (71 %). TheKappameasure of agreement which excludes chance was highest for the artificial neural network (57%) and significantly higher than that of the linear discriminant classifier (Kappa40%, p<0.05). The value ofKappafor the optimized k-nearest neighbour classifier (k= 27) was intermediate at 47%. This study has shown that classifiers can be taught to discriminate between small, and perhaps subtle, differences in features. We have demonstrated that artificial neural networks can be used to classify arterial pulse waveforms, and can perform better overall than k-nearest neighbour or linear discriminant classifiers for this application.

ISSN:0309-1902    

DOI:10.3109/03091909609008388

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The electrical impedance parameters of human blood, that is, plasma resistance Rp, cell interior resistance Ri;and cell membrane capacitance Cm, were determined by measuring impedance amplitudes at three different frequencies, 0 1, 0.8 and 1.2 MHz. Several new findings have been obtained. The fibrinogen in normal blood raised Rp, and Cm, by about 4 % and 20%, respectively, and serum proteins contributed to the capacitance by about 14 %. The results imply that the electrical impedance of blood may reject certain diseases that involve abnormal compositions of certain plasma proteins. Measurement on 62 samples with various erythrocyte sedimentation rates (ESR) demonstrated that both Rp, and Cm, were proportional to ESR, implying that the impedance measurement might be an alternative method for quick estimation of ESR. Duringin vitrostorage of blood at 4°C, both Rp, and Cm, decreased with time, about−20% for Cm, after four weeks J storage. The results imply that the impedance change might be a useful index for evaluating the quality of stored blood.

ISSN:0309-1902    

DOI:10.3109/03091909609008389

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Lumin is a potent cell-activating agent and a photosensitizer characterized by absorption peaks at 670 nm and 770 nm. It has already been demonstrated that macrophase activity is enhanced greatly by lumin administration with laser light irradiation and that this method is useful in cancer immunotherapy. In this study, a new needle type therapeutic system was developed for the immunotherapy of cancer growing in deep human organs. A human lung cancer grafted onto nude mice was strongly cicatrized by collagen fibres about four weeks after the first treatment. The collagen fibres seemed to seal-off the tumor and prevent its growth with intense cicatrization. In addition, a high T/B cell ratio of lymphocytes was observed in the peripheral blood of the treated mice, although the thymus is congenitally absent from nude mice. These results demonstrated that the system is a reliable method for cancer treatment in deep organs without side effects andor major surgical intervention.

ISSN:0309-1902    

DOI:10.3109/03091909609008390

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

A study has been carried out of the RF feld strength around a total of 17 patients undergoing radio-frequency endometrial ablation in three hospital centres. The mean equivalent power density at the position of the surgeon exceeded 10 Wm−2, which is the derived investigation level for exposure to electromagnetic fields. This value is derived from a basic restriction in the average specific absorption rate in the body to 0.4 Wkg−1. This limit applies to general population as well as occupational exposure and is well below that which has been shown to be hazardous to health. Also, the working conditions did not place physical stress on the surgeon. The maximum value of the specific energy absorption rate in the head or trunk should not exceed 10 Wkg−1. Measured values on the field strength suggest that this organ dose limit was not exceeded. It is concluded that staff exposure to stray RF radiation during radio-frequency endometrial ablation is not considered to be hazardous to health.

ISSN:0309-1902    

DOI:10.3109/03091909609008391

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The paper describes and analyses a method for locating metal implants bared on the interaction of a conductive object with a weak alternating magnetic field. Theoretical values for the boundary of detectability and the boundary of localability are introduced to show some technical characteristics, the diagnostic feasibility and limitations of the method. Clinical experiences aye described in order to compare the theoretical expectations with practical results Several advantages of the proposed diagnostic method an terms of inexpensive instrumentation, ease of operation and sensitivity are discussed

ISSN:0309-1902    

DOI:10.3109/03091909609008392

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The Biomedical Engineering HandbookEditor in Chiek joseph D. Bronzino (CRC Press Inc, 1995), pp. 2862. Price f95, ISBN 0 8493 8346 3.Safety in Diagnostic RadiologyEdited by K. Faulkner, A. P. Jones and A. Walker. The Institute of Physical Sciences in Medicine Publications (York, UK), 1995), pp. 126. Price f22.00. ISBN 0 904181 812.Digital EEG in clinical practiceBy Peter K. H. Wong (Lippincott-Raven, 1995), pp. 316. Price 265.50, ISBN 0-397-51635-5.Physiological Monitoring and Instrument Diagnosis in Perinatal and Neonatal MedicineEdited by Yves W. Brans and William W. Hay Jr, Cambridge University Press, Cambridge, 1995, 580.00, pp. 385. ISBN 0-521-41951-4

ISSN:0309-1902    

DOI:10.3109/03091909609008393

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor