Critical reviews in bioengineering最新文献

A percutaneous device (PD) constitutes a foreign material penetrating through the skin. It provides a connection between an internal organ or cavity and an extracorporeal device. PDs serving a multitude of clinical and research purposes are described. Breakdown of the PD-skin interface relatively soon after implantation is the failure mode of all present devices. Using the pertinent literature the present understanding of the pathophysiology of PD-skin interface behavior is discussed: the peculiarity of epidermal healing, lack of biomaterials compatible to epidermis, and mechanical stresses at the interface, each independently and in combinations are considered causative to this failure. Clinical reports on various permanent PDs are presented and ongoing research efforts at various centers are discussed.

The separate but closely related topics of waveform estimation by filtering and information extraction by pattern recognition are covered in this review. Because of the low signal-to-noise ratio generally encountered in evoked potential research, a variety of filtering methods have been employed for improving waveform estimation. Initially the filtering was done with analog devices but with the availability of high performance minicomputers virtually all filtering is now done digitally. Filters of various types are considered. Among them are single and multiple channel Wiener filtering, Kalman filtering, minimum mean square error filtering, maximum signal-to-noise filtering, and several types of nonlinear filters. The application of adaptive filtering techniques is also considered. In recent years there has been a continual increase in the application of pattern recognition techniques to the processing of evoked potentials. The techniques are based on statistical decision theory and the underlying basis of these procedures is reviewed. The technique of linear stepwise discriminant analysis is considered as well as the use of general discriminant functions of linear and quadratic types. Applications of these procedures to psychophysiological testing are discussed with particular emphasis on auditory and visual event-related potentials.

Left ventriculography is used by cardiologists, surgeons, and pharmacologists. Cardiologists use it to assess ventricular function and to scan the results of longitudinal studies to follow the course of the patient. Surgeons employ the results to appreciate changes following surgery, as improvement postbypass, and to compare the effectiveness of alternative procedures or maneuvers. Pharmacologists examine the results to assess the consequences of drug administration. In patients with ischemic heart disease, left ventriculography is an indispensable adjunct to selective coronary arteriography, and it provides anatomic and functional information important for diagnosis and for predicting the outcome of the patient. Using the results from cine left ventriculography, it is possible to calculate the EDV, ESV, SV, and EF and thus to evaluate the pump function of the left ventricle objectively, quantitatively, and reproducibly. However, these measures indicate total left ventricular function. A more detailed analysis of the cine left ventriculogram can provide specific information about the impaired segments. Methods for measuring and calculating the volume changes of the entire left ventricle were described and illustrated with their clinical implementation. Five methods of determining regional myocardial wall motion were applied to a population of subjects with normal wall motion and to patients with abnormal wall motion. The method was chosen which agreed best with the visual assessment of the cine by experienced cardiovascular radiologists. Clinical applications of regional wall motion assessment were described. A computer-compatible data base was created for roentgen images of a normally and of an abnormally contracting left ventricle, and this data base was contributed to a national repository for computer-compatible data bases. An automatic pattern recognition method was used to determine whether regional wall motion was normal or abnormal, and it was able to distinguish between these two groups satisfactorily. Current trends in ventriculography were described. A bioengineering approach has been used to solve the problem of measuring and describing the wall motion of the left ventricle of the human heart. The approach has been applied to the analysis of the contraction of the whole ventricle, regional wall motion, and the temporal pattern of wall motion. The mathematical equations underlying the analysis have been given, explained, and illustrated with examples. The implementation of the analyses using computers was discussed. The assumptions and sources of error have received particular attention.

The metal electrode is the critical interface between a measuring or stimulating device and the entity to be measured or stimulated. Electricity flows through wires by electron flow. It flows through tissue or fluid by ion flow. To produce an ion from an electron, a chemical reaction is necessary. This reaction occurs within a micron of the metal surface. It is a different reaction for an anode than for a cathode. It usually depends much more strongly on the metal chosen for the electrode than on the fluid or tissue electrolyte in which the electrode is immersed. In all cases, the reaction pair is strongly dependent on the quiescent voltage level of the system and on the magnitude of the voltage excursions around that level. This presentation will attempt to discuss the above points from the viewpoint of the researcher/designer who must use such metal electrodes to make practical measurements or who must connect practical stimulating devices to biophysical systems. The interdisciplinary field we will be discussing is "biophysical electrochemistry", and careful examination of each of these four component fields is necessary.

Traditionally, neurologists have emphasized qualitative techniques for assessing results of clinical trials. However, in recent years qualitative evaluations have been increasingly augmented by quantitative tests for measuring neurologic functions pertaining to mental state, strength, steadiness, reactions, speed, coordination, sensation, fatigue, gait, station, and simulated activities of daily living. Quantitative tests have long been used by psychologists for evaluating asymptomatic function, assessing human information processing, and predicting proficiency in skilled tasks; however, their methodology has never been directly assessed for validity in a clinical environment. In this report, relevant contributions from the literature on asymptomatic human performance and that on clinical quantitative neurologic function are reviewed and assessed. While emphasis is focused on tests appropriate for evaluating clinical neurologic trials, evaluations of tests for reproducibility, reliability, validity, and examiner training procedures, and for effects of motivation, learning, handedness, age, and sex are also reported and interpreted. Examples of statistical strategies for data analysis, scoring systems, data reduction methods, and data display concepts are presented. Although investigative work still remains to be done, it appears that carefully selected and evaluated tests of sensory and motor function should be an essential factor for evaluating clinical trials in an objective manner.