Delivery of medication by iontophoresis to treat post-burn hypertrophic scars: investigation of a new electronic technique.

At present, direct current (DC) and pulsed direct current (PDC) methods are used for iontophoresis. Although the DC field has high efficiency, it exhibits some side-effects. The PDC field has little side-effects, but the efficiency is lower. In this study, a new iontophoretic drug device was designed for providing the maximal efficiency with the minimal side-effects. Tests of animal and human models showed that the permeation rate of the new field was higher than that of PDC and DC fields, and side-effects were lower than that of the DC field.

On-line respiratory artefact removal via adaptive FIR filters in rheopneumographic measurement.

Impedance rheopneumography is a simple non-invasive technique that can reflect the vascular condition in the human pulmonary circulatory system. However, the much larger and almost in-banding respiratory artefact present has greatly restricted its usefulness to only respiratory patients of a less severe type, in view of the existing practice of requiring the subject to stop breathing momentarily during measurement. Conventional fixed or adaptive filtering cannot satisfactorily remove the artefact in view of the non-time stationary characteristic of the latter. In the paper, a fast adaptive FIR filter design method, which is based on the filter coefficient look-up table (CLT) concept, is presented as a solution. The CLT is constructed with the coefficients indexed to the cut-off frequency to separate the two components of the plethysmogram. An on-line fast Fourier transform is calculated to track the cut-off frequency. This filter can adaptively change its coefficients, not only for different subjects, but also for the same subject during long-term monitoring. Results show that this filter design is capable of providing an almost respiratory artefact-free signal for a majority of patients. The high speed of implementation also renders it a possibility for real-time monitoring applications.

Circuit model-based analysis of the impedance rheopneumogram.

Impedance rheopneumography, like other applications of electrical bio-impedance, is receiving increasing attention as a simple, non-invasive tool for clinical diagnosis of the pulmonary circulation. However, one major drawback of this method lies in the difficulty in computing accurately the time domain parameters therefrom for diagnostic purposes. This paper presents a model-oriented analysis technique based on physiological consideration of both the arterial and venous pathways of the pulmonary circulatory system. The technique involves a combination of a two-segment model and a modified form of the 'Windkessel' model, the summed response of which is curve-fitted to measurement data via the non-linear method of Marquardt to obtain the system parameters. A simple illustrative application is also given to explain the changes in wave morphology for a subject under measurement in the supine and sit-up positions. The result suggests that this technique shows promise of providing useful physiological information and better insight of system behaviour than existing technique.

Real-time drift suppressor for ECG.

By introducing poles close to the zeros of the transfer function (1 - Z-N), a drift filter is formed which involves only simple addition and shifting operations and is therefore capable of real-time application with moderate speed microprocessors. A normal ECG with moderate baseline fluctuations showed satisfactory drift suppression with minimal observable T-wave distortion.

Real time microprocessor-based 50 Hz notch filter for ECG.

High performance analogue notch filters are difficult to realize in practice. Their real time digital counterparts, when implemented on an inexpensive microprocessor with no additional hardware, also have limitations of their own. To overcome these limitations, we have developed a new type of 50 Hz notch filter with its poles close to the zero of the transfer function 1 + Z-N. This new type of digital notch filter can be used for suppression of 50 Hz noise in the ECG. The filter is simple to design and easy to implement on most 8-bit microprocessors. It has a high execution speed, low analogue to digital noise, low recursive noise and good frequency response with no overshoot or ringing. It is capable of suppressing 50 Hz noise by at least 40 db. Its finite bandwidth of 4 Hz causes about 2% attenuation on the QRS peak, which is acceptable for almost all practical applications. One possible drawback is that multiple notches occur at higher frequencies. However, this has hardly any effect on the ECG because of the limited notch bandwidth.

Pressure therapy in the treatment of post-burn hypertrophic scar--a critical look into its usefulness and fallacies by pressure monitoring.

Pressure therapy is generally accepted as the best noninvasive means of preventing and controlling hypertrophic scarring after burn injury. Most studies in the past have failed to correlate clinical response with magnitude of the garment-scar interface pressure. This study looked critically at our usual techniques of pressure therapy using pressure 'sensors' manufactured locally and based on electro-pneumatic principles. Many pitfalls, such as large variations of pressure at different geometric sites on the body, elastic deterioration in garments, problems of garment manufacture, and the unfavourable properties of the Lycra garments, were observed. Recommendations on pressure treatment were made based on our experiences, to improve the present technique of pressure therapy. These included the standardization of measurement techniques and garment tailoring, the regular checking of pressure at the garment-scar interface using pressure transducers, the appropriate garment adjustments, a strict regimen for garment wearing, and the intelligent use of pressure-padding and reinforcement. Areas of further research are also discussed.

Frequency dispersions of human skin dielectrics.

The electrical properties of many biological materials are known to exhibit frequency dispersions. In the human skin, the impedance measured at various frequencies closely describes a circular locus of the Cole-Cole type in the complex impedance plane. In this report, the formative mechanisms responsible for the anomalous circular-arc behavior of skin impedance were investigated, using data from impedance measurements taken after successive strippings of the skin. The data were analyzed with respect to changes in the parameters of the equivalent Cole-Cole model after each stripping. For an exponential resistivity profile (Tregear, 1966, Physical Functions of Skin; Yamamoto and Yamamoto, 1976, Med. Biol. Eng., 14:151--158), the profile of the dielectric constant was shown to be uniform across the epidermis. Based on these results, a structural model has been formulated in terms of the relaxation theory of Maxwell and Wagner for inhomogeneous dielectric materials. The impedance locus obtained from the model approximates a circular are with phase constant alpha = 0.82, which compares favorably with experimental data. At higher frequencies a constant-phase, frequency-dependent component having the same phase constant alpha is also demonstrated. It is suggested that an approximately rectangular distribution of the relaxation time over the epidermal dielectric sheath is adequate to account for the anomalous frequency characteristics of human skin impedance.

A reliable method for locating electropermeable points on the skin surface.

A method employing solvent-activated tape electrode was adapted for locating electropermeable points, minimizing possible errors due to human and external factors. Measurements along two meridians on the forearm showed that these points were somewhat scattered about the conventional acupuncture loci and their observable occurrence was probably the result of localized thermal damage of the epidermis.