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P Hua

Publications and source records attributed to P Hua.

8 recordsLinked to original sources
PubMed1992

Skin impedance measurements using simple and compound electrodes.

We have studied the effect of the electrode configuration on the measurement of body impedance and found that the electrode configuration greatly affects the impedance measurement using the four-electrode method. We studied the characteristics of the compound electrode and found that the compound electrode provides the four-electrode method in a compact form. A new method of measuring the skin impedance using simple electrodes at low frequencies was developed. At high frequencies where the effect of internal tissue impedance is not negligible, we used the compensation method using compound electrodes, because they measure the voltage right under the skin. At 50 kHz, we measured the real part of the skin impedance of less than 80 omega on the thorax. We propose a simple instrument which can measure accurate skin impedance at various frequencies.

Electric Conductivity↗
PubMed1992

Measuring lung resistivity using electrical impedance tomography.

We propose the use of electrical impedance tomography (EIT) imaging techniques in the measurement of lung resistivity for detection and monitoring of apnea and edema. In EIT, we inject currents into a subject using multiple electrodes and measure boundary voltages to reconstruct a cross-sectional image of internal resistivity distribution. We found that a simplified, therefore fast, version of the impedance imaging method can be used for detection and monitoring of apnea and edema. We have showed the feasibility of this method through computer simulations and human experiments. We speculate that the EIT imaging technique will be more reliable than the current impedance apnea monitoring method, since we are monitoring the change of internal lung resistivity. However, more study is required to verify that this method performs better in the presence of motion artifact than the conventional two-electrode impedance apnea monitoring method. Future work should include experiments which carefully simulate different kinds of motion artifacts.

Adult↗
PubMed1992

Mass culture of anchorage-dependent animal cells with newly born calf skin collagen membrane and microcarrier.

It was shown that collagen substrate enhances the growth as well as the differentiation of many cells in culture. Collagen is one of the major fibrous proteins of animal bodies and the pure collagen used in this experiment was extracted from the newly born calf skin by chemical and biochemical methods. The analytical results obtained by ion-exchange chromatography and electrophoresis showed that the main components of denatured collagen were alpha monomers and beta dimers. The collagen and denatured collagen membranes were prepared by coating their solution on peteri dishes. Various types of cells were cultured on these membranes after being irradiated by ultraviolet ray. The denatured collagen was proved a good substratum for culturing anchorage dependent cells. A denatured collagen (gelatin) microcarrier, GT-2 was obtained by cross-linking gelatin with glutaraldehyde in a suspension polymerization process. These microcarriers were used successfully to culture various anchorage-dependent cells such as Vero, CHO, Bowes and fish cells in varying scales, including T-flasks, spinning bottles, revolving bottles and 1.5 l and 20 l bioreactors.

Animals↗
PubMed1988

Three-dimensional reconstruction in electrical impedance tomography.

We have developed a three-dimensional, computer-simulated, electrical impedance tomographic imaging system using the four-electrode measurement technique. The reconstruction process finds the numerical solution of Laplace's equation by using the finite element method and the Newton-Raphson algorithm. A new diagonal electrodes measurement method provides lower error than the usual neighbouring electrodes measurement method. For a three-layer, 4 x 4 model, the number of iterations increased from 3 to 16 as the number of randomly placed, high-resistivity voxels increased from 3 to 18.

Electric Conductivity↗
PubMed1988

A regularised electrical impedance tomography reconstruction algorithm.

The Newton-Raphson algorithm is an effective reconstruction method. However, it exhibits degraded performance for ill-conditioned problems, especially in the presence of measurement error. This paper uses the regularisation method to improve the system's conditioning, which stabilises the reconstruction method. It shows that the [[ p'' ]] penalty form yields superior images, as compared to the [[ p ]] penalty form.

Algorithms↗