Resistivity coefficients for body composition analysis using bioimpedance spectroscopy: effects of body dominance and mixture theory algorithm.

Body composition is commonly predicted from bioelectrical impedance spectroscopy using mixture theory algorithms. Mixture theory algorithms require the input of values for the resistivities of intra-and extracellular water of body tissues. Various derivations of these algorithms have been published, individually requiring resistivity values specific for each algorithm. This study determined apparent resistivity values in 85 healthy males and 66 healthy females for each of the four published mixture theory algorithms. The resistivity coefficients determined here are compared to published values and the inter-individual (biological) variation discussed with particular reference to consequential error in prediction of body fluid volumes. In addition, the relationships between the four algorithmic approaches are derived and methods for the inter-conversion of coefficients between algorithms presented.

A continuous patient activity monitor: validation and relation to disability.

The measurement of patient activity over prolonged periods has been attempted with accelerometer-based devices, but these summate total acceleration and deceleration over time periods, are difficult to relate to recognizable activities and are influenced by passive movement. We describe the development of a portable monitor of ambulation. This logs posture (sitting, standing and lying) and number and vigour of steps in real time over prolonged periods, usually 24 h. This is based on a system of position sensors and an accelerometer which is sampled when the subject is standing. Data are processed through an interface and stored on a Psion Series 3 'palm top' computer. The system has been validated against observation, and the relationship of activity to disability in rheumatoid arthritis explored.

New laser Doppler scanner, a valuable adjunct in burn depth assessment.

A new medical instrument is presented that produces a doppler blood flow image from a laser beam in a raster pattern and the results of a pilot study which shows this technique to be highly accurate in assessing burn depth is described.

The study of plaques of psoriasis using a scanning laser-Doppler velocimeter.

A scanning laser-Doppler velocimeter, able to measure blood flux over a large area without contact with the skin surface, was used for the objective measurement of the vascular changes in psoriasis. Individual plaques were scanned, and tracings of the visible plaque edge taken on to a cellulose-acetate sheet from which area measurements were made using a digitizing tablet. Mean blood flux within plaques was increased fourfold compared with mean background flux. There was a highly significant linear correlation between plaque area measured by tracing and scanning, but area measured by scanning was greater. Detailed study of blood flux outside the visible plaque edge with the scanner, and with a conventional laser-Doppler instrument, showed this was due to a 2-4 mm rim of increased blood flux around plaques. The scanning laser-Doppler velocimeter allows rapid measurement of psoriasis in terms of mean blood flux and area of increased blood flux, and should be useful in the assessment of psoriasis severity and the response to treatment.

Quantification of contact allergic inflammation: a comparison of existing methods with a scanning laser Doppler velocimeter.

Responses to a range of doses of common contact dermatitis-producing allergens were measured using a novel scanning laser Doppler velocimeter and three commonly used conventional measurement techniques. The techniques were compared in terms of sensitivity, measurement error, range of the linear portion of the dose-response curve and ease of use. The detection thresholds of the objective methods did not differ significantly and did not detect responses at concentrations less than those required to produce a visible response. Of the objective methods the range of linearity was greatest when reactions were measured using change in skin fold thickness, erythema or area of inflammation. Measurement error was greatest with measurements made using the conventional laser Doppler velocimeter. Present instrumental methods are no more sensitive than visual assessment in the reading of patch test reactions. The conventional laser Doppler velocimeter was least suited for measurement of allergic contact hypersensitivity reactions as readings are time-consuming, show detectable changes over a more limited range of allergen concentration, and have a larger measurement error than the other methods. There is no single best method for measuring allergic contact hypersensitivity reactions. Useful data over a wide range of allergen concentrations can best be obtained by measurement of skin fold thickness, erythema or area of reaction using the scanning laser Doppler velocimeter. The scanning laser Doppler velocimeter has the added advantages of being able to measure area of reaction without contact with the skin surface and to measure reactions at all skin sites.

Measurement of cutaneous inflammatory reactions using a scanning laser-Doppler velocimeter.

The performance of a new scanning laser-Doppler velocimeter (LDV), which can rapidly measure blood flux over a large area of skin without contact with the skin surface, was compared with that of a conventional laser-Doppler instrument. The vascular response was measured to a range of doses of UVB, and dilutions of contact allergens and sodium lauryl sulphate. The detection threshold of the scanning LDV was equal to, or lower than, that of the conventional instrument. For allergic contact hypersensitivity reactions (ACH), the coefficient of variation was significantly less using the scanning LDV. The scanning LDV allowed accurate measurement of the change in area that occurs with increasing intensity of inflammatory reaction. For ACH reactions the area of inflammation continued to increase at dilutions where blood flux had reached a plateau. The flare area was found to increase linearly with log dose of histamine with no change in blood flux.

A laser Doppler scanner for imaging blood flow in skin.

This paper describes a novel medical instrument that produces an image of blood flow in the capillaries under the skin surface. A laser beam is used to detect blood cell motion from the Doppler broadening of the laser light scattered from the skin. The image is generated by scanning the laser beam in a raster. The design of a practical clinical instrument is outlined and some preliminary results are presented.

Laser Doppler flowmetry and bone blood flow in an isolated perfused preparation.

A preparation of an isolated bovine forefoot was established which could be perfused with blood at variable rates. A laser Doppler flowmeter probe inserted into the cancellous bone of the metatarsal produced a signal which varied with changes in perfusion rate and oscillated in synchrony with the peristaltic perfusion pump. A stronger laser Doppler signal was obtained when the probe was inserted into a drill hole than when inserted into a hole bored with a guide wire. It appears that laser Doppler flowmetry has potential intraoperative use when the viability of bone is in question.

A comparison of measurements of cerebral blood flow in the rabbit using laser Doppler spectroscopy and radionuclide labelled microspheres.

Laser Doppler spectroscopy has been evaluated for the measurement of cerebral blood flow (CBF) by correlation with simultaneous measurements by radionuclide labelled microspheres. The experimental procedures were carried out on five anaesthetised rabbits. The cortical tissue was exposed by means of a small burr hole and illuminated by a helium neon laser (632.8 nm). Reflected light was detected using a silicon photodiode, and CBF was calculated continuously from the power of the frequency weighted Doppler spectrum in the reflected light. Three successive measurements of CBF were made using the microsphere technique. Following an initial baseline measurement, CBF was increased by an infusion of metaraminol and then reduced by controlled haemorrhage. Laser Doppler spectroscopy provided continuous monitoring of blood flow fluctuations and during the haemorrhage it was possible to demonstrate CBF autoregulation until the mean blood pressure fell below 6.7 kPa (50 mmHg). A regression analysis was performed between the simultaneous CBF measurements from the two techniques using a least squares best fit straight line analysis (r = 0.92, P less than 0.001). It was concluded that the flow computed from laser Doppler spectroscopy varied linearly with CBF and offers the unique advantage of continuous and instantaneous measurements even during nonsteady state flow.