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Biomedical subjects

C G Ellis

Publications and source records attributed to C G Ellis.

At least 55 records · Page 3Linked to original sources
PubMed1985

The present and future role of general practice surgery.

In the RSA a general practitioner may perform any operation he feels competent to do. This contention is discussed, the type and frequency of operations performed by GPs is described, and the changing role of general practice surgery, its medicolegal implications, and the experience and training needed are outlined.

Clinical Competence↗
PubMed1985

Simultaneous assessment of red cell perfusion in skeletal muscle by laser Doppler flowmetry and video microscopy.

The objective of this study was to compare temporal and spatial variations of the laser Doppler flowmeter output (V) with the corresponding variations of perfusion (cells/mm3 X mm/s) evaluated by video microscopy. The flowmetry and video microscopy sampled 2 mm3 (approx.) and 0.84 mm3 surface volumes of the sartorius muscle in anesthetized frogs, respectively. The overall ranges of the output and perfusion measurements were from 0.01 to 0.72 V and from 45 to 1404 cells/mm3 X mm/s. Within these ranges, temporal variations induced by muscle contraction correlated well (overall r = 0.91), but the spatial variations associated with the resting state correlated poorly (overall r = 0.45). When the penetration of the laser light was limited to 0.3-0.4 mm (to make the volumes sampled by both techniques more comparable) the overall r of the spatial comparison increased to 0.86. It is concluded that the flowmeter (1) is affected by red cell perfusion below the tissue depth of 0.3-0.4 mm, and (2) can follow both the temporal and spatial variations of red cell perfusion in the tissue examined.

Capillaries↗
PubMed1984

The contract in medical partnership.

You may spend more time with your partner than with your wife; if you wish to have and to hold from this day forward then read the partnership contract carefully and understand its implications. A review of the main points and pitfalls is given to help the practising doctor draw up and check a contract.

Financial Management↗
PubMed1984

Measurement of the lineal density of red blood cells in capillaries in vivo, using a computerized frame-by-frame analysis of video images.

In order to study the oxygen supply system within a capillary bed it is desirable to know the lineal density of red blood cells (RBCs) in individual capillaries; viz number of cells per millimeter. We have developed a video computer method for "continuous" measurements of lineal density, based on frame-by-frame analysis of the spatial-average of blood opacity over a selected length of capillary. Each capillary is calibrated separately, in order to determine the relationship between mean opacity and lineal density for that vessel. Since the method does not attempt to detect individual RBCs, it can be applied to capillaries with RBCs which overlap each other to some extent. Also, since the opacity data is normalized with respect to "background" light intensity and "contrast," this technique can be applied to thick tissues such as skeletal muscle. The method has been tested on capillaries in frog sartorius muscle and is able to predict, on average, the number of frog RBCs in an 80-micron length of capillary to +/- one-quarter cell. At present, computation times limit "real time" measurement of lineal density to a sampling rate of 10 sec-1. The data may also be used (1) to compute red cell flux (cells X sec-1), if corresponding velocity measurements are available, and (2) to estimate capillary hematocrit.

Animals↗
PubMed1983

Television-computer method for in vivo measurement of capillary diameter, based on the passage of red cells.

Capillary diameter is generally measured by methods requiring a trained observer to determine the location of the vessel walls. We have developed a video computer method for measurement of capillary diameter, based on temporal fluctuations of light intensity within the lumen due to the passage of red cells. These fluctuations are quantified, at successive points along a line perpendicular to the capillary by sampling, with a microcomputer, the output of a video analyzer and calculating the variance of light intensity with time at each point. A profile of this variance, across the vessel, shows an abrupt change at each edge of the flowing red cell column. The edge of the lumen is "defined," for the computer program, as the last point before the variance of light intensity becomes significantly greater than in the surrounding tissue. The method thus assumes there is no detectable cell-free plasma layer adjacent to the vessel wall. Both in vitro and in vivo tests showed good agreement between luminal diameters measured by a trained observer and by the video computer method. Each diameter measurement requires 2.5 sec for data acquisition and 0.3 sec for computation. This automated technique applies a standard criterion to the measurement of capillary diameter and thus avoids subjective error. It may be used for sequential measurements, e.g., where the microvessel diameter is changing with time.

Animals↗
PubMed1983

Heterogeneity of capillary diameters in skeletal muscle of the frog.

Capillary diameters in sartorius muscle of frogs were measured in vivo by means of a new computer video method, based on the passage of red blood cells (RBCs) through the capillary (C. Ellis, R. Sanfranyos, and A. Groom (1983), Microvasc. Res. 26, 139-150). The distribution of capillary diameters from 21 frogs was represented by a histogram with a mean +/- SD of 16.7 +/- 4.4 microns (N = 83). The measured dimensions (mean +/- SD) of frog RBCs, which have a flattened ellipsoidal shape, were: major axis = 24.1 +/- 2.6 microns (N = 149); minor axis = 16.5 +/- 1.5 microns (N = 158); thickness at center = 5.4 +/- 0.8 microns (N = 32). Frog RBCs travel through capillaries with their major axes predominantly parallel to the direction of flow; therefore, RBCs pass through capillaries without deformation provided that the diameter of the capillary is larger than the minor axis of the cell. By standardizing the measured values of capillary diameter in terms of mean minor dimension of the RBCs (ratio of means for frog being 1.0, approx), we were able to compare the diameter distribution in an amphibian with that in a mammal (rat). If RBC size alone mattered, both standardized distributions should superimpose; however, that for frog was shifted to the right of that for rat, indicating that frog RBCs are less deformable than RBCs of rat. This highlights the necessity, in the microcirculation, for matching capillary diameter to both size and deformability of the red cell.

Animals↗
PubMed1982

Evaluation of the flying spot technique as a television method for measuring red cell velocity in microvessels.

The success of measuring red cell velocity in microvessels by television methods based on cross-correlation depends to a considerable extent on the optical contrast between red cells and plasma gaps passing through these vessels. Poor optical contrast, such as under conditions of low magnification, may result in deteriorated cross-correlograms and, consequently, in completely erroneous velocity values. The success of measuring velocity by the flying spot technique, however, depends only on the operator's ability (1) to discern the moving red cells, and (2) to match the speed of the spot to that of these cells. We have implemented this technique as a television method and estimated the subjective error involved in this velocity matching. Under a total magnification of 112 X, the estimated relative errors among four observers in the velocity range from 0.10 to 0.57 mm/s varied between 4.4 and 14.9%, while the overall error was 8.7%. It was concluded that this technique can provide, in the range from 0 up to possibly 1-2 mm/s, quick and reliable velocity measurements with a reasonable accuracy. Also, since no sophisticated equipment is required for the implementation, this method, at present, is much less expensive than the other conventional television methods for measuring velocity.

Animals↗
PubMed1978

Delayed flow of patients in a Black hospital.

Two hundred consecutive patients who were discharged from a ward in a Black hospital were studied with reference to delay of flow through a system. Problems are discussed, e.g. that of the young patient, admitted at night, who awaits radiography and investigations. Because he is unable to give consent, he must wait for an operation until appropriate staff and consent are available. He recovers, may have to wait for a surgical appliance, is discharged and may then have to wait several more days before relatives collect him. The unique problems in Black hospitals can be alleviated, inter alia, by departmental admission protocols, outpatient liaison education officers, more even distribution of medical manpower, improved hospital transport systems and overnight stay wards incorporated in a more active outpatient system to replace the present sorting system.

Black or African American↗
PubMed1975

Ability of man to detect increases in his breathing.

The ability of four normal subjects to detect increases in their ventilation was studied at rest and at two levels of exercise using a raised inspired Pco2 to further increase ventilation. Subjects signaled when the increase in ventilation was recognized. The average tidal volume (VT) at rest was 520 ml with a frequency of 14; these values increased to an average of 3,300 ml and 21 at the highest work load. There was no significant change in frequency with CO2. Detection occurred when the tidal volume increased by 700 ml (varying 550-890 between subjects but constant for any one subject at the three levels of ventilation.) Thus the appreciation of increase is proportionately more sensitive at higher levels of ventilation. Experiments in which the ventilation was increased by hypoxia or by following a visual demand, and observations of other sensations (oral, cerebral) indicate that the increase in vetilation is recognized through increased breathing rather than awareness of ventilatory stimuli.

Adult↗