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Biomedical subjects

W F Walker

Publications and source records attributed to W F Walker.

At least 19 recordsLinked to original sources
PubMed1988

Amputation for peripheral vascular disease: the case for level selection.

One hundred major lower limb amputations were performed for end stage peripheral vascular disease over a 15-month period. Selection of amputation level was made on the basis of laboratory criteria using skin blood flow and infrared thermography data. Eighty-one amputations were performed at the below-knee level with six failures. This resulted in a final below-knee: above-knee amputation ratio of 3:1. It is clear that there are still many centres in the UK where above-knee amputation is the accepted operation, despite the inherent drawbacks to this procedure. We recommend that more attention is given to achieving higher below-knee amputation rates to improve the chances of amputee mobility and therefore quality of life.

Amputation, Surgical↗
PubMed1988

Sibling incest.

Explore the source record for details and available documents.

Child↗
PubMed1988

Further experience in the healing rate of lower limb amputations.

Results of lower limb amputation in the Tayside Region in the years 1981-1985 have been analysed. Three-hundred and twenty-four amputations were performed on three-hundred and eight patients. Two-hundred and thirty-six amputations were attempted at the below-knee level. Only 19 required proximal revision. Prior to amputation, all patients should have a detailed vascular assessment, and the operation should be performed by experienced amputation surgeons using meticulous technique.

Adult↗
PubMed1987

Fate of the vascular patient after below-knee amputation.

50 below-knee amputations were carried out in 45 patients (25 men and 20 women), mean (SD) age 73 (10.5) years. The mean survival time was 22(16) months after the operation. In each patient the healing potential of a below-knee amputation was determined preoperatively by segmental pressure studies and thermographic delineation of skin perfusion. 33 of the stumps healed by first intention, in 14 healing was delayed but occurred without the need for further surgery, and 3 stumps healed after local wedge excision. The initial mobilisation rate was 90%. Thus, there are no grounds for carrying out an initial above-knee amputation to save the patient a further operation.

Aged↗
PubMed1987

Role of oxygen in the production of human decompression sickness.

In the calculation of decompression schedules, it is commonly assumed that only the inert gas needs to be considered; all inspired O2 is ignored. Animal experiments have shown that high O2 can increase risk of serious decompression sickness (DCS). A trial was performed to assess the relative risks of O2 and N2 in human no-decompression dives. Controlled dives (477) of 30- to 240-min duration were performed with subjects breathing mixtures with low (0.21-0.38 ATA) or high (1.0-1.5 ATA) Po2. Depths were chosen by a sequential dose-response format. Only 11 cases of DCS and 18 cases of marginal symptoms were recorded despite exceeding the presently accepted no-decompression limits by greater than 20%. Analysis by maximum likelihood showed a shallow dose-response curve for increasing depth. O2 was estimated to have zero influence on DCS risk, although data variability still allows a slight chance that O2 could be 40% as effective as N2 in producing a risk of DCS. Consideration of only inert gases is thus justified in calculating human decompression tables.

Decompression Sickness↗
PubMed1986

Oxygen inhalation induced changes in the skin as measured by transcutaneous oxymetry.

Transcutaneous oxygen (PtcO2) measurements were made on 46 patients with severe ischaemia of the lower limbs and on 17 age-matched controls. Values breathing air, 100 per cent oxygen and the rate of change of PtcO2 breathing oxygen were recorded. Of 29 below knee amputations there were 4 failures; 16 had PtcO2 values less than 35 mmHg, but 12 of the 16 healed. When the rate of change of PtcO2 during oxygen inhalation was greater than 9 mm Hg/min all below knee amputations healed; all 4 failures were found to have values less than 9 mm Hg/min while only one patient with a value of less than 9 mm Hg/min healed a below knee amputation. This study shows that low PtcO2 values are a poor indication of healing potential. A more reliable index of skin viability is provided by the dynamic measurement of PtcO2 changes during oxygen inhalation. The addition of an oxygen inhalation test, when making PtcO2 measurements, greatly enhances the applicability of the technique in the assessment of the oxygen supply to the skin.

Aged↗
PubMed1986

Arterial systolic pressures in critical ischemia.

Segmental systolic pressures were measured in a group of patients with clinically irreversible ischemia. There was a good relationship between the level of pressure in a limb and the eventual outcome, but a particular level of pressure was found to be a poor indicator of a specific level of viability. These results support previous concern about the limitations of systolic pressure measurements in determining the level of limb viability. We suggest that local intrinsic regulation of the microcirculation plays a major role in the ultimate survival of tissues in an ischemic limb.

Aged↗
PubMed1986

pH changes in the dermis during the course of the tuberculin skin test.

The response of six healthy young adults to tuberculin skin testing was studied. Five subjects developed a typical delayed-type hypersensitivity reaction to PPD with a local rise in skin temperature, and the sixth showed a less intense response; a considerable increase in blood flow velocity was seen in all reactions. All subjects showed a fall in pH in the dermis during the course of the reaction: in four subjects the pH minimum occurred at the time when the changes of erythema and induration were most prominent, in one subject the pH fall preceded the maximal clinical changes, and in the remaining subject a substantial fall in pH occurred with only transient erythema. It was concluded that the local tissue acidosis had resulted from the greatly increased metabolic demand of the lymphocytes and monocytes attracted into the dermis as part of the type IV delayed-type hypersensitivity reaction, and that the concurrent reactive hyperaemia was insufficient to clear the acidic metabolic products of the greatly increased cell population.

Adult↗
PubMed1985

Circumferential skin blood flow measurements in the ischaemic limb.

Skin blood flow (SBF) values were estimated on the posterior, medial and lateral aspects of the lower leg in 47 patients presenting for assessment of amputation level. Measurement was made using a radioisotope (iodoantipyrine) clearance technique. Medial SBF was 9.0 +/- 5.2 ml 100 g-1 min-1; posterior SBF was 8.3 +/- 5.0 ml 100 g-1 min-1 and lateral SBF was 6.5 +/- 4.1 ml 100 g-1 min-1. The results gave significantly higher SBFs on the medial and posterior aspects of the ischaemic leg. The finding of an uneven distribution of blood flow at the below knee amputation level has important implications in the planning of amputation flaps.

Aged↗
PubMed1985

5 S and 5.8 S ribosomal RNA sequences and protist phylogenetics.

More than 100 5 S 5.8 S rRNA sequences from protists, including fungi, are known. Through a combination of quantitative treeing and special consideration of "signature' nucleotide combinations, the most significant phylogenetic implications of these data are emphasized. Also, limitations of the data for phylogenetic inferences are discussed and other significant data are brought to bear on the inferences obtained. 5 S sequences from red algae are seen as the most isolated among eukaryotics. A 5 S sequence lineage consisting of oomycetes, euglenoids, most protozoa, most slime molds and perhaps dinoflagellates and mesozoa is defined. Such a lineage is not evident from 5.8 S rRNA or cytochrome c sequence data. 5 S sequences from Ascomycota and Basidiomycota are consistent with the proposal that each is derived from a mycelial form with a haploid yeast phase and simple septal pores, probably most resembling present Taphrinales. 5 S sequences from Chytridiomycota and Zygomycota are not clearly distinct from each other and suggest that a major lineage radiation occurred in the early history of each. Qualitative biochemical data clearly supports a dichotomy between an Ascomycota-Basidiomycota lineage and a Zygomycota-Chytridiomycota lineage.

Animals↗
PubMed1985

The effect of the transcutaneous electrode on the variability of dermal oxygen tension changes.

Transcutaneous oxygen measurements (TCPO2) are being used increasingly for the assessment of tissue viability in the ischaemic limb. The major objective with such a technique is to determine the critical level of TCPO2 which defines the boundary between skin viability and non-viability. To be able to do this, an assumption is made that measurements from different centres using various TCPO2 sensors are comparable. This study shows that static and dynamic changes of TCPO2 (air to oxygen breathing) made with two commercially available instruments are not directly comparable. We suggest that the physical characteristics of present TCPO2 electrodes are not optimal for measurements on adult skin. TCPO2 measurements made in conditions of skin ischaemia should be interpreted with caution because the ratio of local oxygen demand to blood flow is such that the measurement may be underestimated by TCPO2 electrodes with a high oxygen consumption.

Adult↗
PubMed1985

Quantitative assessment of the effectiveness of chemical lumbar sympathectomy.

Twenty-one chemical sympathectomies were assessed in this study by taking infra-red thermograms of the feet before and after the procedure. Patients with relatively high perfusion pressures were shown to have the best response, while those with a low perfusion pressure had little or no increase in mean temperature in the foot.

Aged↗
PubMed1985

A rationale for skew flaps in below-knee amputation surgery.

The use of thermography in the assessment of amputation levels has demonstrated a medial to lateral thermal gradient in many cases. In order to see whether this reflected a true medial to lateral skin blood flow gradient, a prospective study was set up to measure blood flow medially and laterally below the knee. Twenty-one patients, presenting for amputation assessment with end-stage peripheral vascular disease, were studied. Skin blood flows were measured using an intradermal radioisotope clearance technique. Results showed a highly significant difference between medial and lateral skin blood flows (t = 4.79; p less than 0.001). In view of the significantly higher blood flow in the medial skin of the lower leg, it is suggested that a more medially based posterior below-knee amputation skin flap may be of more value in some patients.

Aged↗
PubMed1984

The relationship between temperature isotherms and skin blood flow in the ischemic limb.

This study was conducted in order to establish a relationship between thermographically defined levels of viability in the ischemic limb and a measurement of skin blood flow. Color thermograms (10 colors, 0.6 degree C apart) defined the temperature gradient and skin blood flow was measured, using the radioactive clearance method in three discrete isotherms set 1.8 degrees C apart. The differences in skin blood flow measured in the three separate isotherms were significant (P less than 0.001). The results of this study support previously unqualified assertions that thermographic temperature gradients along an ischemic limb are indicative of local microcirculatory status. The potential of the thermographic method for demarcating viable and nonviable skin flaps at the chosen site of amputation is confirmed.

Aged↗
PubMed1984

Tissue oxygen tension in normal and ischaemic human skin.

Tissue oxygen tension has been measured in the skin of the lower limbs in ten normal subjects and in six patients with peripheral vascular disease. Measurements of oxygen tension breathing air, PO2(air) and breathing oxygen for 4 min, PO2(O2:4) were assessed in the thigh, below knee and foot levels of all subjects. In normal subjects PO2(air) and PO2(O2:4) values were (+/- SD) 4.9 +/- 0.8 kPa (37.2 +/- 6.1 mmHg) and 14.8 +/- 2.2 kPa (111 +/- 16.3 mmHg) respectively with no significant difference at any level. In ischaemic subjects PO2 (air) values were significantly reduced at the foot level but PO2(O2:4) values were significantly reduced at both below knee and foot levels. Our results suggest that the rise in oxygen tension following a change from air to oxygen breathing may be a better indicator of local blood flow conditions than a measure of the tissue oxygen tension by itself.

Adult↗
PubMed1984

Assessment of tissue viability in relation to the selection of amputation level.

Assessment of the optimum level of amputation of an ischaemic limb can be exceptionally difficult. For this reason there has been an intensive effort, particularly in the past 20 years, to find suitable non-invasive ancillary methods to aid in the amputation level selection. This paper reviews three separate research and development areas which have evolved simultaneously in our laboratory: skin partial oxygen pressure, skin blood flow, and infrared thermography. The physiological basis for each of these measurements is discussed along with the merits and demerits of each.

Amputation, Surgical↗