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Biomedical subjects

V A Spence

Publications and source records attributed to V A Spence.

At least 37 records · Page 2Linked to original sources
PubMed1988

The effect of prazosin on skin microcirculation as assessed by laser Doppler flowmetry.

1. Laser Doppler flowmetry was used in six normal volunteers to record changes in fingertip skin blood flow after the administration of prazosin to block postsynaptic alpha 1-adrenoceptors. 2. Prazosin (0.5 mg orally) did not alter systolic or diastolic blood pressure or heart rate. 3. Prazosin did significantly increase basal skin blood flow 2 h after its administration but this effect was no longer evident after contralateral hand warming. Prazosin markedly reduced the skin vasoconstrictor response to deep inspiration and to contralateral hand cooling. 4. This study suggests that postsynaptic alpha 1-adrenoceptors are involved in maintaining skin vasoconstrictor tone at rest and are also involved in the rapid skin vasoconstriction seen in response to a deep inspiration and to contralateral hand cooling.

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↗
PubMed1986

Measurement of skin swelling in the tuberculin test by ultrasonography.

A new method is described for non-invasive measurement of the thickness of the skin at the site of a skin test from the echo pattern of a pulsed ultrasonic (15 MHz) A-mode scanner. In tuberculin tests on normal volunteers, the skin thickness increased rapidly during days 1 and 2 and was usually greatest at day 4. The echogram measurements can be used to calculate the increase in skin volume and this is disproportionately greater than would be expected from measurements of the diameters of erythema and induration.

Adult↗
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

Patterns of blood flow in the microcirculation of the skin during the course of the tuberculin reaction in normal human subjects.

Digital thermographic imaging and laser-Doppler velocimetry techniques were used to study the sequence of microcirculatory changes in typical Type IV (DHS-type) skin reactions to intradermal injection of PPD into seven healthy tuberculin-positive subjects. Thermography has shown that there is very little change in thermal status at 6 hr, that there is an area of raised temperature roughly corresponding to that of erythema around the site of antigen injection at 24 hr, and that the area of 'hot' skin starts to exceed that of the clinically observed reaction at 48 hr and remains extensive even at 96 hr. The area of the increased RBC flux detected by the laser-Doppler technique corresponded generally to that of erythema for the first 48 hr, but thereafter became smaller than the clinically observable reaction. Cuff occlusion experiments showed that the phenomenon of reactive hyperaemia is abolished at 24 and 48 hr in conditions of maximal hyperaemia, but that this response is recovering by 96 hr. Vasomotion was significantly exaggerated between 48 hr and 96 hr. These studies indicate that there is maximal arteriolar vasodilatation during the first 2 days of the reaction with rapid blood flow in the congested capillaries of the dermal papillae, and that engorgement of deeper venous plexus of the dermis is the predominant vascular change in the resolving response at 72-96 hr.

Adult↗
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

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↗