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Biomedical subjects

D K Harrison

Publications and source records attributed to D K Harrison.

At least 19 recordsLinked to original sources
PubMed1997

Use of lightguide spectrophotometry to investigate the effect of postural changes on skin oxygenation in deep venous insufficiency.

BACKGROUND: Postural changes play an important role in the development of venous disease. The aim of this study was to investigate skin oxygenation in patients with deep venous insufficiency. METHODS: Haemoglobin oxygen saturation (SO2) was measured with macro- and micro-lightguide spectrophotometry in clinically normal skin at the gaiter area with the leg in the supine position, raised to 45 degrees and on standing. Similarly, transcutaneous oxygen tension (PtcO2) and laser Dopper flux (LDF) values were obtained. SO2 was also measured after heating the skin to 44 degrees C in the supine and standing positions. RESULTS: SO2 and PtcO2 decreased on leg raising (P < 0.05 and P < 0.01 respectively). SO2 fell on standing (P < 0.05) while PtcO2 rose (P < 0.05). On heating the skin, SO2 increased (P < 0.05) on standing. LDF fell on standing (P < 0.005) but increased on leg raising (P < 0.05). CONCLUSION: Lightguide spectrophotometry showed a profound decrease in skin oxygenation on standing and leg raising; PtcO2 measurements may miss the role of vasoconstriction with postural changes.

Adult↗
PubMed1996

What are the indications for a carotid duplex scan?

Carotid duplex scanning offers a quick and non-invasive method for detecting extracranial carotid arterial disease. However, the increasing awareness of the association of carotid disease and cerebrovascular symptoms, together with the recognition that carotid endarterectomy offers the possibility of prevention of a major stroke [1], means that requests for investigation are constantly increasing. The Dundee Vascular Laboratory undertakes the majority of carotid duplex scans in the Tayside region and we have found an increasing burden is being placed on a limited resource that is required for other vascular investigations. In 1994 we carried out 1389 carotid examinations of which 929 (66.9%) showed either no abnormality or no more than a 50% stenosis in one vessel. More importantly, of the 1052 new requests 832 (79.1%) fell into the same category. In order to ascertain if the number of new requests could be reduced a retrospective analysis of the referral indications for a carotid duplex scan in the last 5 years has been undertaken.

Adolescent↗
PubMed1995

Use of lightguide spectrophotometry to quantify skin oxygenation in a variable model of venous hypertension.

A variable model of venous hypertension was used to examine the immediate effect on skin oxygenation and blood flow. Measurements were carried out using laser Doppler flowmetry, transcutaneous oximetry and both macro- and micro-lightguide spectrophotometry to measure haemoglobin saturation (SO2). Assessments were performed on 20 normal subjects and in ten patients with deep venous insufficiency lying supine with a pressure cuff left uninflated (P0), then inflated to 40 mmHg (P40), 60 mmHg (P60) and 80 mmHg (P80). All measurements were performed at the gaiter area of the leg. In normal subjects median Doppler values fell significantly at P40 (P < 0.001) but further pressure increases had no more effect. Mean values of transcutaneous partial pressure of oxygen (PtcO2) fell steadily (P < 0.001), although the initial fall at P40 was small. Median SO2 fell with increasing occlusion pressure with both macro- and micro-lightguide spectrophotometry (P < 0.001), although the main reduction occurred predominantly at lower occlusion pressures. Higher levels of SO2 were obtained with local heating up to 44 degrees C, with a pattern similar to that of PtcO2. In patients, the same pattern of response to increased venous pressure occurred in areas of clinically normal skin. These data suggest that small increases in venous hypertension have an immediate and profound influence on skin blood flow and oxygen availability in normal skin.

Adult↗
PubMed1995

Symptoms, stenosis and carotid plaque morphology. Is plaque morphology relevant?

OBJECTIVES: To study the relationship between carotid plaque morphology and the degree of stenosis on Duplex ultrasonography and symptoms. DESIGN: Prospective open clinical study. METHODS: 2,590 patients with 5,180 carotid arteries were scanned, 4,560 were initially analysed in terms of symptoms but 54 were excluded, leaving a total of 4,258. RESULTS: Localising symptoms were present with respect to 1,342 vessels (29.4%). Two-thirds of symptomatic patients had normal carotid arteries. Tight stenosis (80-99%) was more likely to be associated with symptoms than low-grade (20-79%) stenosis (chi 2 = 28.0, p < 0.0001). Plaque type was identified in 1,558 bifurcations (36.6%). Heterogeneous type I & II plaques accounted for one third of plaques. There was a relationship between plaque morphology and degree of stenosis. At < 20% stenosis only 4.4% of plaques were heterogeneous whereas at 80-99% stenosis 84.5% of plaques were heterogeneous. Amaurosis fugax was the only symptom that had any association with a particular plaque morphology. Seventy-two percent of plaques associated with this symptom were heterogeneous in nature. CONCLUSIONS: Carotid plaque morphology and degree of internal carotid stenosis are mutually dependent factors and both reflect the severity of atherosclerotic disease. Plaque morphology does not add to the sensitivity of stenosis in predicting the presence of symptoms.

Blindness↗
PubMed1995

Amputation level assessment using lightguide spectrophotometry.

The aim of this experimental study was to investigate whether lightguide spectrophotometry in the visible wavelength range in skin could be used to predict stump healing viability in patients with critical lower limb ischaemia. Remission spectra recorded at two sites (medial and lateral) on the line of a proposed trans-tibial amputation (TTA) and at 10mm intervals along the leg were analysed to give haemoglobin oxygenation (SO2). Degree of tissue hypoxia (DTH) along the leg was defined as the percentage of values along the leg less than 10% SO2. DTH and mean SO2 values were compared with skin blood flow values ((I125) 4-Iodoantipyrine clearance technique) and clinical outcome of trans-tibial amputation, (TTA) or trans-femoral amputation (TFA), in 41 patients. SO2 histograms were also measured in 12 normal subjects for comparison. The results of the study allowed the establishment of criteria for the accurate prediction of flap healing potential. Successful TTAs all displayed a minimum mean SO2 at the medial and lateral measurement sites of 30%, together with a maximum degree of tissue hypoxia of 15% along the limb. The combination of these criteria gave a sensitivity and selectivity of 1.0 for prediction of a successful outcome of TTA.

Amputation, Surgical↗
PubMed1994

Transcutaneous hydrogen clearance--a new non-invasive technique for assessing blood flow in human skin.

A new technique for the non-invasive assessment of skin blood flow is described using a modified, commercially available transcutaneous oxygen electrode. Initially, experiments were carried out on normal volunteers at skin temperatures of 40 degrees C and 44 degrees C. Transcutaneous H2 (tcpH2) clearances were measured after the subject had breathed a mixture of 2% H2 in air until a saturation value in the skin had been reached. tcpH2 clearance results were compared with laser Doppler flux values measured simultaneously on adjacent sites and at the same temperatures under control and reactive hyperaemic conditions. Good reproducibility for the tcpH2 technique and significant correlation (p < 0.002) between it and laser Doppler flux values at the same temperatures was demonstrated. In further experiments, (I125) 4-iodoantipyrine clearances (IAP) were carried out immediately prior to and at the same sites as tcpH2 clearances in critically ischaemic lower limbs. The correlation between the methods and the differences between tcpH2 values observed in normal and critically ischaemic skin were highly significant (p < 0.002).

Adult↗
PubMed1994

Comparison of macro- and micro-lightguide spectrophotometric measurements of microvascular haemoglobin oxygenation in the tuberculin reaction in normal human skin.

The changes in haemoglobin oxygenation (SO2) occurring in the tuberculin reaction in human skin were measured using macro- and micro-lightguide spectrophotometry and the results compared. A significant difference was found between the measurements from the respective instruments, demonstrating that the micro-lightguide technique measures only in the most superficial capillaries. Laser Doppler flux (LDF) and transcutaneous oxygen (tcpO2) measurements were also obtained concurrently. At the height of the reaction, heating did not significantly change SO2 or LDF, showing that the vessels in the skin were maximally vasodilated. Although SO2 was increased in the reaction, tcpO2 decreased. This suggests that the infiltrating cells may present a diffusion barrier to oxygen between the capillaries and the tissue cells. This study has shown that micro-lightguide spectrophotometry gives a local picture of intracapillary oxygen supply, which is useful in elucidating the pathophysiological changes occurring during chronic inflammation.

Adolescent↗
PubMed1994

Effect of hyperoxia at 1 and 2 ATA on hypoxia and hypercapnia in human skin during experimental inflammation.

Transcutaneous PO2 and PCO2 measurements and estimates of skin respiration were monitored at different levels of inspired PO2 in 20 healthy adults during the first 4 days of the tuberculin reaction, a convenient model of acute inflammation. Hyperoxia at 1 and 2 ATA significantly increased transcutaneous PO2 levels in undisturbed and in inflamed skin but did not fully correct the relative hypoxia at the site of inflammation. Hypercapnia was reduced with O2 breathing at 2 ATA. The apparent rate of O2 consumption at the reaction site was raised during hyperoxia, most prominently at 2 ATA. The most intense reactions showed a central relative slowing of laser-Doppler blood flow indicative of microcirculatory impairment. The extent of the relative hypoxia and hypercapnia was greatest in these strongest reactions. The density of lymphocytes and monocytes in biopsies of 48-h reactions was loosely related to the corresponding transcutaneous PO2 measurements. The present study provides evidence that diffusion barriers, in addition to increased local respiration, can contribute to the apparent hypoxia and hypercapnia of this inflammatory model.

Adult↗