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Biomedical subjects

S B Sherriff

Publications and source records attributed to S B Sherriff.

17 recordsLinked to original sources
PubMed1999

Time-averaged mean velocity for volumetric blood flow measurements: an in vitro model validation study using physiological femoral artery flow waveforms.

This study assesses the accuracy of the volume flow measurement of the ATL HDI 3000 duplex ultrasound scanner using a model of the femoral arterial circulation. The beam profile of the transducer was measured, and used to identify regions of the beam where there may be poor insonation characteristics. The flow measurement accuracy was not found to be influenced by the vessel depth between 1.0 cm and 8.0 cm in a 0.7 cm diameter vessel. Overall accuracy was 3%+/-9%. Vessels in excess of 0.9 cm produced larger errors. In the model system, pulse rates between 60 bpm and 120 bpm had no significant effect on the measurement accuracy (p > 0.01). The results of this study suggest that accurate measurements of femoral arterial blood flow are possible. Further work will be required to assess the accuracy of the technique in vivo.

Blood Flow Velocity↗
PubMed1999

Latex vessels with customized compliance for use in arterial flow models.

The physical characteristics of the arterial wall exert a major influence over blood flow patterns and the pulse wave velocity is strongly affected by the elasticity of the vessel. We have developed a technique for manufacturing latex tubing which has physical characteristics similar to those of human arteries. Tubes were produced by painting a plastic rod of diameter 7 x 10(-3) m (the internal diameter of the superficial femoral artery) with liquid latex. The number of coats applied controlled the thickness, and hence the elasticity of the resulting tube. Values of compliance and pulse wave velocity were similar to those observed in vivo. The tubing was tested in a model of the femoral arterial circulation and the typical triphasic arterial now was seen. The mean flow in the vessels was also analysed, and found to be higher for the more elastic vessels, supporting existing mathematical theories and qualitative physiological data. These vessels provide a reliable method of producing physiologically accurate test segments for use in a range of arterial flow models.

Artificial Organs↗
PubMed1998

Impaired fetal growth and atherosclerosis of carotid and peripheral arteries.

BACKGROUND: Although epidemiological studies suggest that people with low birthweight are at higher risk of coronary heart disease and stroke in adult life than those of higher birthweight, the mechanisms underlying this relation are unclear. We investigated whether impaired fetal growth leads to an increased risk of atherosclerosis by assessment of the carotid and lower-limb arteries in a group of people aged around 70 years for whom birthweight data were available. METHODS: 2232 singleton babies were born to married mothers at a maternity hospital in Sheffield, UK, between 1922 and 1926, and had complete birth records. We traced 829 survivors and invited 395 who still lived in Sheffield to take part in this study. 322 agreed; they were interviewed at home and 181 underwent duplex ultrasonographic examination of the extracranial parts of the carotid arteries. Atherosclerosis in the arteries of the lower limb was assessed in 186 people by the ankle-brachial-pressure index (ABPI). FINDINGS: The prevalence and severity of carotid atherosclerosis was greatest in those with the lowest recorded birthweight. The risk of carotid stenosis was greater for people who had weighed 6.5 lb or less at birth than for those who weighed over 7.5 lb (odds ratio 5.3 [95% CI 2.0-14.0]), after adjustment for cardiovascular risk factors and gestational age at birth. The odds ratio for atherosclerotic disease in the lower limbs (low ABPI) was highest in people with the lowest recorded birthweight, but this relation was not significant (odds ratio 2.3 [1.0-5.6]). INTERPRETATION: Increased atherogenesis may be one mechanism mediating the observed epidemiological link between impaired fetal growth and cardiovascular disease. Adaptations made by the fetus in response to influences that retard its growth may have long-term consequences for the structure and metabolism of the vascular system.

Aged↗
PubMed1991

The effect of dobutamine on middle cerebral artery blood velocity in volunteers: a preliminary study.

Five volunteers given dobutamine up to 4 micrograms/kg/min had significant increases in mean arterial blood pressure, systolic blood pressure, and stroke volume (P less than 0.05). Heart rate did not increase significantly. Pulsatility index, an index of middle cerebral artery maximum blood velocity waveform shape increased significantly in the dobutamine group (P less than 0.05). Time-averaged mean velocity did increase during the dobutamine infusion but the change was not statistically significant. Dobutamine significantly alters the blood velocity profile of the middle cerebral artery in volunteers even in low doses of 4 micrograms/kg/min. Transcranial Doppler may be a useful technique to monitor changes in cerebral artery blood velocity dynamics induced by dobutamine. These measurements can be performed easily and repeatedly at the bedside.

Adult↗
PubMed1989

A simple quantitative screening test for the detection of extracranial carotid artery disease.

A simple screening test, using continuous wave Doppler ultrasound, for the detection of all grades of extracranial carotid artery disease has been described. The test is composed of two parts: (1) the determination of the direction of flow at the orbit and (2) on-line principal component factor analysis of the maximum frequency envelope of the Doppler shifted signal obtained from the common carotid artery. A total of 154 vessel segments have been investigated; 69 normal, 41 with a stenosis of 10-49%, 32 with a stenosis of 50-99% and 12 occlusions. Of these, 70 vessel segments were assessed prospectively and they formed the data base from which the principal components and the classification factor were calculated. The remaining 84 vessel segments were analysed prospectively on-line. The combined results gave an overall sensitivity to the detection of disease of 90% and a specificity of 77%. It has been shown that although classification of Doppler waveforms by principal component analysis is a fairly sophisticated technique it is possible, by careful design of the algorithms, to design a near real-time on-line analysis system for derived waveforms such as the maximum frequency envelope.

Algorithms↗
PubMed1987

Real-time analysis of Doppler waveforms.

The usefulness of objective analysis of Doppler waveforms is now well established but to date such measures have generally not been available in real-time. This Paper describes a real-time data analysis and collection system in use with a duplex scanner which is capable of producing objective measures of waveform shape during the investigation. It is shown as an example that this information can be used to identify, with high accuracy, babies likely to be classified at birth as distressed as early as the 34th week of pregnancy.

Female↗
PubMed1987

Comparison of laser Doppler and Doppler ultrasound in lower limb vascular diagnosis.

This study represents a preliminary investigation into the use of laser Doppler flowmetry in lower limb vascular diagnosis. The method is compared with the accepted method of continuous wave Doppler ultrasound. Fifty-six patients with symptoms of lower limb vascular disease were investigated consecutively and independently using both techniques. In approximately two-thirds of patients the two methods showed broad agreement in their classification of disease severity (correlation coefficient = 0.63, P less than 0.001, n = 41). However, about 30% of those studied had impaired microvascular responses on laser Doppler evaluation with no detectable major vessel disease on continuous wave ultrasound investigation. The results indicate that more information is obtained about a subject's vascular status when results from both methods are combined. Thus laser Doppler flowmetry may be useful adjunct to Doppler ultrasound and segmental pressure measurements in the vascular laboratory.

Adult↗
PubMed1986

Carotid artery blood flow: single factor classification of Doppler waveforms.

The usefulness of principal components factor analysis as a way of classifying Doppler waveforms from the carotid artery has been established. The waveform is first reduced to a small set of coefficients which capture, via their associated principal components, the essential shape of the waveform. The vector of these coefficients can be used to classify the waveform by finding the position of this vector in a classification space relative to one or more classifying surfaces. This short communication will show how these two steps may be combined to produce a single factor for classification.

Carotid Arteries↗
PubMed1983

Reticuloendothelial function in coeliac disease and ulcerative colitis.

Patients with ulcerative colitis and coeliac disease who had been shown by impaired clearance of heat damaged red cells to have diminished splenic phagocytosis, were examined for evidence of more generalised reticuloendothelial malfunction by measuring their circulatory clearance of micro-aggregated albumin. Although in animals micro-aggregated albumin is largely removed by Kupffer cells, we found impaired clearance in otherwise normal subjects who had previously had surgical splenectomy. In patients with hyposplenism because of bowel disease there was no additional impairment of micro-aggregated albumin clearance, indicating that their hyposplenism is an isolated phenomenon and not part of a generalised reticuloendothelial atrophy. Patients with coeliac disease and normal splenic function had increased reticuloendothelial catabolic activity; this was not present in patients with coeliac disease and abnormal splenic function.

Adolescent↗
PubMed1983

An objective feature extraction technique applied to the Doppler waveforms from the groin: a prospective study.

A group of 80 patients presenting with lower limb ischaemia were classified according to their arteriographic findings. The maximum frequency envelope from the Doppler waveforms obtained from the common femoral artery were retrospectively analysed using a mathematical feature extraction technique, principal component analysis (PCA). Two of the three coefficients uniquely describing each waveform were plotted and classified according to their arteriographic groupings. The best separating planes were then defined. Twenty-eight new patients were subsequently prospectively assessed using the principal components and separating planes defined in the previous study. The results were compared with the arteriographic findings and showed that PCA represents a significant improvement in diagnostic accuracy when compared with other techniques.

Aorta↗
PubMed1981

A prospective study of the accuracy of Doppler ultrasound in detecting carotid artery disease.

Results are presented from a two year prospective study using a Doppler ultrasound technique for the detection of carotid disease. The patients studied presented with transient cerebral ischaemic attacks or small strokes in the carotid territory. No other form of patient selection was used. Results were compared with those from carotid and arch aortography. 86% of normal vessels and 78% of diseases vessels were correctly classified. It is concluded that this technique offers a safe and accurate screening procedure for the management of patients presenting with transient cerebral ischaemia or small strokes.

Arteriosclerosis↗
PubMed1981

Further experience of hyposplenism in inflammatory bowel disease.

We have reported previously the association between hyposplenism and inflammatory bowel disease. Our study has now been extended to a total of 65 patients with ulcerative colitis and 42 with Crohn's disease so that the incidence of hyposplenism could be more accurately determined. Hyposplenism rarely complicated distal ulcerative colitis, but was found in 15 of 37 patients with total colonic disease. Hyposplenism occurred in 11 out of 31 patients with Crohn's disease of the colon, but in none of 11 individuals with isolated ileal disease. In order to determine whether hyposplenism has any prognostic implications, the peri-operative course of 12 hyposplenic individuals who underwent colectomy was compared with that of 12 controls who required surgery and who had normal splenic function. Four of the hyposplenic subjects became severely shocked after operation and developed disseminated intravascular coagulation. In contrast, the post-operative course in the control patients was uneventful.

Adolescent↗
PubMed1977

Clinical study of liver blood flow in man measured by 133Xe clearance after portal vein injection.

During the course of a clinical trial to assess the value of adjuvant liver perfusion of 5-fluorouracil after surgery for colorectal cancer, liver blood flow was measured in 14 patients. Access to the portal circulation was achieved by dilatation and cannulation of the obliterated umbilical vein. The clearance from the liver of a bolus of 133Xe was monitored using a gamma-ray camera so that blood flow from different areas of the liver could be calculated. The clearance curve of 133Xe was a double exponential of which the initial fast component accounted for a consistently high proportion of the total clearance. The perfusion studies have shown wide differences in blood flow to the various areas of the liver in the same patient, in addition to a wide variation in perfusion rate between the 14 patients. This technique of quantitative estimations of liver blood flow to different areas of the liver may have importance in planning operative procedures and understanding the haemodynamic mechanisms involved in liver disease.

Humans↗