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Biomedical subjects

M Halliwell

Publications and source records attributed to M Halliwell.

At least 37 records · Page 2Linked to original sources
PubMed1992

Estimation of total hepatic blood flow by duplex ultrasound.

The volume flow rate of blood in the portal vein and the hepatic artery was measured using a duplex ultrasound system. Two sections of the hepatic artery were studied; the common hepatic artery where measurements were made just after the bifurcation of the coeliac axis to splenic and hepatic arteries and the hepatic artery itself, where measurements were made just proximal to the porta hepatis in a straight stretch of artery overlying the portal vein. Total hepatic blood flow was taken as the sum of hepatic artery and portal vein flows. A group of 10 normal healthy volunteers in the fasting state was studied. The mean (SD) volume blood flow in the vessels was measured to be: hepatic artery 3.5 (45%) ml/min/kg, common hepatic artery 6.9 (30%) ml/min+/kg, portal vein 13.5 (21%) ml/min/kg, total hepatic flow 17.0 (16%) ml/min/kg.

Blood Flow Velocity↗
PubMed1992

The envelope that tissue imposes on achievable ultrasonic imaging.

Ultrasonic images are imperfect because practical imaging systems have limited spatial, contrast, and temporal resolutions. The envelope within which an ultrasonic imaging system operates is imposed by the physical and biological properties of the imaged tissue. The relevant properties are speed, attenuation, inhomogeneity, nonlinearity, scattering, motion, and the induction of biological damage. The system designer begins by choosing the overall dimensions of the tissue structures to be imaged and the imaging rate. Then, optimization of system design allows the imaging performance to coincide with the envelope imposed by the characteristics of the tissue.

Humans↗
PubMed1991

Ultimate limits in ultrasonic imaging resolution.

According to elementary theory, the resolution of an ultrasonic imaging system increases with the ultrasonic frequency. However, frequency is limited by frequency-dependent attenuation. For imaging at any required depth, resolution improvement beyond the limit imposed by ultrasonic frequency can be obtained by increasing the ultrasonic intensity. This is itself, however, dependent on safety considerations and the effects of nonlinearity. In homogeneous media, image resolution increases with decreasing f-number. Particularly at low f-numbers, however, tissue inhomogeneity leads to a deterioration in image quality. Inhomogeneity may also be considered in terms of phase aberration. It has been found that for a given aperture, image degradation due to phase aberration is worse at higher frequencies. Schemes have been proposed for correction of this problem, but so far model systems do not lend themselves to clinical application. Deconvolution is unsatisfactory, speed correction is impracticable and synthetic aperture scanning and holography are virtually useless in biological tissues. Ultrasound-computed tomography has had only limited success. Speckle reduction can improve target detectability, but at the expense of resolution. Time-frequency control provides a useful partial solution to the problem of resolution reduction resulting from attenuation. It is clear that improved resolution would result in significant clinical benefits. An optimisation system for aperture size and ultrasonic frequency is proposed with signal averaging for resolution enhancement of a defined object area. This would have a compact ultrasonic beam and would allow frame rate to be traded for resolution, by means of signal averaging.

Humans↗
PubMed1991

Fasting and post-prandial splanchnic blood flow is reduced by a somatostatin analogue (octreotide) in man.

1. The effects of the subcutaneous administration of a long-acting somatostatin analogue (octreotide) or of placebo on the splanchnic blood flow response to a mixed solid meal has been examined in eight normal subjects by using a transcutaneous Doppler ultrasound technique. Each subject was studied on two occasions more than 1 week apart. 2. On the control day, feeding had a pronounced effect on both superior mesenteric artery and portal venous blood flows, causing a peak rise of 82% in superior mesenteric artery blood flow at 15 min and of 75% in portal venous blood flow at 30 min post-prandially (P less than 0.001). Blood flows remained elevated 2 h after the meal. Pulse and blood pressure showed no significant changes from baseline. 3. Octreotide reduced fasting superior mesenteric artery blood flow by 59% (P less than 0.05) and portal venous blood flow by 49% (P less than 0.01) and blunted the normal post-prandial rise. Pulse and blood pressure did not change in response to either the injection or the ingestion of the meal. 4. Octreotide suppressed the release of insulin, glucagon and pancreatic polypeptide in response to feeding and resulted in post-prandial hyperglycaemia. 5. The mechanism of action of octreotide on splanchnic blood flow is uncertain. It may be mediated via a direct vascular effect or it may act via suppression of vasoactive intestinal hormones.

Adult↗
PubMed1991

Splanchnic haemodynamic changes during acute hypoglycaemia in man.

1. Splanchnic haemodynamic changes were studied in seven healthy subjects during hypoglycaemia induced by the intravenous infusion of insulin. Superior mesenteric artery blood flow and cardiac output were examined noninvasively by a Doppler ultrasound technique. 2. Blood glucose concentration fell from 4.5 (0.14) mmol/l basally to 1.5 (0.09) mmol/l [mean (SEM), P less than 0.003] at the hypoglycaemic reaction ('R') and recovered to baseline by 'R' + 60 min. There was an associated rise in plasma glucagon, adrenaline and noradrenaline levels. 3. Superior mesenteric artery blood flow rose at 'R' from a basal value of 532 (38) ml/min to a peak of 803 (73) ml/min at 'R' + 10 min [mean (SEM), P less than 0.005] and remained significantly elevated until 'R' + 40 min. Resistance in this vessel fell by 33% at 'R' + 10 min (P less than 0.005) and remained significantly low until 'R' + 40 min. 4. Cardiac output rose by 33% at 'R' (P less than 0.004) and returned to normal by 'R' + 20 min. This was associated with a 24% rise in pulse rate (P less than 0.03), but no change in stroke volume or mean arterial pressure. Total peripheral resistance fell by 21% at 'R' (P less than 0.005) and had returned to normal by 'R' + 20 min. 5. The sustained rise in splanchnic blood flow during hypoglycaemic recovery may be of homoeostatic importance by providing metabolic fuel to the liver for gluconeogenesis.

Adult↗
PubMed1991

Measurement of lithotripsy pulses through biological media.

Lithotripsy is now the method of choice for the treatment of renal calculi. The mechanism of destruction is not clearly understood, and detailed knowledge of the shock-wave characteristics at the calculus would aid understanding of the phenomenon. Current methods of measuring the pressure pulse by observing it through a water path are not well characterized, and the results may not represent the actual pressure fluctuations produced in vivo. In order to determine the actual pressure pulse experienced at the site of the calculus, measurements have been made through a variety of biological media. The results show that there are considerable differences between measurements taken through a water path and through biological media. This paper describes the pressure fluctuations in the time domain. The implications of the results for lithotripsy are discussed.

Animals↗
PubMed1989

Measurement of normal portal venous blood flow by Doppler ultrasound.

The volume flow rate of blood in the portal vein was measured using a duplex ultrasound system. The many errors inherent in the duplex method were assessed with particular reference to the portal vein and appropriate correction factors were obtained by in vitro calibration. The effect of posture on flow was investigated by examining 45 healthy volunteers in three different positions; standing, supine and tilted head down at 20 degrees from the horizontal. The mean volume blood flow in the supine position was 864 (188)ml/min (mean 1SD). When standing, the mean volume blood flow was significantly reduced by 26% to 662 (169)ml/min. There was, however, no significant difference between flow when supine and when tilted head down at 20 degrees from the horizontal.

Adult↗
PubMed1989

New scans from old: digital reformatting of ultrasound images.

Two-dimensional images obtained using ultrasound have been digitized from videotape recordings and stored within a maximum of 240 digital memory planes to form a three-dimensional data set using a commercially available image processing unit. This data set has been manipulated to produce images in planes perpendicular to the original scan set. The reformatted images represent not only the scans that could have been obtained by rotating the scan head but also demonstrate planes that are not accessible by conventional scanning. The system has been evaluated with a tissue-equivalent phantom to determine the geometric accuracy of the reformatting process. Clinical material has also been used to evaluate the practical value of such a technique and to highlight difficulties that may be encountered in its routine use.

Abdomen↗
PubMed1985

The self concept of adolescents with spina bifida.

A study of the children's self concepts was conducted as part of the twelve year follow-up phase of the Greater London Council's Spina Bifida Survey. On the three measures used, there were few significant differences between the spina bifida children and controls, nor between the spina bifida children divided according to such variables as disability level or school type. It was hypothesised that, at twelve years, the children had not yet developed sufficient self-awareness or ability to appreciate the wider implications of their disability, therefore a further sample of spina bifida teenagers was tested. The results from both spina bifida groups showed few significant differences, suggesting that the self concepts of young people with spina bifida in early and later adolescence are neither markedly different from those of their peers, nor associated with degree of disability level or type of school attended. Early hospitalisation was negatively correlated with self concept at twelve years (equivalent data were not available for the teenagers) and this finding is discussed.

Adolescent↗
PubMed1984

The relationship of disability and school type to everyday life.

The relationships between disability and school type, and aspects of the everyday lives of 11-year-old children in the GLC Spina Bifida Survey, were explored. The more disabled children were found to be less likely to go out on their own or with friends, although not less likely to go out with sibs or adults. They were equally likely to have friends visiting them at home, but less likely to have friends living in the locality, and to go out to visit them. Special school children were more often described as lonely, and of children with visible disabilities those in special schools were more often teased outside school than were those in ordinary schools. Personality ratings by teachers showed little difference between the spina bifida children and other groups of non-handicapped children, but ratings by mothers suggest that the spina bifida children were more likely to alternate between childish and adolescent behaviours.

Activities of Daily Living↗
PubMed1983

The effect of disability on family life.

In the GLC Spina Bifida Survey families were interviewed at 11 years old and the effects of a child with spina bifida on the sibs, father and mother were explored. Health and behaviour of the sibs were reported as at least as good as that of sibs of normal children although mothers of disabled children were more likely to feel that the sibs had suffered. Fathers appeared to have been unrestricted in occupational choice; over the last 9 years 40% had moved upward in social class, twice as many as those who had moved downward. Parents of severely disabled children were significantly more restricted in some social activities than were those of the lightly disabled, and significantly more mothers of SB than of controls reported feeling run-down and depressed. No significant relationship could be found between measures of either health or stress in the parents and any measure of the child's disability level, dependence or amount of hospitalisation, nor with measures of social restriction. There is nevertheless a continuing need for help and support for families of disabled children, for them to make use of as they wish.

Child↗
PubMed1982

Ultrasonic Doppler studies of the breast.

The growth of a malignant tumour depends on vascularisation. The ultrasonic Doppler method can detect the blood flow associated with malignant breast tumours, the signals differing qualitatively from those due to benign lesions. Several descriptors of the Doppler signals were tested; benign and malignant lesions are best separated by the difference between the maximum systolic frequencies from suspect and contralateral sites. Corresponding main arterial sites are reliably coincident in normal breast pairs. Consideration of the powers and frequency spectra of Doppler signals leads to the rejection of models of tumour vascularisation giving Doppler signals based on capillary perfusion and on a single feed artery. The data are compatible with a multiple feed artery model, and this is supported by a contrast angiogram. Doppler ultrasound may be useful as a preliminary screening method, in the management of patients with radiologically dense breasts or diffuse dysplasia, and for monitoring unexcised tumours undergoing hormone therapy.

Adenocarcinoma↗
PubMed1979

Antipyrine clearance per unit volume liver: an assessment of hepatic function in chronic liver disease.

Liver size has been estimated clinically and by a non-invasive ultrasound technique in 16 normal subjects, 16 patients with cirrhosis, 10 patients with chronic biliary obstruction, and three patients with primary hepatoma. Antipyrine disposition was also measured in each subject. Hepatomegaly was not clinically detectable until there was approximately a 20% increase in liver size. Additional increases in size correlated significantly with clinical estimates of hepatomegaly. Antipyrine clearance had a three-fold range in normal subjects. Its mean value was significantly reduced in each subgroup of patients with liver disease. However, 48% of patients with liver disease had values within the normal range. In normal subjects there was a significant correlation between antipyrine clearance and liver volume. Thus, intersubject variation in clearance normalised for liver volume was less than clearance alone. Antipyrine clearance normalised for liver volume in patients with liver disease was significantly lower than in normal subjects and there was no overlap with normal subjects. In conclusion, assessment of drug metabolising efficiency per unit volume of liver increased the discrimination in differentiating subjects with normal from abnormal livers.

Aged↗