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Biomedical subjects

M Halliwell

Publications and source records attributed to M Halliwell.

At least 19 recordsLinked to original sources
PubMed2000

Intervertebral disc structure: observation by a novel use of ultrasound imaging.

The internal structure of intervertebral discs is clinically important in the management of back pain. No current routine imaging modality is able to image disc structure satisfactorily. The aim of this work was to investigate and validate ultrasound imaging so that it might be applied to assessment of structural integrity and degree of degeneration. The optimum imaging technique was determined using a 3.5 MHz probe in one female subject. The applicability of this technique to investigate disc structure in the entire thoracolumbar spine was further investigated in 13 subjects. The optimum disc imaging technique was found to be a posterolateral approach, 1 to 2 cm lateral of the dorsal midline, that revealed structure within the disc not apparent using other approaches. It was demonstrated that posterolateral imaging introduces a smaller reproducibility error in measurements of linear dimensions close to the disc. It is possible to observe internal structure within the disc between T11 and L3 in at least 54% of individuals.

Adolescent↗
PubMed1999

Development of a system to record cardiac output continuously in the newborn.

Intermittent recordings of Doppler flow velocity and cardiac output are of value during intensive care of the sick newborn infant but result in repeated disturbance of the child. We describe a new device for making continuous precordial recordings of Doppler flow velocity from the pulmonary artery in healthy resting newborn infants. Optimal probe siting was evaluated in six babies, and signals were found to be best when the pulmonary artery was insonated from the mid left parasternum. Continuous recordings were made in 13 other babies. Pulmonary artery velocities and, by calculation, cardiac output were measured continuously over periods ranging from 24 to 60 min. Median right ventricular output ranged widely from 148 to 246 mL x kg(-1) x min(-1). In contrast, for individual babies, the values were remarkably stable: the interquartile ranges varied from 13.2 to 29.9 mL x kg(-1) x min(-1). The simultaneous display of signal power allowed independent assessment of artifactual changes in cardiac output. This technique is feasible in healthy term infants and now requires evaluation in the intensive care setting where it may provide useful information concerning trends and short-term variability in right ventricular output.

Cardiac Output↗
PubMed1999

Physiological control of splanchnic blood flow by adrenaline: studies during acute hypoglycaemia in man.

Superior mesenteric artery blood flow (SMABF) increases significantly during and after the hypoglycaemia reaction in healthy humans. To investigate the mechanisms controlling this phenomenon, SMABF and plasma catecholamines were measured in healthy human volunteers. In 10 controls, hypoglycaemia was induced by insulin infusion (2.5 m-units.min-1.kg-1). In six subjects, beta-blockade by propranolol infusion (0.7 microgram.min-1.kg-1) preceded insulin infusion and was continued throughout the study. Following the hypoglycaemia reaction, the glucose nadir was similar in both groups. In controls, increases in SMABF [42.4+/-6.1% (mean+/-S.E.M.); P<0. 001], cardiac output (34.3+/-2.3%; P<0.001) and pulse rate (from 63. 9+/-2.7 to 82.5+/-3.1 beats/min; P<0.001) occurred. Superior mesenteric artery resistance fell by 32.4+/-3.3% (P<0.001). Under beta-blockade, decreases in SMABF (34.8+/-2.9%; P<0.001) and pulse rate (from 59.5+/-0.2 to 51.8+/-2.2 beats/min; P<0.001) occurred. Superior mesenteric artery resistance increased (peak +30.8+/-12.3%; not significant). Subjects showed greater increases in adrenaline (P<0.006) and noradrenaline (P<0.022) concentrations than controls. Mesenteric hyperaemia associated with hypoglycaemia in man appears to be mediated by a beta-adrenergic mechanism that is activated by increased circulating levels of adrenaline.

Acute Disease↗
PubMed1999

Increased splanchnic blood flow after hypoglycaemia in diabetic and normal man: evidence against glucagon as a mediator.

Superior mesenteric artery blood flow increases significantly after hypoglycaemia in healthy humans. Glucagon has vasoactive properties but its role in hypoglycaemic hyperaemia is unclear. To assess this role, we studied the superior mesenteric artery blood flow response to hypoglycaemia of patients with uncomplicated Type 1 (insulin-dependent) diabetes mellitus of at least 10 years duration; a group known to have defective glucagon response to hypoglycaemia. Hypoglycaemia was induced using an intravenous infusion of soluble human insulin (2.5 m-units.min-1.kg-1) discontinued at a plasma glucose of 2.5 mmol/l. Superior mesenteric artery blood flow was measured using transcutaneous duplex Doppler ultrasound. Plasma samples were assayed for glucose, insulin, glucagon, catecholamines, growth hormone and cortisol. Plasma glucose concentration fell to a nadir of 1.8 (0.3) mmol/l in patients and 1.4 (0.1) mmol/l in controls. Plasma glucagon concentration was unchanged in patients from a baseline level of 111.7 (13.1) ng/l but rose in controls from 105 (8.5) to a peak of 239 (3.1) ng/l (P<0.001). Superior mesenteric artery blood flow increased in both groups: from 385 (29) to 921 (100) ml/min (140% increase; P<0.05) in patients and from 517 (50) to 790 (67) (53% increase; P<0.001) in controls. This study shows that patients with Type 1 diabetes have a normal splanchnic vascular hyperaemic response to hypoglycaemia despite defective glucagon counter-regulation. These results support our previous work suggesting that glucagon is not a major mediator of this response; it seems likely that circulating adrenaline is the major regulatory mechanism.

Adult↗
PubMed1998

A comparison of digital retinal images and 35 mm colour transparencies in detecting and grading diabetic retinopathy.

We compared digital retinal images and 35 mm colour transparencies taken with the Canon CR5 retinal camera for the detection and grading of diabetic retinopathy in a clinical setting, in a randomized, blinded study of diabetic patients with a spectrum of severity of diabetic retinopathy. Forty patients were photographed, giving a total of 75 eyes including non-diabetic eyes as controls. Images were graded according to the validated European guidelines. There was exact agreement between grades obtained from both the 2 field 45 degrees 35 mm colour transparencies and digital images in 93.3% (70/75) of eyes, with Cohen's Kappa statistic for the comparison being 0.92. Overall, when grading from the digital images 5.3% (4/75) eyes were undergraded with three cases of sight threatening diabetic retinopathy (STDR) graded as non-sight threatening (NSTDR) (3/48, 6.3%). One eye was overgraded (1/75, 1.3%). Two of the three cases of STDR undergraded as NSTDR had small numbers of intra-retinal microvascular abnormalities (IRMA) discernible on the colour transparencies but which were not visible from the digital image. The third had multiple small cotton wool spots graded as laser photocoagulation scars from the digital images. In conclusion there is good to excellent agreement between retinopathy grades using the Canon CR5 digital retinal imaging system compared to 35 mm colour transparencies.

Diabetic Retinopathy↗
PubMed1997

Thyrotropin receptor transcripts in human adipose tissue.

Thyroid associated ophthalmopathy (TAO) is generally considered to have an autoimmune pathogenesis but the target antigen has yet to be identified. It is most frequently associated with Graves' disease and there is some logic in assuming that the same antigen, the thyrotropin receptor (TSHR), is the common link. Previous studies, mostly PCR based, aimed at investigating TSHR transcripts in the orbit, have yielded conflicting results, although there is circumstantial evidence for their presence in orbital fat. In this study, we have examined adult human adipose and muscle tissues from various locations, initially by PCR and subsequently by northern blot. We obtained the expected 610bp product in normal intestinal and orbital fat but not skeletal muscle, following two rounds of PCR amplification but only when reverse transcription used a TSHR specific primer. In northern blots, despite loading all of the RNA obtained from total normal orbital fat contents, TSHR transcripts were at the limit of detection and similarly for large samples of intestinal fat. The exception was RNA obtained from TAO orbital fat, in which TSHR transcripts of 4.6 and 1.7kb were clearly visible, as in the thyroid. We conclude that normal adult adipose tissues contain low levels of TSHR transcripts. In TAO, TSHR transcripts are elevated probably due to an increased number of cells, in particular of preadipocytes in orbital adipose tissue.

Abdomen↗
PubMed1994

Ultrasound quantitation of respiratory organ motion in the upper abdomen.

Organ motion can cause artefacts in abdominal imaging particularly with magnetic resonance imaging (MRI), and may often limit the diagnostic quality of an image. If spatial resolution and image quality are to improve in MRI and other imaging techniques, a more detailed understanding of organ motion is required. Despite the importance of organ motion little quantitative information is available to date. This study was the continuation of work instigated to investigate and quantify respiratory movements of upper abdominal organs for a group of healthy volunteers in order to provide the design criteria for a motion test object for use in MRI. A previous phase of the project allowed construction of a test object but refinements were needed to represent respiratory motion more closely as a consequence of the data presented in this paper. Improvements in the scanning technique and the recording procedure have revealed that, contrary to our initial findings, motion of the diaphragm and liver is predominantly in the superior-inferior (SI) direction with an average displacement (+/- SD) (quiet respiration) of 12 +/- 7 mm (range 7-28 mm) and 10 +/- 8 mm (range 5-17 mm), respectively. For some volunteers, motion of the kidneys can be complex, especially during deep inspiration. New data have been provided by this phase of the motion study on the displacement, velocity and acceleration of abdominal organs as a function of time. These data show that MRI motion artefact reduction techniques which assume that either organ displacement, velocity or acceleration are constant are only applicable during certain phases of the respiratory cycle.

Diaphragm↗
PubMed1993

Evidence against a putative role for glucagon as a physiological splanchnic vasodilator in man.

1. Previous studies have suggested that glucagon in supraphysiological doses may mediate postprandial and hypoglycaemia-induced splanchnic vasodilatation in man and experimental animals. There are no reported studies investigating the role of glucagon in doses producing circulating concentrations within the physiological range. 2. Two separate studies were performed. In study 1, superior mesenteric artery blood flow was measured by Doppler ultrasound in six normal subjects during either saline or glucagon infusion at 1, 3 and 6 ng min-1kg-1, which resulted in circulating glucagon levels within the physiological range. Mean superior mesenteric artery blood flow fell during the 3 and 6 ng min-1kg-1 glucagon infusions (3 ng min-1kg-1: -31.8%, range -20 to -56% of baseline; 6 ng min-1kg-1: -20.7%, range -8 to -53% of baseline; P < 0.05). 3. In study 2, superior mesenteric artery blood flow was measured during hypoglycaemia induced by an insulin infusion in 12 normal subjects. In six of these subjects the effect of suppression of glucagon release during hypoglycaemia was assessed by pretreatment with the somatostatin analogue octreotide (0.8 microgram/kg subcutaneously) given 30 min before the insulin infusion. 4. The nadir in blood glucose concentration at the hypoglycaemic reaction was similar in both groups and glucose recovery was complete by 60 min after the hypoglycaemic reaction. Plasma catecholamine concentrations rose in both groups after the hypoglycaemic reaction. 5. Superior mesenteric artery blood flow rose at the hypoglycaemic reaction in both groups despite suppression of glucagon release with octreotide.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Splanchnic blood flow in man: evidence for mediation via a beta-adrenergic mechanism.

1. Superior mesenteric artery blood flow was examined by Doppler ultrasound in six male subjects aged 19-23 years during the infusion of saline (control), 10 and 40 ng of adrenaline min-1kg-1 for 30 min, or propranolol and 10 ng of adrenaline min-1kg-1 for 30 min, on four separate occasions. 2. Adrenaline infusion resulted in significant peak mean (SEM) rises in circulating adrenaline concentrations during the infusion period only [control, 0.20 (0.05) nmol/l; 10 ng of adrenaline min-1kg-1, 1.37 (0.29) nmol/l; 40 ng of adrenaline min-1kg-1, 3.73 (0.40) nmol/l; 10 ng of adrenaline min-1kg-1 and propranolol, 1.48 (0.16) nmol/l, P < 0.001 versus control]. These values are within the physiological range. 3. Superior mesenteric artery blood flow rose in a dose-dependent manner during the adrenaline infusions alone, but not during the infusion of adrenaline and propranolol [mean (95% confidence interval) area under the curve: control, -4.2 (-11 to +2.7)%; 10 ng of adrenaline min-1kg-1, +4 (-1 to 11.9)%; 40 ng of adrenaline min-1kg-1, +34 (+6.5 to +61.5)%; 10 ng of adrenaline min-1kg-1 and propranolol, -8.4 (-23 to +6)%]. 4. Superior mesenteric artery resistance fell during the adrenaline infusions alone and rose during the combined adrenaline and propranolol infusion [mean (SEM) area under the curve: control, 6.4 (2.7)%; 10 ng of adrenaline min-1kg-1, -2.9 (2.5)%; 40 ng of adrenaline min-1kg-1, -15 (1.4)%; 10ng of adrenaline min-1kg-1 and propranolol, 16.9 (10)%]. 5. These data suggest that splanchnic vasodilatation is mediated via a beta-adrenergic mechanism.

Adult↗
PubMed1993

Quality assurance of ultrasound imaging instruments by monitoring the monitor.

Ultrasound quality assurance (QA) is a means of assuring the constant performance of an ultrasound instrument. A novel 'ultrasound image analyser' has been developed to allow objective, accurate and repeatable measurement of the image displayed on the ultrasound screen, i.e. as seen by the operator. The analyser uses a television camera/framestore combination to digitize and analyse this image. A QA scheme is described along with the procedures necessary to obtain a repeatable measurement of the image so that comparisons with earlier good images can be made. These include repositioning the camera and resetting the video display characteristics. The advantages of using the analyser over other methods are discussed. It is concluded that the analyser has distinct advantages over subjective image assessment methods and will be a valuable addition to current ultrasound QA programmes.

Humans↗
PubMed1993

The development of equipment for the technical assessment of respiratory motion induced artefacts in MRI.

A device and technique to study the effects of respiratory motion on the quality of magnetic resonance images is proposed. The construction of the device enables a variety of test objects to be mounted and used in the evaluation of imaging parameters that may be affected by motion. The equipment is constructed of cast acrylic and the movement is actuated and controlled pneumatically thus ensuring that there are no interactions with the magnetic field and radiofrequency detection system to cause further image artefacts. Separate studies have been performed, using ultrasound, to assess the degree and rate of movement of organs owing to respiration in order to derive the motion parameters for the apparatus. Preliminary results indicate that the technique produces motion induced artefacts simulating those which are the result of the effects of respiration.

Diaphragm↗
PubMed1993

A comparative study of velocity measurements in major blood vessels using magnetic resonance imaging and Doppler ultrasound.

Velocity measurements in major blood vessels were obtained in studies of volunteers using magnetic resonance imaging (MRI) and compared with Doppler ultrasound (US). The vessels studied were the abdominal aorta, superior mesenteric artery, common carotid artery, superficial femoral artery and middle cerebral artery. Using a paired t-test, no significant difference was found between velocity values estimated by MRI and US (p > 0.08). The relative advantages of each technique in radiological practice are discussed.

Adult↗
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↗