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Biomedical subjects

R Skidmore

Publications and source records attributed to R Skidmore.

At least 37 records · Page 2Linked to original sources
PubMed1987

Application of computerised penile arterial waveform analysis in the diagnosis of arteriogenic impotence. An initial study in potent and impotent men.

A new method is described for evaluating arteriogenic impotence by means of noninvasive quantification of penile Doppler arterial waveforms using computerised analysis based on the Laplace Transform model. The haemodynamic changes occurring during a papaverine-induced erection in healthy potent volunteers have been recorded by this technique, which has also been shown to be capable of discriminating between a normal and an abnormal penile arterial supply in an initial study of potent and impotent men.

Adult↗
PubMed1987

Ductus arteriosus blood flow during first 48 hours of life.

A volumetric Doppler technique was used to measure net ductus arteriosus shunt during the first 48 hours of life in 30 infants of less than 33 weeks' gestation, and in 10 full term infants. In the full term infants a left to right shunt of 62 ml/kg/minute (95% confidence limits 43-82) shortly after birth decreased rapidly over the first 12 hours and was not measurable by 48 hours. The preterm infants had smaller left to right shunts shortly after birth--49 ml/kg/minute (95% confidence limits 38-59). There was no obvious subsequent change in the mean shunt, although by 48 hours there was greater variation in the size of the shunt. The respiratory distress syndrome did not affect the size of the ductal shunt, but the shorter the gestation period the larger the shunt by 48 hours. A ductal flow of greater than 70 ml/kg/minute at 48 hours of age predicted the subsequent development of a ductal murmur with 75% sensitivity and 100% specificity.

Blood Flow Velocity↗
PubMed1987

Vasoactivity of the major intracranial arteries in newborn infants.

Blood flow to the head and arms was measured by a new volumetric Doppler technique in 30 preterm infants and 10 full term infants. At least 80% of this blood flow is considered to perfuse the brain. At the same time mean blood velocity in the middle and anterior cerebral arteries was measured by Duplex Doppler scanning. While blood flow to the head and arms remained substantially constant in both groups over the first 48 hours of life (60 ml/100 g brain weight/min), blood velocity doubled in both cerebral arteries in the preterm group. The term infants had higher blood velocities in both arteries at all times, but the velocities also increased over 48 hours, although to a lesser extent than in the preterm group. These findings imply that the major intracranial arteries are themselves vasoactive, being dilated at birth and subsequently constricting, possibly as an autoregulatory response to rising arterial blood pressure. While vasodilated, the cerebral arteries will be less efficient at damping pressure transients, placing preterm infants at particular risk of periventricular haemorrhage during the early hours of life. The implications for possible approaches to the prevention of cerebral haemorrhage are discussed.

Arm↗
PubMed1986

A Doppler flowmeter for use in theatre.

We have developed a Doppler flowmeter based on a 10 MHz pencil probe and mean frequency estimator which overcomes many of the limitations of existing electromagnetic and ultrasonic flowmeters. The output of the flowmeter, which is proportional to the first moment of the Doppler power spectrum and hence mean blood velocity is linear from 1.3 to over 50 cm s-1 for pulsatile flow. Variation in vessel diameter and angle of insonation, which are the common sources of error in Doppler flowmetry, are minimised by constraining the vessel in a plastic cuff which fixes the probe angle at 50 degrees. A simple gauge is used to compress the vessel flat, before the cuff is applied, to measure the wall thickness to within 0.25 mm. The vessel internal diameter and hence blood flow can then be calculated using an experimentally determined calibration factor to compensate for non-even insonation. A range of sterilizable cuffs from 3-12 mm diameter have been built and the flowmeter is now being used routinely during all arterial reconstructive surgery. The accuracy and reproducibility of the system was tested for range of different sized silastic tubes on a hydraulic model and found to be less than 12% for vessels greater than 2 mm internal diameter. Satisfactory signals were easily obtained from all prosthetic materials with the exception of PTFE. The instantaneous output was compared to an electromagnetic flowmeter using a fast Fourier transform algorithm; the moduli of the harmonics were virtually identical but the Doppler system produced a smaller phase shift with increasing harmonics.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1986

Doppler ultrasound in the neonate.

The use of Doppler ultrasound to assess both the changing haemodynamics of the neonatal circulation and the perfusion of the brain is reviewed. The brain is particularly susceptible to both ischaemic and haemorrhagic injury in preterm and asphyxiated infants. However, the unique characteristics of the transitional neonatal circulation, and of the cerebral vasculature, pose considerable problems in the interpretation of Doppler signals from intracranial arteries. A volumetric Doppler method which eliminates some of those problems is discussed. The same method allows full assessment of the cardiovascular status of the newborn infant, including estimation of ductal shunting and left ventricular output. Doppler ultrasound, if used with a full understanding of the inherant assumptions and limitations of the particular methodology, is likely to prove invaluable in investigating pathological cerebral and cardiac vascular events in the newborn.

Brain↗
PubMed1986

Pulsatility index of superior mesenteric artery blood velocity waveforms.

A transcutaneous Doppler ultrasound technique was used to investigate superior mesenteric artery blood velocity waveforms in normal subjects. The shape of the waveforms was quantified by means of the pulsatility index (PI). The mean value +/- standard error of the mean of the PI measured in 82 normal subjects in the resting and fasting state was 3.57 +/- 0.11. There was no difference in the PI between sexes nor correlation between the PI and age. Following the ingestion of a meal in a group of 15 subjects the PI decreased by 46% (p less than 0.001). A significant fall persisted over the next two hours.

Adult↗
PubMed1986

Transcutaneous Doppler ultrasound measurement of superior mesenteric artery blood flow in man.

A duplex scanner which consists of a real time two dimensional scanner and a pulsed Doppler flowmeter was used to measure superior mesenteric blood flow in 70 healthy subjects. By processing the Doppler shift signals, the instantaneous average Doppler shift frequency and then the instantaneous average velocity of the flow rate were calculated. Both diameter of the vessel and angle between vessel and beam were measured from real time imaging. The mean (+/- standard error of the mean) of the superior mesenteric blood flow was 517 +/- 19 ml/min. There was neither significant difference in flow between sexes, nor correlation between flow and age (r = 0.042). The mean of coefficients of variability were 6.8% over the short term, and 8.2% in long term studies.

Adult↗
PubMed1985

Transcutaneous Doppler ultrasound measurement of coeliac axis blood flow in man.

Transcutaneous Doppler ultrasound was used to measure coeliac axis blood flow in 42 normal subjects in the fasting state and in 10 subjects following a liquid meal. A Duplex scanner was used and coeliac axis blood flow was estimated by calculating the instantaneous average velocity of blood flow over the cardiac cycle. Both the diameter of the vessel and the angle between the vessel and the beam were measured from real time imaging. The mean (+/- s.e.m.) of coeliac axis blood flow was 703 +/- 24 ml/min. There was no difference in the results between the sexes nor any correlation between flow and age. The mean coefficient of variability was 7.8 per cent in a 1 day test and 9.2 per cent in a 2 day test. Coeliac axis blood flow increased by 38 per cent immediately after the end of ingestion of the meal and declined to 29 per cent 5 min and 24 per cent 10 min later.

Adult↗
PubMed1985

Detection of early arterial disease: a study using Doppler waveform analysis.

Laplace transform analysis of arterial Doppler waveforms was examined for its potential in identifying subjects with early, pre-symptomatic arterial disease. Ninety men, aged 45 to 62, and with no history of cardiovascular disease, were selected from a population of 2300 involved in a longitudinal study of risk factors for cardiovascular disease. Forty-nine were selected on the basis of high values of Laplace delta, omega o, or both, and 41 were selected with "normal" values. Three years after initial screening examination, each was examined clinically and by exercise testing for evidence of arterial disease, and the waveform recordings were repeated. In the group with high waveform analysis values initially, 11 of 49 (22%) were found to have signs of arterial disease 3 years later, while among those with lower values only 2 of 41 (5%) had evidence of disease (p less than 0.05). Although variability of results obviates their use in monitoring the progress of individual subjects, this study supports the potential of Doppler waveform analysis for identifying a group of subjects with a high incidence of early arterial disease.

Arteriosclerosis↗
PubMed1984

The clinician and the vascular laboratory in the diagnosis of aortoiliac stenosis.

Two hundred and twenty-one lower limbs in 116 arteriopaths were examined for evidence of aortoiliac stenosis, by analyses of common femoral artery Doppler waveforms for pulsatility index (PI) Laplace delta, and principal components, pulse volume recordings (PVR) and thigh pressure measurements. Clinical assessment of the aortoiliac segment was also recorded in 124 limbs. The accuracy of prediction of aortoiliac stenosis, measured on biprojectional arteriograms, was calculated for the different methods, using multiple regression analysis. Considering all grades of stenosis together, clinical judgement was the best predictor of severity (R2 - the correlation coefficient squared = 0.66): addition of non-invasive tests increased the accuracy of prediction to R2 = 0.70. For stenoses greater than 50 per cent PVR amplitude was the best non-invasive test (R2 = 0.39), but was no better than clinical assessment (R2 = 0.40). However, for stenoses less than 50 per cent clinical judgement was poor (R2 = 0.13), and derived most benefit from addition of Laplace delta (R2 = 0.20) or PVR upstroke time (R2 = 0.26). In addition, common femoral PI and Laplace delta were compared in the arteriopaths, and in 146 limbs of normal control subjects, by calculation of sensitivity and specificity. PI was superior to Laplace delta for detecting severe stenoses and occlusions, but Laplace delta was more accurate in the detection of lesser degrees of disease. These results suggest that conventional clinical assessment is the best method for detecting aortoiliac stenoses greater than 50 per cent, but for less severe disease addition of vascular laboratory tests is helpful - especially PVR and Laplace waveform analysis.

Adult↗
PubMed1984

Analysis of femoral artery Doppler signals by LaPlace transform damping method.

The LaPlace transform damping (LTD) method of common femoral artery Doppler waveform analysis is a new method for assessing aortoiliac stenosis. A microcomputer was used to analyze the waveform to determine the value of the damping parameter, which is related to inflow stenosis. The study included 60 limbs with arterial disease and 20 limbs in normal control subjects. With a damping value of 0.60 used as the cutoff point between nonocclusive lesions and iliac stenoses of greater than 50% diameter reduction, we found a sensitivity of 100% and a specificity of 93% (overall accuracy 95%). Unlike Doppler waveform analysis by the pulsatility index method, the accuracy of the LTD method is not affected by occlusion of the superficial femoral artery. The Doppler signal processor and the computer currently used for the LTD analysis are simple to operate and fully suitable for routine use in a clinical vascular laboratory. Our experience indicates that the LTD method of waveform analysis provides the best noninvasive method for detection of significant inflow disease.

Aorta, Abdominal↗
PubMed1983

Differential diagnosis of arterial disease of the lower limb using Doppler ultrasound.

Doppler arterial waveforms from the femoral and ankle arteries of 55 normal control subjects and 76 arteriopaths were analysed for Laplace transform coefficients, delta and omega omicron, and pulsatility index (PI). At the femoral artery delta was superior to PI in accurately detecting mild and moderate aortoiliac stenosis, as assessed from arteriograms. In the femoropopliteal segment, the ratio of omega omicron from femoral to ankle level compared favourably with PI damping factor in the detection of occlusive disease. The Laplace transform system provides a helpful diagnostic method in lower limb arterial disease.

Aorta↗
PubMed1982

Transient ischaemic attacks: the static and dynamic morphology of the carotid artery bifurcation.

Studies evaluating the static and dynamic characteristics of the common carotid bifurcation are described. Slow motion angiographic frames, real time B-mode images and time position M-mode tracings have demonstrated appreciable vessel wall motion with an increase in distensibility at the carotid bulb compared to the proximal common carotid artery. Histopathological studies suggest that changes in the carotid artery elastin and collagen structure may contribute to the increased distensibility at the carotid bulb. The presence or absence of a cervical bruit did not correlate with the ultrasonic demonstration of plaque or blood flow turbulence. Mechanical factors relating to the development of symptoms of cerebral ischaemia are discussed.

Auscultation↗
PubMed1981

Department of Surgery, Bristol Royal Infirmary, U.K.

Recent developments in ultrasound techniques have made it possible to investigate patients with arterial disease non-invasively by using Doppler blood velocity signal analysis. Since January 1979, 189 patients were pre-stroke syndromes have been investigated by using pulsed Doppler and real-time B-mode ultrasound imaging and waveform analysis. The results were that both imaging systems were highly (more than 92%) sensitive and specific when compared with conventional carotid arteriography. The ultrasound systems detected turbulence and could also be used to measure the distensibility of the arterial wall. The results show that varying grades of carotid stenosis can be demonstrated by two ultrasonic imaging systems, and that lateral scans are particularly helpful.

Blood Flow Velocity↗
PubMed1981

Cigarette smoking: acute main and small vessel hemodynamic responses in patients with arterial disease.

While cigarette smoking is a major risk factor in lower limb ischemia, not all smokers develop symptomatic lesions, which suggests an individual susceptibility. Using Doppler probes the acute main vessel response to smoking was quantified in terms of the pulse transit time delay. Patients with occlusive arterial disease had a significant shortening in the transit time delay, suggesting a stiffening in the main vessels in response to smoking not seen in control subjects without disease. In patients with occlusive disease the digital pulse volume recorder amplitude decreased significantly in response to both low and high nicotine cigarettes, and these patients tended to self-titrate their nicotine intake, suggesting that little is to be gained by switching from high to low nicotine cigarettes: rather, cessation of smoking should be considered. These preliminary results suggest that patients with atherosclerotic occlusive disease are more susceptible to cigarette smoking and that Doppler or pulse volume recorder testing may help identify those habitual smokers who are at risk.

Adolescent↗