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Biomedical subjects

A J Thrush

Publications and source records attributed to A J Thrush.

17 recordsLinked to original sources
PubMed2000

A comparison of colour duplex ultrasonography, papaverine testing and common femoral Doppler waveform analysis for assessment of the aortoiliac arteries.

OBJECTIVE: to study the "accuracy" of aortoiliac colour duplex ultrasonography. DESIGN: prospective study. SETTING: vascular laboratory, University Hospital. METHODS: a total of 25 aortoiliac stenoses were studied in 23 patients. For each iliac segment, colour duplex ultrasound, papaverine testing, hyperaemic common femoral Doppler waveform analysis and hyperaemic testing using a thigh pressure cuff were performed. A velocity ratio of two was used to indicate a significant 50% diameter-reducing stenosis, but the velocity differences across stenoses as well as various characteristics of the hyyperaemic common femoral waveform were also studied. Retrospective receiver-operator characteristics and Kappa values were used for analysis. RESULTS: the Kappa agreement between ultrasonography and papaverine testing was 0.12 using peak systolic velocity ratios and 0.8 using hyperaemic peak systolic velocity differences. Hyperaemic common femoral pulsatility (PI) and resistance index (RI) both gained a Kappa level of 0.60. The reactive hyperaemia produced by a thigh cuff was more pronounced than that produced by papaverine. CONCLUSION: although the velocity ratio did not appear to perform well against the papaverine test, its apparent over-sensitivity calls into question the sensitivity of papaverine testing itself. The hyperaemic velocity difference at the stenosis or the hyperaemic PI or RI at common femoral level appear useful, non-invasive indicators of significant aortoiliac arterial disease.

Aged↗
PubMed1998

The increasing activity of a vascular ultrasound service.

OBJECTIVES: To examine the change in activity of a vascular ultrasound service over 7 years. DESIGN: Retrospective review. SETTING: Vascular studies unit, University hospital. METHOD: Audit of the number of vascular ultrasound tests carried out over the last 7 years using a prospective computerised database. RESULTS: Data shows that the overall workload has tripled over the 7-year period. In addition the complexity of investigations has increased during this time. The number of carotid scans has increased four-fold while the number of graft surveillance scans and vein scans has increased seven-fold. Assessment of lower limb arteries has developed from simple pressure measurements to detailed ultrasound scans and, as a consequence, the number of diagnostic angiograms has fallen by 75%. The factors that have influenced these changes are discussed. CONCLUSIONS: There has been an important increase in the role of colour Doppler ultrasound as it becomes the "first line" vascular diagnostic test. However this trend can only continue if vascular ultrasound services are appropriately resourced. It is therefore essential to maintain an efficient audit system.

Angiography↗
PubMed1998

Role of saphenous vein surgery in the treatment of venous ulceration.

BACKGROUND: This paper describes local anaesthetic saphenous disconnection in elderly patients for the treatment of venous ulceration in legs with either saphenous venous reflux alone or in combination with deep venous reflux. METHODS: Ambulatory venous pressure was measured in 16 legs with saphenous vein reflux alone and in nine legs with combined deep and saphenous venous reflux before, immediately after and 3 months after saphenofemoral or popliteal disconnection. Ulcer area was measured by computerized planimetry before surgery and at 1 and 3 months after operation. No compression bandages or hose were applied after surgery unless the ulcers had not begun to heal after 1 month. RESULTS: In legs with saphenous reflux alone all ulcers healed without compression bandages at a median of 81 (range 14-253) days and the pressure relief index (PRI) improved significantly both after surgery and at follow-up. None of the ulcers in the nine limbs with saphenous and deep venous reflux healed without compression bandaging and the PRI was unchanged immediately following surgery and at follow-up. CONCLUSION: Saphenous vein disconnection improves venous function and heals venous ulcers without compression bandaging if the deep veins are normal. This procedure under local anaesthetic may be particularly suitable for elderly patients, but long saphenous vein stripping should be added in young patients.

Aged↗
PubMed1997

An evaluation of the potential and limitations of three-dimensional reconstructions from intravascular ultrasound images.

Three-dimensional (3D) reconstructions of arteries can be produced using two-dimensional (2D) intravascular ultrasound (IVUS) images. Any artefact that affects 2D images has the potential to limit the quality of a 3D reconstruction. Using a catheter withdrawal technique, a range of test rigs were used to assess: (i) the effect of rotation of the probe orientation; (ii) the ability to reconstruct the true path of a tortuous vessel; (iii) the effect of image distortion on diameter measurements; (iv) the number of images per unit length used to produce a 3D reconstruction; and (v) the quality of the IVUS 3D reconstruction of a stent. These investigations show that 3D IVUS imaging is prone to artefacts. For 3D IVUS images to be used to quantify the vessel path or to make accurate measurements of vessel dimensions, more information about the catheter tip position and orientation is required than is currently available with the pullback technique.

Humans↗
PubMed1996

Ambulatory venous pressure: correlation with skin condition and role in identifying surgically correctible disease.

OBJECTIVES: (1) To evaluate the full spectrum of venous skin damage with respect to ambulatory venous pressure. (2) To determine whether the ambulatory venous pressure/tourniquet test can be used to select patients for superficial venous surgery (eg. long or short saphenous stripping). DESIGN: Prospective study. SETTING: Vascular studies unit. MATERIALS AND METHODS: Ambulatory venous pressure was measured in a larger sample of limbs (360) with a wide spectrum of venous disease. In addition the effect of a tourniquet placed below the knee on ambulatory venous pressure and venous refilling time was assessed in 234 limbs. This was compared with Duplex assessment of deep and superficial venous reflux at this site. RESULTS: There was a linear trend towards more severe skin damage with increasing ambulatory venous pressure. Ulceration was associated with more severe calf muscle pump dysfunction (higher ambulatory venous pressure) than were lipodermatosclerosis, eczema or pigmentation. The tourniquet test was not able to distinguish between deep and superficial reflux as determined by Duplex scanning. CONCLUSIONS: Ambulatory venous pressure should be used to quantify venous insufficiency and remains the reference standard test of the venous calf muscle pump. The tourniquet test should not be used to select patients for surgery since it cannot distinguish deep from superficial venous incompetence. Venous reflux is best localised using Duplex ultrasound.

Blood Pressure Monitoring, Ambulatory↗
PubMed1996

Measurement of resolution in intravascular ultrasound images.

Detailed images of arteries can be formed by inserting intravascular ultrasound (IVUS) catheters within them. These catheters contain rotating ultrasound transducers and are capable of displaying disease and features such as the layers of artery walls. There is, however, relatively little information available on IVUS resolution even though this is necessary to interpret the images. Techniques for assessing IVUS resolution in three dimensions are described for a 20 MHz Boston Scientific catheter and a Diasonics IVUS scanner as well as the results obtained. Out-of-plane resolution was measured by finding the ultrasound beam thickness. Axial and lateral resolution were assessed by the minimum separation of two point targets when their images could just be distinguished. The out-of-plane resolution was found to improve slightly with distance from the catheter, varying from 2.0-1.5 mm. Lateral resolution worsened in a linear manner with distance. At a distance of 5 mm from the catheter, lateral resolution was 0.83 mm. The axial resolution was the best of the three resolutions and was actually limited by the screen display scale. With the highest magnification the axial resolution was approximately 0.19 mm and was constant with distance.

Arteries↗
PubMed1996

The development of an in vitro flow model of human saphenous vein graft intimal hyperplasia.

OBJECTIVE: Although the role of blood flow has been investigated in animal models of intimal hyperplasia, there have been no detailed studies in intact human vein owing to the difficulties in designing a suitable laboratory model. The aim of this study was to develop a flow model of human vein graft intimal hyperplasia. METHODS: Organ cultures of human saphenous vein were exposed to laminar flow by culturing in a closed circulatory system under predetermined conditions of venous and arterial shear stress for 14 days. Following fixation and processing, paraffin sections were immunostained and neointimal thicknesses measured. RESULTS: It was found that arterial flow completely inhibited neointima formation, but venous flow only partly suppressed the response when compared with vein cultured under static conditions. These results are in agreement with previous in vivo studies in a primate graft model, where increased shear stress inhibited intimal proliferation. CONCLUSION: The endothelial cell is believed to be the key mediator of haemodynamic effects which influence smooth muscle cell proliferation, and the flow rig developed in this study offers the potential to study inter-cellular interactions within the intact vessel. Furthermore, this method provides the facility to study the effects of different flow conditions on segments of vein from the same patient. This model has scope for further development and sophistication which may ultimately lead to increasing our understanding of the aetiology of vein graft stenoses, and hence formulation of preventative strategies.

Culture Techniques↗
PubMed1993

Venous assessment using air plethysmography: a comparison with clinical examination, ambulatory venous pressure measurement and duplex scanning.

Air plethysmography was compared with clinical assessment, ambulatory venous pressure measurement and duplex ultrasonography in 103 unselected limbs with venous disease and ten normal control limbs without such disease. Measurements of venous function obtained by air plethysmography showed considerable overlap between groups of limbs classified on the basis of clinical condition or by the presence of popliteal incompetence detected by duplex scanning. The measurement of venous refilling time using air plethysmography correlated poorly with that obtained by venous cannulation (rs = 0.58). The residual volume fraction did not correlate with ambulatory venous pressure measurement (rs = 0.04). Air plethysmography was not found to be as useful as previously reported. The residual volume fraction should not be accepted as a substitute for ambulatory venous pressure measurement, which remains the 'gold standard' test of venous function.

Blood Pressure Determination↗
PubMed1992

Transcutaneous ultrasound measurement of blood-flow in internal mammary artery to coronary artery grafts.

Transcutaneous doppler ultrasound was used to examine internal-mammary-artery (IMA) blood-flow in 26 patients with IMA coronary bypass grafts. The ungrafted right IMA could be seen in all of 19 patients, the grafted left IMA in 16 of 26, and the grafted right IMA in 3 of 7. The velocity profile recorded from the proximal part of the grafted IMA is distinct from that of an ungrafted artery, with a systolic peak which reflects graft capacitance in the face of high intramyocardial resistance, and a diastolic peak which represents graft conductance when intramyocardial resistance is low. Total graft blood-flow can be estimated from the mean velocity and the measured vessel diameter; resting flows ranged from 22 to 79 ml/min. In recently grafted patients, resting graft blood-flow correlated with myocardial "run-off" estimated from preoperative arteriograms; graft blood-flow increased appropriately with exercise. This simple, non-invasive technique to measure IMA graft blood-flow may find applications for routine postoperative follow-up of patients with IMA grafts and for studies on the physiology and pharmacology of coronary artery blood-flow.

Blood Flow Velocity↗
PubMed1992

Intensive blood flow monitoring following femoro-distal bypass: can early outcome be reliably predicted?

Forty-two femoro-distal vein grafts were studied in the early post-operative period for up to 1 week using a newly developed Doppler monitoring system designed to make frequent, automatic assessments which were stored on tape. Thirty-three grafts remained patent at 1 month with clinical improvement but in nine cases, all performed for critical ischaemia, reconstruction was unsuccessful with six grafts thrombosing and three remaining patent without clinical improvement (haemodynamic failure). The system was shown to provide good quality data, subsequent analysis of which with respect to the time-averaged mean velocity (TAMV) and pulsatility index (PI) revealed good separation between successful and failed grafts. In 30/33 cases a good result was predicted by the early establishment of hyperaemic flow (TAMV greater than 10 cm s-1, PI less than 2), whereas in three a "low flow" state was observed (TAMV less than 10 cm s-1, PI 2-3) which also resulted in a successful outcome. Graft thrombosis was heralded by the rapid development of high pulsatility (PI greater than 6) or a progressive departure from initial hyperaemia towards more pulsatile flow within a few days. Haemodynamic failure was associated with poor flow (TAMV less than 10 cm s-1) accompanied by a PI greater than 3.5. Intensive post-operative monitoring with this new system offers a means whereby early graft outcome can be reliably predicted and also has the potential to study the effects of any intervention used to salvage high risk grafts.

Blood Flow Velocity↗
PubMed1991

Perioperative monitoring of blood flow in femoroinfragenicular vein grafts with Doppler ultrasonography: a preliminary report.

A system for monitoring blood flow in femorodistal vein grafts with Doppler ultrasonography in the immediate postoperative period has been developed. Twenty-three grafts have been monitored for periods of up to 72 hours. Seventeen grafts have remained patent at minimum follow-up of 6 months, and six grafts occluded in the immediate postoperative period. Successful Doppler recordings were obtained in 16 successful and all failed grafts. Fast Fourier transform analysis of the Doppler signals was performed, and pulsatility index and time-averaged mean velocity were derived from the spectral information. Successful grafts displayed hyperemic flow with pulsatility index less than 2 and time-averaged mean velocity greater than 10 cm/sec. Failed grafts could be classified in two groups: those that occluded less than 24 hours after operation and those that occluded after 24 hours after operation. Short-term failure was categorized by highly pulsatile flow, with pulsatility index rising rapidly and time-averaged mean velocity falling correspondingly before actual cessation of flow. Delayed failure was less well defined but was suggested by failure to develop, or early deviation from, the hyperemic flow seen in successful grafts. Occlusion was heralded by development of the pulsatile pattern seen in the short-term failure group.

Blood Flow Velocity↗
PubMed1990

Portable directional ultrasonic Doppler blood velocimeter for ambulatory use.

The design of a portable directional Doppler velocimeter and of purpose-built probes intended for monitoring blood flow in femorodistal bypass grafts in ambulatory patients are described. The design is based on a continuous-wave Doppler technique with quadrature demodulation. The Doppler unit was interfaced to a 'personal-stereo' recorder to store the Doppler signals. The advantages and the limitations of recording flow in ambulatory patients are discussed. Examples of blood flow data collected from femorodistal bypass grafts are given.

Arteries↗
PubMed1986

A comparison of mercury and digital clinical thermometers.

A primarily clinical trial has been undertaken to investigate and compare the use of mercury and digital thermometers in a ward situation. Both laboratory and clinical studies show that there is no significant difference in the average accuracy of the two types of thermometers, however there is a greater fluctuation of readings of temperature when using electronic thermometers. In clinical studies between 9 and 23% of repeated measurements using an electronic thermometer differ by 0.5 degrees C or more whilst the corresponding range for mercury thermometers is 0.6%. It is also shown that when making clinical measurements with mercury thermometers there is no clinical advantage in using a measurement time longer than 3 minutes.

Body Temperature↗