Abdominal aortic aneurysm detection by common femoral artery Doppler ultrasound waveform analysis.

The aim of this research was to determine the effects of abdominal aortic aneurysm (AAA) on blood flow patterns in the common femoral artery (CFA) and to determine the feasibility of detecting AAA by analysis of the CFA Doppler waveform. CFA Doppler waveforms were measured from 30 patients with AAA and 30 normal patients without significant atherosclerotic disease. On visual inspection of the CFA waveforms five features were noted, predominantly in the AAA group, as being different from a normal CFA waveform: (1) spectral broadening on the systolic down stroke; (2) transient velocity spikes on the systolic down stroke; (3) an irregular reverse flow pattern; (4) simultaneous forward and reverse flow; and (5) waveform elongation with the reverse flow component extending throughout diastole. Based on visual identification of these five features it was possible to predict AAA with 93% sensitivity and 70% specificity in patients without significant atherosclerotic disease.

A validated model of calf compression and deep vessel collapse during external cuff inflation.

This paper presents a validated model of calf compression with an external pressure cuff as used for deep vein thrombosis. Magnetic resonance (MR) images of calf geometry were used to generate subject-specific finite-element (FE) models of the calf cross section. Ultrasound images of deep vessel collapse obtained through a water-filled cuff were used to validate model behavior. Calf/cuff pressure interface measurements were applied to the FE model and the resulting tissue deformation was compared with MR image in normal volunteers (three females, four males, age range 20-55) using two distinct cuffs. MR observations and the model results showed good qualitative agreement. A similar reduction in cross-sectional area of the posterior tibial veins was obtained under both symmetric compression (89%) and asymmetric compression (81%), but greater compression of the anterior tibial veins was achieved with symmetric compression. The need to account for the effective compressibility of the calf tissue suggests that external measurements of the calf tissue deformation will not accurately predict deep vessel collapse. These results have implications for the modification of venous haemodynamics by such systems and could help to improve cuff design.

The effect of intermittent pneumatic compression on the bone uptake of (99m)Tc-labelled methylene diphosphonate in the lower limb.

INTRODUCTION: Venous compression of the lower limbs will obstruct outflow through the deep and superficial veins, yet inflow will continue, without continual swelling of the limb. It is hypothesised that venous channels in the long bones act as collateral channels to restore outflow, and therefore general blood flow through bone will increase. Such a hemodynamic change should affect the uptake of radiopharmaceuticals by the bone, though uptake changes in themselves would not definitely indicate flow changes. The purpose of this study, therefore, was to determine whether bone uptake in the lower limb is affected by intermittent venous compression, irrespective of the mechanism involved. MATERIALS AND METHODS: The effect of intermittent pneumatic compression of the thigh and calf on the uptake of (99m)Tc-methylene diphosphonate (MDP) was studied in 24 patients. All were undergoing routine bone imaging for medical conditions that were not focused on their lower limbs, and received 1 h of the therapy at 60 mmHg on one limb only, after injection of the radiopharmaceutical. Three hours after injection the relative difference in uptake (net counts per pixel) between the two limbs was calculated. The standard imaging protocol was otherwise unchanged. RESULTS: The median differences in uptake in the intermittently compressed limb compared with the contralateral limb were +7.6% (interquartile range +3.9% to +16.0%, p<0.0005 [Wilcoxon]) for the anterior aspect of the femur; +11.7% (interquartile range +4.3% to +22.2%, p<0.0005) posterior, femur; +10.5% (interquartile range +6.5% to +13.8%, p<0.0005) anterior, tibia; +10.6% (interquartile range +5.5% to +17.6%, p<0.0005) posterior, tibia. CONCLUSION: Intermittent pneumatic compression clearly and significantly increased the uptake of (99m)Tc-MDP in long bones. These data are consistent with increases in blood flow through bone, though a direct mechanical influence on the bone cannot be excluded. This effect should be given consideration during routine therapeutic and thromboprophylactic use of intermittent compression, and if the mechanism of the uptake changes can be established, their possible clinical uses should be investigated.

Development and validation of an in vivo analysis tool to identify changes in carotid plaque tissue types in serial 3-D ultrasound scans.

We have developed a three-dimensional (3-D) B-mode acquisition system suitable for imaging carotid plaques in vivo. A texture classification system using 157 statistical and textural algorithms, previously developed in our laboratory and shown to predict the contents of in vitro carotid plaques, was applied to in vivo 3-D image sets obtained from patients with both symptomatic and asymptomatic carotid artery plaques. Delineation of plaque boundaries is more difficult using in vivo images than in vitro images of excised plaques embedded in agar. This study has examined inter- and intraobserver variability studies to assess the degree of selectivity of the plaque region-of-interest (ROI) and assess the degree of repeatability for potential use in comparing serial scans. An interobserver limit of agreement of +/-12.9% and an intraobserver limit of repeatability of <2% were obtained. These results show that the plaque ROI selection is subjective, but is repeatable within acceptable limits.

Systemic haemostasis after intermittent pneumatic compression. Clues for the investigation of DVT prophylaxis and travellers thrombosis.

Intermittent pneumatic compression (IPC) is known to provide effective prophylaxis against post-surgical deep-vein thrombosis (DVT), and other procedures based on reducing venous stasis have been promoted recently to minimize the risk of thromboembolism after long-haul travel ('travellers thrombosis'). This study sought to measure the effects of IPC on systemic haemostasis, which are currently disputed. IPC was applied for 120 min on 21 male, non-smoking volunteers ranging in age from 19 to 47 years. IPC promoted a significant increase in global fibrinolytic potential. Levels of urokinase plasminogen activator activity (uPA) measured using an amidolytic assay were raised after IPC. However, enzyme-linked immunosorbent assays (ELISA) of uPA antigen, and the activities of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI-1) were not statistically different from those in control experiments. IPC led to highly significant falls in factor VIIa, associated with increased levels of tissue factor pathway inhibitor (TFPI). IPC enhances fibrinolysis and suppresses procoagulant activation. Measurements of specific fibrinolytic components do not reflect overall fibrinolytic activity and are highly dependent on the method of assay. The results provide important clues for detailed studies of the effects of haemodynamics on systemic haemostasis.

Analysis of the operation of the SCD Response intermittent compression system.

The work assessed the performance of the Kendall SCD Response intermittent pneumatic compression system for deep vein thrombosis prophylaxis, which claimed to set its cycle according to the blood flow characteristics of individual patient limbs. A series of tests measured the system response in various situations, including application to the limbs of healthy volunteers, and to false limbs. Practical experimentation and theoretical analysis were used to investigate influences on the system functioning other than blood flow. The system tested did not seem to perform as claimed, being unable to distinguish between real and fake limbs. The intervals between compressions were set to times unrealistic for venous refill, with temperature changes in the cuff the greatest influence on performance. Combining the functions of compression and the measurement of the effects of compression in the same air bladder makes temperature artefacts unavoidable and can cause significant errors in the inter-compression interval.

Relationship between ultrasound texture classification images and histology of atherosclerotic plaque.

Structure and content of atherosclerotic plaque varies between patients and may be indicative of their risk for embolisation. This study aimed to construct parametric images of B-scan texture and assess their potential for predicting plaque morphology. Sequential transverse in vitro scans of 10 carotid plaques, excised during endarterectomy, were compared with macrohistology maps of plaque content. Multidiscriminant analysis combined the output of 157 statistical and textural algorithms into five separate texture classes, displayed as ultrasound (US) texture classification images (UTCI). Visual comparison between corresponding UTCI and histology maps found the five texture classes matched with the location of fibrin, elastin, calcium, haemorrhage or lipid. However, histology preparation removes calcium and lipid and, so, can affect the structural integrity of atherosclerotic plaques. Soft tissue regions smaller than the UTCI kernel, (0.87 mm x 0.85 mm x 3.9 mm), such as blood clots, are also difficult to detect by UTCI. These factors demonstrate limitations in the use of histology as a "gold standard" for US tissue characterisation.

Neural network analysis of Doppler ultrasound blood flow signals: a pilot study.

It has been hypothesised that each artery in the human body has its own characteristic "signature" -a unique Doppler flow profile which can identify the artery and which may also be modified by the presence of disease. To test this hypothesis an artificial neural network (ANN) was trained to recognise three groups of maximum frequency envelopes derived from Doppler ultrasound spectrograms; these were the common carotid, common femoral and popliteal arteries. Data were collected from 24 subjects known to have no significant atheromatous disease. The maximum frequency envelopes were used to create sets of training and testing vectors for a backpropagation ANN. The ANN demonstrated a high success rate for appropriate classification of the test vectors: 100% for the carotid; 92% for the femoral; and 96% for the popliteal artery. This work has demonstrated the ability of the ANN to differentiate accurately between different and similar flow profiles, outlining the potential of this technology to identify subtle changes induced by the onset of arterial disease within a specific vessel. It should be noted that the ANN not only models the maximum frequency envelope but also, unlike standard indices, makes a decision as to which artery the maximum frequency envelope belongs to, thus providing the potential to obviate human subjective classification.

Bile acid dysfunction after clam enterocystoplasty.

OBJECTIVE: To determine if the bowel dysfunction that develops in approximately 12% of patients after a clam enterocystoplasty is due to disruption of the enterohepatic circulation of bile acids. PATIENTS AND METHODS: Fourteen symptomatic patients (mean age 36 years, range 21-65) who had undergone clam enterocystoplasty were investigated by bowel frequency charts, hydrogen breath tests of expired air and the retention of radioactive 75Se-labelled homocholic acid-taurine (SeHCAT), a synthetic bile acid. Patients with abnormal results were commenced on anion-exchange resins and the symptoms evaluated 6 weeks later. RESULTS: The interruption of bile acid circulation, as estimated by SeHCAT, occurred in most of the patients studied and was due to surgical resection of the terminal ileum. All hydrogen breath tests were normal, excluding bacterial overgrowth as a cause of diarrhoea. Bowel frequency correlated well with the percentage of SeHCAT retained. Anion-exchange resins were successful in relieving the symptoms if patients complied well with the treatment. CONCLUSIONS: After clam enterocystoplasty, some patients have bowel dysfunction caused by the interruption of the enterohepatic circulation of bile acids. These patients can be identified using bowel frequency charts and treated by anion-exchange resins.

Carotid artery duplex scanning: does plaque echogenicity correlate with patient symptoms?

In this study we have investigated the relationship between plaque sonolucency and ipsilateral hemispheric symptoms in 116 patients at risk of cerebrovascular disease (75 symptomatic patients, 41 asymptomatic patients). Our results indicate that plaque sonolucency is significantly associated with the incidence of patient symptoms at presentation. Twice as many symptomatic vessels contained the predominantly sonolucent plaque types (types 1 and 2) compared to contralateral asymptomatic vessels (p = 0.039, odds ratio = 2.9). Vessel stenosis also had a significant association with patient symptoms. No significant interaction was shown between vessel stenosis and plaque sonolucency (p = 0.15, odds ratio = 1.0). A model using vessel stenosis and plaque echogenicity as independent variables showed that degree of vessel stenosis had a closer association with incidence of symptoms (p = 0.03, odds ratio = 1.04) than plaque type (p = 0.13, odds ratio = 0.51).

Salivary gland tumours: is colour Doppler imaging of added value in their preoperative assessment?

Using a Toshiba SSA-270A Colour Duplex Scanner, 15 patients with suspected parotid and submandibular gland tumours had preoperative duplex scanning done. Peak systolic doppler shifts (fmax) were recorded and their vascularity was also subjectively scored. There were no arteries identified within the substance of contralateral normal glands. All recordings were analysed retrospectively and an independent histological assessment of tumours was made. Pleomorphic adenomas (n = 9) had a median peak systolic frequency (fmax) of 0.8 kHz, while adenolymphomas (n = 4) had a fmax of 1.65 and the two malignant tumours had fmax of 4.5 (P = 0.007 Kruskal-Wallis test). There appears to be a strong correlation between the fmax and the subjective vascular score (Corr 0.92). Colour duplex scanning is a non-invasive procedure which may be of help in the preoperative assessment of salivary gland tumours.

Postural changes in femoral artery blood flow in normal subjects, patients with peripheral vascular occlusive disease and patients undergoing lumbar sympathectomy, measured by duplex ultrasound flowmetry.

Regulatory peripheral vasoconstriction occurs in response to lower limb dependency. In mildly ischaemic limbs these responses are retained but are lost in patients with rest pain. Previously used methods have inherent difficulties when applied during postural change. We studied orthostatic responses in 12 normal subjects (aged 22-74 years, median 52 years) and 16 patients (aged 21-83 years, median 48 years) with mild and severe peripheral vascular disease using a duplex ultrasound flowmeter. In the normal subjects the 60-s mean common femoral artery volume flow values (ml min-1 +/- S.D.) were 77 +/- 83; -78 +/- 116; -190 +/- 136 for elevation, dependency and standing respectively. For claudicants (n = 7) the values were 18 +/- 37; -112 +/- 123; -216 +/- 103, respectively. In rest pain patients (n = 9) the responses were reversed, being -252 +/- 124; 131 +/- 89 and 184 +/- 85. Significant differences were apparent between elevation, dependency and standing flows, in each of the three groups (all p less than 0.0001). The rest pain group displayed characteristically different responses compared with both normal subjects and claudicants, for each postural change (p less than 0.0001 in all cases). Investigation of the dependency response was undertaken in eight further patients with rest pain before and after lumbar chemical sympathectomy and a characteristic pre-sympathectomy response predicted the clinical outcome.

Correlation between Korotkoff's sounds and ultrasonics of the brachial artery in healthy and normotensive subjects.

The clinical measurement of blood pressure is generally obtained by auscultation for Korotkoff's sounds over the brachial artery using a sphygmomanometer and cuff. Real-time two dimensional ultrasound and Doppler techniques were used to study the brachial artery movements and blood flow patterns during these pressure measurements. Simultaneous recordings of Korotkoff's sounds were obtained. A strong correlation in time was demonstrated between Korotkoff's five phases, brachial artery wall movements and specific blood flow patterns. The evidence largely supports what to date has been speculation as to the origin of Korotkoff's sounds in that Korotkoff's phases 1 and 3 appear to be produced by vigorous arterial wall motion and phase 5 by cessation of this movement. Phase 2 is produced by blood flow disturbance. Furthermore, the lack of correlation between phase 4 and any specific vascular event may go some way to explaining why in clinical practice phase 5 readings are now preferred for diastolic pressure.

Effect of postural change on common femoral artery volume flow, measured by duplex ultrasound, in normal subjects and patients with peripheral vascular disease.

Regulatory peripheral vasoconstriction occurs in response to adoption of the erect posture. Mildly ischaemic limbs are thought to exhibit near normal responses, but patients with rest pain show increases in blood flow on limb dependency. Previous methods of limb blood flow quantification (xenon clearance and venous occlusion plethysmography) have inherent difficulties when applied in these situations. We studied orthostatic responses in 12 normal subjects (aged 22-74 years (median 52) and 16 patients (aged 21-83 (median 48) with mild and severe peripheral vascular disease, using a duplex flowmeter system. In the normal subjects changes in the 60s mean, common femoral artery volume flow values were as follows (ml min-1 (1 SD]: 77 (83), -78 (116) and -190 (136), for elevation, dependency, and standing respectively. For claudicants (n = 7) the values were 18 (37), -112 (123) and -216 (103) respectively. In rest pain patients (n = 9) the responses were reversed, being -252 (124), 131 (89) and 184 (85) respectively. Significant differences were apparent between elevation, dependency and standing flows in each of the three groups (P less than 0.0001). Normal subject and claudicant responses on elevation and dependency differed significantly (P less than 0.0001 and 0.03 respectively). On standing, the responses were similarly significantly different. The rest pain group displayed characteristically different responses compared with both normal subjects and claudicants for each postural change (P less than 0.0001 in all cases). Duplex ultrasound volume flowmetry is non-invasive and offers an excellent method of quantifying physiological changes.

Normalization of thyroid blood flow in Graves' hyperthyroidism following radioactive iodine therapy.

In a group of 12 patients with Graves' hyperthyroidism, administration of 514 +/- 43 (mean +/- SD) MBq iodine-131 was associated with a fall of superior thyroid artery (STA) blood flow in two at 6 months and in eight at 11 months. The reduction in time-averaged velocity at 11 months correlated with the reduction in FT4 (r = 0.72, P less than 0.01) and in FT3 (r = 0.64, P less than 0.025) at this time. In four patients who had persistent elevated STA blood flow, two were still hyperthyroid. The diameter of the STA was unchanged at 6 months and only half the patients had reduction of their STA size at 11 months after radioiodine (RAI) therapy. These data indicate that normalization of STA blood flow precedes normalization of STA size in patients treated with RAI. Further work is required to determine whether STA blood flow measurements are of predictive value in treatment outcome.

Common femoral artery volume flow in peripheral vascular disease.

Common femoral artery volume flow was measured at rest and during postocclusive reactive hyperaemia in 80 normal subjects and 67 patients with radiological evidence of occlusive peripheral vascular disease. At rest, means(s.d.) common femoral artery volume flow in normal subjects (344(135) ml/min) and all patients with peripheral vascular disease (401(168) ml/min) was not significantly different. During postocclusive reactive hyperaemia, mean(s.d.) peak flow was significantly higher in normal subjects (1951(438) ml/min) than in patients with peripheral vascular disease (996(457) ml/min) (P less than 0.01). Common femoral artery volume flow in patients with critical ischaemia and intermittent claudication did not differ at rest but mean(s.d.) peak flow in patients with critical ischaemia (697(276) ml/min) was significantly lower than in claudicants (1131(447) ml/min) (P less than 0.01). Mean(s.d.) resting common femoral artery volume flow in limbs with femoropopliteal disease (457(185) ml/min) was significantly greater than that in limbs with occlusion of the aortoiliac segment (308(130) ml/min) (P less than 0.01). However, this difference did not persist during postocclusive reactive hyperaemia. A hyperaemic index, calculated from the hyperaemic responses to below knee and whole limb ischaemia, was used to quantify segmental perfusion during postocclusive reactive hyperaemia. The mean(s.d.) value in normal subjects, 46(9) per cent, and in those with aortoiliac disease, 52(12) per cent, indicated approximately equal perfusion of the above and below knee limb segments. In those with femoropopliteal disease the mean(s.d.) hyperaemic index was 17(13) per cent, revealing relative hypoperfusion of the below knee segment.

Duplex scanning in suspected vasculogenic impotence: a worthwhile exercise?

The value of duplex scanning in the assessment of impotence was evaluated in 146 impotent men. Scanning was by means of a Diasonics DRF 400 and penile artery measurements were taken before and after the intracorporeal injection of papaverine hydrochloride. The penile/brachial index was measured in 82 patients and its predictive value compared with the results of duplex scanning and papaverine-induced erection. On scanning evidence of good arterial inflow but poor erections, indirect evidence of venous leakage was assumed. The results showed that the deep artery responses best characterised the erectile response, with the dorsal artery being less helpful. All 37 patients with full erections following papaverine exhibited bilateral deep artery peak velocities of greater than or equal to 25 cm/s. Of the remaining 109 sub-optimal responders, 17 also has this finding; all had undergone dynamic cavernosography, with 16 exhibiting venous leakage. The penile/brachial index was found to classify 13 patients incorrectly. A critical value of deep artery response to attain erection is postulated, enabling more logical use of cavernosography. The penile/brachial index was shown to be suspect and it was concluded that duplex scanning is a useful, non-invasive method in the assessment of impotence.

Nifedipine in patients with peripheral vascular disease.

The calcium antagonist nifedipine has been studied in a group of patients with intermittent claudication. In a long-term double blind, placebo controlled trial in 27 patients there was no effect on exercise tolerance as measured by pedal ergometry and only a limited improvement in symptom score on double dose nifedipine. Common femoral artery volumetric blood flow (measured by duplex ultrasound) was unaffected. The acute effects on blood flow were also studied, with a mean increase of 23% in common femoral artery blood flow 30 min after sublingual nifedipine. The administration of nifedipine to patients with peripheral vascular disease will not adversely affect claudication symptoms, and may result in an acute improvement in lower limb blood flow. Nifedipine is a suitable antihypertensive in patients who suffer from intermittent claudication.

Characterisation of the atheromatous plaque in the carotid arteries.

Ultrasound duplex scanning is one of the major methods for the study of the development of the atherosclerotic plaque. The pulsed Doppler flowmeter can be used to investigate the flow disturbance caused by the presence of the atherosclerotic plaque in the flow lumen. The high resolution image capability means that the morphology and structure of the plaque may be studied in detail and comparisons made between the ultrasound appearance and histology, at carotid endarterectomy. The real-time image capability allows the study of the motion of the plaque over the cardiac cycle. The bending and shearing motions observed in some plaques may be a contributory factor to the fissuring and cracking, ulceration and intra-plaque haemorrhage, observed. It is felt that the dynamics of the plaque and its environment have largely been overlooked and that in order to investigate further the natural history of the plaque, it is necessary to investigate plaque morphology and structure, plaque dynamics, and the consequent flow disturbance.