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Biomedical subjects

A R Naylor

Publications and source records attributed to A R Naylor.

At least 55 records · Page 3Linked to original sources
PubMed2002

Complications following peripheral angioplasty.

BACKGROUND: Peripheral angioplasty is increasingly the first choice intervention in patients with peripheral vascular disease. The aim of the current study was to audit prospectively all major complications, especially the requirement for emergency surgical intervention. PATIENTS AND METHODS: A prospective audit of outcome after peripheral angioplasty in 988 patients undergoing 1377 interventional procedures between 1 October 1995 and 30 September 1998 at which 1619 vessel segments were angioplastied. RESULTS: Major medical morbidity (bronchopneumonia, stroke, renal failure, myocardial infarction) complicated 33/1377 procedures (2.4%). Emergency surgical intervention was required after 31/1377 procedures (2.3%) with the commonest aetiologies being acute limb ischaemia and haemorrhagic complications. The amputation rate following angioplasty was 0.6% and no patient presenting with claudication or graft complications underwent amputation. The amputation rate following angioplasty for critical limb ischaemia was 2.2%. Overall, the risk of death and/or major medical complication and/or requiring emergency surgical intervention was 3.5%. The rate of complications was no different for subintimal as opposed to transluminal angioplasties. CONCLUSIONS: Peripheral angioplasty is associated with a low risk of major medical and surgical complications.

Amputation, Surgical↗
PubMed2002

Deterioration in carotid baroreflex during carotid endarterectomy.

OBJECTIVE: Blood pressure instability after carotid endarterectomy (CEA) has been associated with a disturbance of the baroreflex control mechanism caused by the surgery in the carotid sinus region. The purpose of this study was to determine if a deterioration in carotid baroreceptors occurs during the surgery. METHOD: Heart rate (HR) and blood pressure (BP) were recorded continuously in 60 patients undergoing CEA as well as preoperatively and postoperatively at 2 days and 6 weeks. The baroreflex sensitivity was determined by cross-spectral analysis of HR and systolic blood pressure (SBP). During the surgery, three tests were used to assess the baroreflex response. The first test simulated a sudden fall in systemic blood pressure by clamping the common carotid artery. The second test simulated a rise in systemic blood pressure by applying pressure by using a rubbing action on the luminal surface of the carotid sinus region. The rub test was performed twice, once with the atheromatous plaque in situ and once when the plaque had been removed. The third test is clamp removal and restoration of blood flow through the carotid sinus. RESULTS: Carotid cross-clamping increased mean +/- standard error of the mean SBP from 117 +/- 3 mm Hg before clamping to 125 +/- 3 mm Hg (P <.05) at 30 beats after clamping. The first rub test with the plaque in situ decreased SBP from 121 +/- 3 mm Hg to 117 +/- 3 mm Hg (P <.01) at 10 beats after the rub test, indicating a functioning baroreceptor reflex. The second rub test increased SBP from 126 +/- 3 mm Hg to 128 +/- 3 mm Hg (P <.05). SBP dropped (P <.01) when unclamping suggesting a selective alteration of the baroreflex sensitivity. The baroreflex sensitivity was significantly reduced 2 days postoperatively when compared to preoperative values (P <.05). CONCLUSIONS: These findings suggest that the act of plaque removal could be associated with a partial disruption of baroreceptor mechanism in the carotid artery. This could affect type I baroreceptors.

Aged↗
PubMed2001

Automated embolus identification using a rule-based expert system.

Transcranial Doppler ultrasound (US) can be used to detect microemboli in the cerebral circulation, but is still limited because it usually relies on "human experts" (HEs) to identify signals corresponding to embolic events. The purpose of this study was to develop an automatic system that could replace the HE and, thus, make the technique more widely applicable and, potentially, more reliable. An expert system, based around a digital signal-processing board, analysed Doppler signal patterns in both the time domain and frequency domain. The system was trained and tested on Doppler signals recorded during the dissection and recovery phases of carotid endarterectomy. It was tested with 74 separate 2.5-min recordings that contained at least 575 artefacts in addition to 253 s of diathermy interference. The results were compared with the results obtained by three HEs. Using a "gold-standard" that classified any event detected by the majority of HEs as an embolus, the automatic system displayed a sensitivity of 94.7% and a specificity of 95.1% for 1151 candidate events 7 dB or more above the clutter (signal-to-clutter ratio, SCR, > or = 7 dB), and 89.6% and 95.3%, respectively, for 2098 candidate events with SCR > or = 5 dB. The system had a very similar performance to individual HEs for SCR > or = 7dB, and was only marginally worse for SCR > or = 5 dB.

Artifacts↗
PubMed2001

Plasma MMP-9 - a marker of carotid plaque instability.

OBJECTIVES: to investigate whether peripheral blood levels of matrix metalloproteinases (MMPs) or their inhibitors are altered in patients with particulate cerebral embolisation. DESIGN: a prospective study. MATERIALS AND METHODS: using sandwich enzyme immunoassay, plasma levels of MMPs-1, -2, -3 and -9, plus TIMPs-1 and -2 were quantified in 70 consecutive patients undergoing carotid endarterectomy. Patients were monitored with transcranial Doppler (TCD) preoperatively and during the dissection phase of the operation to detect those with spontaneous particulate embolisation (n =21). RESULTS: the plasma level of MMP-9 was significantly higher in those patients with evidence of spontaneous embolisation compared to those without. There were no differences in other MMP levels, or plasma concentrations of TIMPs. CONCLUSIONS: plasma MMP-9 levels are elevated in patients with particulate cerebral embolisation, and this may represent a novel marker of atherosclerotic plaque instability.

Aged↗
PubMed2001

A prospective audit of complex wound and graft infections in Great Britain and Ireland: the emergence of MRSA.

BACKGROUND: a number of studies have examined the outcome of complex wound and graft infections, but most include small numbers of patients collected over a prolonged period of time. To date, there is little information on the clinical outcome of infections involving methicillin-resistant Staphylococcus aureus (MRSA). METHODS: between February 1998 and January 1999, two prospective multi-centre audits were performed in order to examine the current outcomes following (1) complex vascular wound infections and (2) graft infections in Britain and Ireland with particular reference to outcome associated with MRSA infection. RESULTS: seventy-five complex wound infections (Szylagyi II and III) were reported, with the commonest single organism being MRSA. Type II infections were associated with a 5% risk of death and/or amputation as opposed to 75% in those with a type III infection. Fifty-five graft infections were reported, with the commonest single organism being MRSA. Overall, 30 (55%) died or underwent amputation. MRSA wound and graft infections were associated with a significantly higher risk of amputation and prolonged hospital stay (but not of death) as compared with MRSA negative patients. CONCLUSIONS: in this audit, MRSA was the commonest single organism cultured in patients with complex wound and graft infections after vascular surgery. This represents a major change in the spectrum of causative organisms relative to other, older published series. MRSA infections contribute towards an increased risk of adverse outcome and prolonged hospital stay.

Cross Infection↗
PubMed2001

The impact of MRSA on vascular surgery.

OBJECTIVES: To investigate the prevalence of MRSA infection in patients treated in a major vascular unit and examine its consequences. DESIGN AND METHODS: A retrospective case-note review was performed. RESULTS: During the period 1993 to 2000, a total of 172 patients (4.4% of total) were positive for MRSA. Of these 97 were colonised and 75 were infected by MRSA. The proportion of wound or graft infections caused by MRSA has increased (4% in 1994 to 63% in 2000). Three patients developed native artery infection (one following aortic stent insertion and 2 following embolectomy). All patients with aortic graft infection died. All patients with infected prosthetic infrainguinal bypass ended up with an amputation. CONCLUSION: The prevalence of MRSA infection is increasing. Infection of aortic grafts appears to be uniformly fatal and lower limb graft infection is associated with high limb loss.

Female↗
PubMed2001

Patients' thromboembolic potential between bilateral carotid endarterectomies remains stable over time.

OBJECTIVES: There is limited understanding of the reasons underlying post-CEA carotid thrombosis. Clinicians have often implicated operative technique, such as patch type or shunting, however the evidence for this is limited. We have studied whether it is the patients themselves who are prothrombotic, by studying the rates of emboli detection in patients undergoing bilateral CEAs at separate time points. MATERIALS AND METHODS: Sixteen patients (3 women) underwent CEA during the study period, all of whom were taking aspirin. CEA was performed in a standardised manner throughout the study. All patients were monitored for 3 h postoperatively using a 2 MHz fixed head probe. RESULTS: Those patients who had no emboli detected on TCD after the first operation, had a mean of 2.5 emboli after the second operation. Patients with emboli after the first operation had a mean of 41.3 emboli after the second CEA (MWU test, p=0.02). The dose of aspirin administered did not affect emboli rates. Correlation of the number of emboli detected after the first CEA with the second CEA gave a significant correlation ( p=0.038). CONCLUSIONS: There appear to be factors relating to the patient that places some individuals at an increased risk of thrombotic stroke. Further elucidation of these factors may enable more effective, targeted therapy to be applied in the prevention of arterial thrombosis.

Aspirin↗
PubMed2001

Randomized trial of vein versus Dacron patching during carotid endarterectomy: influence of patch type on postoperative embolization.

PURPOSE: A recent overview indicated that although routine patching is safer than routine primary closure after carotid endarterectomy (CEA), there is no systematic evidence that patch type influences outcome. However, most surgeons still believe that prosthetic patches are probably more thrombogenic than vein patches. This study tested the hypothesis that there was no difference in thrombogenicity between the different patch types. METHODS: A total of 274 patients undergoing 276 CEAs were randomized to either Dacron-patch closure (n = 137) or vein-patch closure (n = 139). All patients with an accessible cranial window were monitored for 3 hours postoperatively with transcranial Doppler scanning (TCD). The number of emboli and rate of embolization were quantified with the requirement for selective dextran therapy to control high rates of postoperative embolization. All patients were assessed postoperatively and again at 30 days by a neurologist, and all patients underwent a duplex examination at 30 days. RESULTS: The 30-day death/any stroke rate was 2.2% for patients in the Dacron-patch group and 3.6% for patients in the vein-patch group (P =.72). Patients in the Dacron-patch group had a higher incidence of postoperative emboli (median, 5; interquartile range, 0-10.5) than patients in the vein-patch group (median, 3; interquartile range, 1-17; P =.028). However, the incidence of detecting more than 50 emboli was virtually identical, and patch type had no effect on the incidence of high-rate, sustained embolization that required dextran therapy (5.3% for Dacron, 3.7% for vein). No patient had a carotid thrombosis at 30 days. CONCLUSION: Sustained, high-rate embolization, previously shown to be highly predictive of progression to carotid thrombosis, appears to be patient dependent, rather than related to patch type.

Aged↗
PubMed2001

A parametric approach to measuring cerebral blood flow autoregulation from spontaneous variations in blood pressure.

Autoregulation maintains cerebral blood flow (CBF) almost constant in the face of changes in arterial blood pressure (ABP). Tests for impairment of this process using only spontaneous fluctuations in ABP, without provoking large variations, are of great clinical interest, and a range of different approaches have previously been applied. Extending earlier work based on linear filters, we propose a simple parametric method using a first order finite impulse response filter. We evaluate the method on ABP and CBF velocity [(CBFV), from trancranial Doppler ultrasound] signals collected in 60 patients with stenosis or occlusion of the carotid arteries. Data were collected during the inspiration of ambient air, a 5% CO2/air mixture, and finally the return to ambient air. Equivalent data were collected in 15 normal subjects. The filters estimated from the data segments with constant inspiratory pCO2 showed the expected high-pass characteristic, which was reduced during hypercapnia and also in patients. Highly significant correlation between the filter parameters and cerebrovascular reactivity (percent increase in CBFV per unit change in end-tidal pCO2) gives further evidence that the filters reflect autoregulation. The method allows simple parametrization of the dynamic autoregulatory responses in CBFV, and the analysis of short (1 min) data segments.

Aged↗
PubMed2000

Simple and reliable method of doxycycline determination in human plasma and biological tissues.

Over recent years there has been a resurgence in the use of doxycycline in clinical practice, which does not depend on its antibacterial properties. This paper describes a method of determination of doxycycline in human plasma and atheromatous tissue using high-performance liquid chromatography (HPLC), and a cheap commercially available extraction system. Doxycycline is extracted in the mobile phase and injected directly into the HPLC system, avoiding time consuming drying up steps. A limit of detection of 0.125 microg/ml of plasma, and a relative standard deviation of 3% was achieved, making the method very reliable and useful for assays within the usual therapeutic range. The method has also been applied to the extraction of a mixture of tetracyclines from plasma and atherma with equal efficacy, making it useful for assays of this class of drugs in veterinary practice and assays of food contaminants.

Anti-Bacterial Agents↗
PubMed2000

Estimating normal and pathological dynamic responses in cerebral blood flow velocity to step changes in end-tidal pCO2.

The regulation of cerebral blood flow (CBF) following changes in arterial blood pressure (ABP) and end-tidal pCO2 (EtCO2) are of clinical interest in assessing cerebrovascular reserve capacity. Linear finite-impulse-response modelling is applied to ABP, EtCO2 and CBF velocity (CBFV, from transcranial Doppler measurements), which allows the CBFV response to ideal step changes in EtCO2 to be estimated from clinical data showing more sluggish, and additional random variations. The confounding effects of ABP changes provoked by hypercapnia on the CBFV are also corrected for. Data from 56 patients suffering from stenosis of the carotid arteries (with normal or diminished cerebrovascular reactivity to EtCO2 changes--CVRCO2) were analysed. The results show the expected significant differences (p < 0.05) between EtCO2 steps up and down, the significant contribution from ABP variation, and also differences in the dynamic responses of patients with reduced CVRCO2 (p < 0.01 after 10 s). For the latter the CBFV response appears exhausted after about 15 s, whereas for normals CBFV continues to increase. While dispersion of individual step responses remains large, the method gives encouraging results for the non-invasive study of compromised haemodynamics in different patient groups.

Aged↗
PubMed2000

Transcranial Doppler-directed Dextran-40 therapy is a cost-effective method of preventing carotid thrombosis after carotid endarterectomy.

OBJECTIVES: perioperative stroke reduces the clinical effectiveness of carotid endarterectomy (CEA). Postoperative thrombotic stroke may be reduced in incidence by the use of transcranial Doppler-directed Dextran-40 therapy. This programme requires the purchase of additional equipment and employment of more staff. This study examined whether this additional financial outlay was cost-effective in terms of saving expenditure by preventing postoperative thrombotic stroke. MATERIALS AND METHODS: data was collected prospectively on a series of 600 consecutive CEAs. The costs of the monitoring programme were analysed over 1- and 5-year periods. Formulae were derived allowing other units to calculate whether this technique will be cost-effective for them. RESULTS: after the introduction of TCD monitoring the postoperative thrombotic stroke rate fell from 2.7% to 0% (8 strokes prevented). Our local unit cost for the treatment of stroke was 25,702 pounds. After allowing for the additional costs of the monitoring programme, we calculate that postoperative TCD has saved 171,393 pounds. CONCLUSIONS: postoperative TCD monitoring is a clinically effective and also cost-effective method of reducing the stroke rate associated with CEA. For units performing more than 50 CEAs per year who experience occasional postoperative carotid thrombosis, its introduction should be considered.

Aged↗
PubMed2000

The Pruitt-Inahara shunt maintains mean middle cerebral artery velocities within 10% of preoperative values during carotid endarterectomy.

OBJECTIVE: The purpose of this study was to assess the ability of the Pruitt-Inahara shunt to maintain adequate middle cerebral artery velocities during carotid endarterectomy. STUDY DESIGN: Prospectively collected data recorded during 548 carotid endarterectomies performed at a single university hospital were analyzed to look at changes in cerebral blood flow velocities at different stages during the procedure. Parallel data relating to blood pressure and end-tidal carbon dioxide were also examined. RESULTS: During the first carotid artery cross clamp, middle cerebral artery velocity fell by 42%. A total of 169 patients (31%) had velocities that fell below 15 cm/s (electrical activity in the brain becomes altered below this level). After shunt insertion, only 2% of patients had middle cerebral artery velocities less than 15 cm/s. In only one patient was the velocity less than 10 cm/s. Increased systolic or diastolic blood pressure raised flow through the shunt significantly (P =.001). When two criteria used for selective shunt use were compared, only a moderate correlation was found between absolute middle cerebral artery velocity after carotid cross clamping and percentage change in middle cerebral artery velocity relative to preclamp values. CONCLUSIONS: The Pruitt-Inahara shunt is able to maintain adequate middle cerebral artery velocity in 98% of patients undergoing carotid endarterectomy. Alterations in blood pressure can significantly affect flow through the shunt.

Blood Flow Velocity↗
PubMed2000

Reducing the risk of carotid surgery: a 7-year audit of the role of monitoring and quality control assessment.

BACKGROUND AND PURPOSE: The current risk of stroke after carotid endarterectomy may be worse than reported in the international trials. Because studies have suggested that most operative strokes follow surgeon error, the aim of the current study was to audit the impact of introducing a strategy of perioperative monitoring and quality control assessment on outcome. METHODS: A total of 500 patients underwent carotid endarterectomy with intraoperative transcranial Doppler scan monitoring, completion angioscopy, and 3 hours of postoperative transcranial Doppler scan monitoring. The last of these guided selective dextran therapy in patients with high rates of postoperative embolization, which in previous series has been shown to be highly predictive of progression to thromboembolic stroke. RESULTS: Intimal flaps were repaired in 3% of patients and luminal thrombus removed in 4% of patients. The rate of intraoperative stroke was 0.2%. A total of 313 patients had more than one embolus detected postoperatively (96% within 2 hours of flow restoration), but only 22 patients had sustained embolization requiring dextran. Embolization ceased in all but one patient receiving dextran, although the dose had to be increased in seven patients (36%). One patient was unable to receive adequate dextran therapy because of severe cardiac failure. Overall, the 30-day death/stroke rate was 2.2%, no patient had a perioperative stroke because of carotid thrombosis, and the rate of ipsilateral embolic stroke was 0.8%. Most complications resulted from cardiac pathology or intracranial hemorrhage. CONCLUSIONS: A program of monitoring and quality control assessment has been associated with a 60% decrease in the operative risk in comparison with that observed before implementation of the protocol.

Clinical Protocols↗