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Biomedical subjects

A R Naylor

Publications and source records attributed to A R Naylor.

At least 163 records · Page 9Linked to original sources
PubMed1993

Transcranial colour coded sonography as an aid to measurement of blood flow velocity in the basal cerebral arteries.

Unlike conventional transcranial Doppler, transcranial colour coded sonography allows imaging of the basal cerebral arteries. We used this technique to determine blood flow velocities, with compensation for the angle of insonation, in the anterior and posterior cerebral circulation of 60 volunteers categorised by age (20-39, 40-59, > 60 years). Successful vessel insonation declined with increasing age: 40/40 middle cerebral arteries insonated 20-39 y, 31/40 insonated > 60 y. Peak, mean and end diastolic blood flow velocities also decreased with age in all arteries: 20-39 y middle cerebral artery mean velocity = 72 cm/s; > 60 y middle cerebral artery mean blood flow velocity = 58 cm/s; p < 0.0001. The pulsatility index increased significantly with age in the middle, posterior cerebral (P2 segment) and vertebral arteries (p < 0.05-0.005), however the resistance index increased significantly with age in all vessels (p < 0.05-0.0001).

Adult↗
PubMed1993

Selection of patients with critical limb ischaemia for femorodistal vein bypass.

The merits of an aggressive policy of distal reconstruction have been questioned by some observers. To determine the factors affecting graft patency and mortality, we analysed 78 consecutive infragenicular femorodistal vein grafts performed in 72 patients with critical limb ischaemia. The primary, primary assisted and secondary graft patency rates at 36 months were 29, 57 and 64%, respectively. The limb salvage and patient survival rates at 36 months were 67 and 74%, respectively. Univariate analysis (log-rank test) was performed to identify factors affecting graft patency, limb salvage and mortality at 1 month (perioperative) and 1 year. Independent variables of age, sex, diabetes, presentation, level of anastomosis and vein technique (reversed or in situ) did not affect graft patency. The ankle systolic pressure did not predict graft patency but was an independent variable affecting mortality (p = 0.047), as did diabetes (p = 0.019). These results show that excellent limb salvage can be successfully achieved in severely ischaemic patients by adopting an aggressive approach to femorodistal bypass, and that age, gender and poor medical condition are not contraindications to femorodistal bypass. The difference between the primary and primary assisted patency rates in this series is dramatic and reflects the impact of a vein graft surveillance programme in preventing graft occlusion.

Adult↗
PubMed1993

Immediate effects of carotid clamp release on middle cerebral artery blood flow velocity during carotid endarterectomy.

Transcranial Doppler ultrasound was employed in 44 patients undergoing carotid endarterectomy in order to identify factors associated with the greatest increases in middle cerebral artery blood flow velocity (MCAV) immediately after carotid clamp release and restoration of flow. Previous reports have suggested that such increases might reflect post-ischemic hyperaemia. Overall, the median increase in MCAV on restoration of flow [58 cm/s (95% Cl 44-68)] was greater than the median decrease in MCAV after initial carotid clamping [36 cm/s (95% Cl 26-43), p < 0.0001]. However, the immediate increase in MCAV tended to be transient and, in one patient, may have represented a hyperaemic response to a haemodynamically induced intraoperative neurological deficit. There was no association between the magnitude of MCAV increase and clinical presentation, degree of carotid stenosis, computed tomography scan findings, type of anaesthesia, nor the presence or absence of impaired cerebral vascular reserve, nor the occurrence of intraoperative air embolisation. The greatest increases in MCAV on clamp release were observed in patients with the greatest decreases in MCAV at clamping and those with the lowest internal carotid artery stump pressures. The most likely explanation for the findings is that they represent a transient hyperaemic response to carotid occlusion. It remains unclear whether this phenomenon is mediated by some degree of ischaemic injury or simply by the effect of a sudden surge of blood through low resistance arterioles that have dilated in order to maintain the collateral circulation during carotid clamping.

Blood Flow Velocity↗
PubMed1993

Patterns of vascular pathology in acute, first-ever cerebral infarction.

This was a preliminary study to see whether patterns of vascular pathology correlated with a simple clinical classification of acute cerebral infarction. Thirty-two patients with acute, first-ever hemispheric cerebral infarction were prospectively studied clinically together with an extra- and transcranial Doppler ultrasound. All 14 patients with the triad of ipsilateral motor/sensory deficit, homonymous hemianopia and higher cortical dysfunction (Total Anterior Circulation Infarction, [TACI]) had occlusion of the symptomatic middle cerebral artery and/or internal carotid artery, or a severe middle cerebral artery stenosis. Three patients with lacunar infarction had no evidence of major vessel occlusion. Eleven of thirteen patients with Partial Anterior Circulation, Infarction (PACI) I (i.e. only one or two clinical features of the TACI triad) had patent symptomatic major vessels, with indirect evidence to suggest distal branch occlusion(s) of the middle cerebral artery in six. The remaining two PACI patients had major vessel occlusions. Two patients were not clinically classifiable, but both had significant vascular pathology on ultrasound. The findings of this preliminary study therefore suggest that a simple clinical classification was generally capable of predicting patterns of vascular pathology in patients with acute cerebral infarction, which could have implications for the selection of patients for clinical trials of thrombolytic therapy.

Acute Disease↗
PubMed1993

An audit of trends and current practice of carotid endarterectomy in Edinburgh (1975-1990).

Changes in the patient population and trends in management were studied for 260 consecutive carotid endarterectomies performed during the periods 1975-1982 and 1983-1990. A 43% increase was observed in the number of operations (from 107 to 153), an 81% increase taking into account patients randomized to medical treatment in the European Carotid Surgery Trial. There were significant reductions in patients continuing to smoke (79 to 60%, P = 0.001), in those with systolic hypertension (21 to 11%, P = 0.018) and diastolic hypertension (26 to 12%, P = 0.002), and in those with asymptomatic carotid lesions (8 to 2%, P = 0.031). There were significant increases in the proportion of patients with strokes presenting with a residual neurological deficit (40 to 66%, P = 0.024), and in those with ocular symptoms (30 to 50%, P = 0.001) and with stenoses greater than 50% (58 to 71%, P = 0.018). This study suggests a trend for a higher risk population with more severe carotid disease. In the light of results of clinical trials, further evolution of patient selection is likely to occur and should be taken into account when evaluating the risk of carotid endarterectomy.

Adult↗
PubMed1993

The management of cardiac trauma by general surgeons in non-cardiothoracic units.

Cardiac trauma requiring immediate surgical intervention is usually thought of as a rare event. However, our recent experience at Leicester Royal Infirmary suggests that this clinical situation is on the increase, and has highlighted potential problems in the management of these patients. It is essential that all units that may have to deal with these patients have the necessary facilities and equipment to perform an emergency thoracotomy in the Accident and Emergency department, and that the medical and nursing staff involved have been properly trained to deal with these life-threatening emergencies.

Adolescent↗
PubMed1992

Monitoring and cerebral protection during carotid endarterectomy.

Two recently published multicentre trials have confirmed the overall benefit of carotid endarterectomy in symptomatic patients with severe carotid artery disease. The key to improving further the long-term advantages of carotid endarterectomy, however, remains the continued reduction of the initial operative risk. While the principal responsibility for this continues to be borne by the surgeon, specifically in reducing technical error, the time is perhaps approaching when he or she might also be able to apply some of the recent advances in cerebrovascular research to reduce operative morbidity still further in the future. This article summarizes the aetiology and pathophysiology of operation-related neurological deficits and reviews current approaches towards intraoperative monitoring, cerebral protection and assessment of quality control.

Brain Ischemia↗
PubMed1992

In vivo effect of calcitonin gene related peptide on middle cerebral artery blood flow velocity in humans.

A double blind, placebo controlled, escalating dose study was undertaken in five healthy, conscious volunteers to investigate the effects of human synthetic alpha calcitonin gene-related peptide (CGRP) on middle cerebral artery (MCA) blood flow velocity using transcranial Doppler sonography. During placebo infusion, there was no significant change in any of the parameters studied. During CGRP infusion, all subjects showed flushing of the face and neck. Infusion of CGRP caused a significant increase in arterial pulse pressure and heart rate and a fall in diastolic and mean arterial blood pressure when compared to baseline. Peak and mean MCA velocity did not change significantly. There was a significant increase in pulsatility index though interpretation of this was confounded by the central systemic effects of CGRP. The observed haemodynamic changes may be explained by a prompt sympathetic nervous system response in order to maintain mean arterial blood pressure. Our data suggest that if cerebral vasodilatation had occurred, it was not associated with increased blood flow as an increase in MCA velocity might have been expected. An alternative explanation is that, at the doses employed, CGRP did not cause dilatation of normal cerebral vessels in healthy subjects. This does not however exclude the fact that CGRP may cause dilatation of a spastic artery as seen in cerebral vasospasm following subarachnoid haemorrhage.

Journal Article↗
PubMed1991

Transcranial Doppler monitoring during carotid endarterectomy.

Transcranial Doppler monitoring of the middle cerebral artery blood flow velocity was used as an adjunct to routine methods of cerebral monitoring in a prospective study of 30 consecutive patients undergoing carotid endarterectomy to investigate whether transcranial Doppler monitoring provided information influencing operative technique. Application of carotid clamps caused a significant fall in middle cerebral artery velocity and there was a linear relationship between middle cerebral artery velocity and internal carotid artery stump pressure. Assuming a stump pressure of less than 50 mmHg to be an indication for shunting, this would correspond to a systolic middle cerebral artery velocity of less than 42 cm/s and a mean velocity of less than 30 cm/s. Transcranial Doppler monitoring immediately identified problems with shunt function and demonstrated a higher frequency of intraoperative embolization than had been anticipated, particularly after shunt insertion and final restoration of flow. With revision of operative technique this phenomenon is rarely encountered now. Two of the 30 patients exhibited a minor neurological deficit on recovery of consciousness, and transcranial Doppler monitoring was able to identify the probable underlying cause in both cases. Unnecessary and potentially hazardous re-exploration was avoided. In the absence of transcranial Doppler monitoring the neurological deficit in one of the patients might have been much worse.

Blood Flow Velocity↗
PubMed1991

Parametric imaging of cerebral vascular reserve. 2. Reproducibility, response to CO2 and correlation with middle cerebral artery velocities.

We report the reproducibility and response to change in end-tidal CO2 of a new method of quantifying regional mean cerebral transit time (MCTT) compared with the reproducibility and CO2 reactivity of middle cerebral artery (MCA) blood flow velocities measured using transcranial Doppler ultrasound. Within the range of end-tidal CO2 which could be achieved in conscious subjects breathing spontaneously, hemispheric MCTT, peak MCA velocity and mean MCA velocity showed a linear relationship with end-tidal CO2. After correction to a standardised end-tidal CO2, the coefficients of variation were 5.7% for hemispheric MCTT, 6.3% for peak MCA velocity and 6.8% for mean MCA velocity. Under the conditions of this study, MCA blood flow velocity was proportional to the reciprocal of MCTT, which in turn represents the ratio of blood flow to blood volume. Although the two methods appear to provide similar information, measurement of MCTT is quicker to perform, is less observer-dependent, provides regional information, uses conventional equipment present in most nuclear medicine departments and is less subject to problems associated with patient movement.

Adult↗
PubMed1991

Risk factors for intra-operative neurological deficit during carotid endarterectomy.

Although embolism is considered to be the major cause of intra-operative neurological deficit (IOND) during carotid endarterectomy, the possibility that patients may vary in susceptibility to ischaemic damage following minor embolisation or falls in cerebral perfusion pressure is rarely considered. A prospective study was undertaken in 60 consecutive patients undergoing carotid endarterectomy to identify risk factors for IOND. The hypothesis was that patients with impaired cerebral vascular reserve (CVR) may be more vulnerable to intra-operative emboli or falls in cerebral perfusion pressure than normal subjects. Recent work using Positron Emission Tomography has indicated that the best index of CVR is the ratio of cerebral blood flow to cerebral blood volume, which is another expression for the reciprocal of mean cerebral transit time (MCTT). In this study, a new isotopic method of quantifying MCTT was used to identify patients with impaired CVR. Six patients (10%) recovered from anaesthesia with an IOND, only one of which was disabling. Significant risk factors for IOND were: (i) age over 65 years (Odds Ratio 13.0 (95%CI 1.4-121), p = 0.013); (ii) a residual neurological deficit prior to operation (Odds Ratio 7.0 (95%CE 1.1-43), p = 0.038); (iii) complex plaque morphology (Odds Ratio 6.4 (95%CI 1.06-34), p = 0.046); and (iv) the combination of impaired CVR and a CT scan infarct in the symptomatic hemisphere (Odds Ratio 9.8 (95%CI 1.5-62), p = 0.026). These observations suggest that certain risk factors for IOND can be identified preoperatively and this may enable a more discriminating approach to patient selection for operation and a more critical evaluation of operative technique and methods for intra-operative protection and monitoring in the future.

Age Factors↗
PubMed1990

T tube intubation in the management of seriously ill patients with oesophagopleural fistulae.

Ten patients referred late with oesophagopleural fistulae were managed by T tube intubation of the oesophageal defect. Seven survived and six had radiographic evidence of closure of the defect. One patient who removed his T tube early was discharged to convalesce with a small oesophagocutaneous fistula. Three patients died as a consequence of pre-existing renal failure, upper gastrointestinal haemorrhage and adult respiratory distress syndrome. Patients presenting late with multisystem complications and ongoing sepsis secondary to oesophagopleural fistulae pose a major management problem. Our preliminary results suggest that T tube intubation offers a potential alternative to major surgical intervention, when more conservative measures have failed.

Acute Kidney Injury↗
PubMed1990

Aortoiliac endarterectomy: an 11-year review.

Fifty-seven patients underwent aortoiliac endarterectomy over an 11-year period, the majority (86 per cent) for disabling claudication. No patient died within 30 days of surgery, but nine patients suffered significant complications. The cumulative survival rate was 98 per cent at 1 year, and was 94 and 78 per cent at 5 and 10 years respectively. Cumulative operated segment patency rates were 92 per cent at 5 years and 68 per cent at 10 years. There was no significant difference in survival rates between patients who smoked after surgery and those who did not, but smokers had significantly worse rates for cumulative patency, limb failure and symptom status than non-smokers. Twenty-seven patients developed worsening symptoms during follow-up and 24 patients required secondary vascular intervention. Fourteen patients subsequently required aortofemoral bypass and the largest single cause of operated segment failure was recurrent disease in the external iliac artery. Our evidence suggests that, while aortoiliac endarterectomy should be considered in young patients with localized disease not involving the external iliac artery, those who do not fit these criteria should be considered for primary aortofemoral bypass. Regardless of the choice of operation, the chance of success is jeopardized if the patient continues to smoke.

Adult↗