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Biomedical subjects

A R Naylor

Publications and source records attributed to A R Naylor.

At least 109 records · Page 6Linked to original sources
PubMed1998

Can cerebrovascular reactivity be assessed without measuring blood pressure in patients with carotid artery disease? .

BACKGROUND AND PURPOSE: Conventional methods of assessing cerebrovascular reactivity (CVR) omit the influence of blood pressure (BP). This study demonstrates the significant influence of BP during the assessment of CVR in patients with carotid artery disease. METHODS: In 56 subjects the CVR was bilaterally assessed by measurement of cerebral blood flow velocity change in response to inhalation of 5% CO2 in air while BP was continuously monitored. Three methods of calculating the CVR were used: the conventional ratio between relative cerebral blood flow velocity and end-tidal CO2, simple linear regression, and multiple linear regression analysis (MLRA). The clinical significance of the difference in CVR indices was evaluated. The Bland-Altman test was applied to quantify the comparability and bias between measurements. The magnitude and significance of a change in BP during the CVR assessment were calculated in conjunction with an estimate of the velocity change attributed to the BP. The statistical significance of the data segment length on the variability and magnitude of the CVR index was computed. RESULTS: The value of the CVR index was reduced by 20% and 6% in comparison to the conventional ratio approach when MLRA and linear regression were applied, respectively. With the use of MLRA, in 96% of cases the value of the BP coefficient was statistically significant, and in four patients the increase in velocity was primarily attributed to the increase in BP. CONCLUSIONS: The influence of BP is significant and requires consideration when the CVR index is calculated in patients with carotid artery disease.

Aged↗
PubMed1998

A comparison of four methods for distinguishing Doppler signals from gaseous and particulate emboli.

BACKGROUND AND PURPOSE: Many reports in the medical literature have proposed methods of differentiating between gaseous and particulate emboli detected with the use of transcranial Doppler ultrasound. The purpose of this study was to compare the previously published methods with our own sample volume length (SVL) parameter to assess the accuracy of each method in classifying emboli. METHODS: A pure source of gaseous and particulate emboli was obtained from in vitro and in vivo studies, respectively, and recorded onto digital audiotape for off-line analysis. In total, 100 gaseous emboli and 215 particulate emboli were analyzed to measure four embolic parameters, namely, embolic duration, embolic velocity, relative signal intensity increase (measured embolic power [MEP]), and SVL of the embolic signal (= Duration x Velocity). Receiver operator characteristic analysis was used to assess the optimum threshold for each parameter to differentiate between particulate and gaseous emboli, and levels of sensitivity and specificity were calculated. RESULTS: Embolic duration and velocity produced the poorest levels of sensitivity and specificity compared with the MEP and SVL parameters. The optimum thresholds for embolic duration and velocity were 35 ms and 1 m/s, respectively, which produced a sensitivity (specificity) of 85.1% (87%) and 87% (67%), respectively. The optimum MEP and SVL thresholds were 30 dB and 12.8 mm, respectively, which produced a sensitivity (specificity) of 86.5% (95%) and 93% (97%), respectively. The SVL and MEP parameters were compared statistically (chi 2) at chosen specificity values of 90%, 95%, 97%, 99%, and 100%, which showed that the SVL sensitivities were statistically greater than MEP sensitivities (P < 0.01). CONCLUSIONS: SVL is the best parameter for differentiating between gaseous and particulate emboli but needs to be calculated with the use of a high-temporal-resolution spectral analyzer to measure embolic duration and velocity.

Diagnosis, Differential↗
PubMed1998

A prospective randomised trial of four-layer versus short stretch compression bandages for the treatment of venous leg ulcers.

This trial was undertaken to examine the safety and efficacy of four-layer compared with short stretch compression bandages for the treatment of venous leg ulcers within the confines of a prospective, randomised, ethically approved trial. Fifty-three patients were recruited from a dedicated venous ulcer assessment clinic and their individual ulcerated limbs were randomised to receive either a four-layer bandage (FLB)(n = 32) or a short stretch bandage (SSB)(n = 32). The endpoint was a completely healed ulcer. However, if after 12 weeks of compression therapy no healing had been achieved, that limb was withdrawn from the study and deemed to have failed to heal with the prescribed bandage. Leg volume was measured using the multiple disc model at the first bandaging visit, 4 weeks later, and on ulcer healing. Complications arising during the study were recorded. Data from all limbs were analysed on an intention to treat basis; thus the three limbs not completing the protocol were included in the analysis. Of the 53 patients, 50 completed the protocol. At 1 year the healing rate was FLB 55% and SSB 57% (chi 2 = 0.0, df = 1, P = 1.0). Limbs in the FLB arm of the study sustained one minor complication, whereas SSB limbs sustained four significant complications. Leg volumes reduced significantly after 4 weeks of compression, but subsequent volume changes were insignificant. Ulcer healing rates were not influenced by the presence of deep venous reflux, post-thrombotic deep vein changes nor by ulcer duration. Although larger ulcers took longer to heal, the overall healing rates for large (> 10 cm2) and small (10 cm2 or less) ulcers were comparable. Four-layer and short stretch bandages were equally efficacious in healing venous ulcers independent of pattern of venous reflux, ulcer area or duration. FLB limbs sustained fewer complications than SSB.

Adult↗
PubMed1997

Signals from dual gated TCD systems: curious observations and possible explanations.

Dual gated transcranial Doppler (TCD) systems have the potential to distinguish definitively embolic events in the cerebral circulation from artefact. While developing such a system, three curious observations were made and are the subject of this article. The first was that the velocity of propagation of an embolus in an artery as calculated from the ultrasonic Doppler shift was, in many cases, dramatically different from the velocity calculated using a time of flight method. The second observation was that the durations of embolic signals measured in two gates were often very different, despite the received gates being identical in length. The third observation was that some emboli detected in the deeper gate did not appear in the more superficial gate, and, more surprisingly (as has recently been reported by another group), some emboli that had not previously appeared in the deeper gate appeared in the more superficial gate. It is hypothesised that all of these effects can be explained in terms of the geometry of the middle cerebral artery in relation to the interrogating ultrasound beam. None of these effects should detract from the usefulness of TCD, but will need to be widely appreciated if dual gated measurements of cerebral emboli are to be interpreted correctly.

Cerebrovascular Circulation↗
PubMed1997

Analysis of the frequency modulation present in Doppler ultrasound signals may allow differentiation between particulate and gaseous cerebral emboli.

The purpose of this study was to investigate the incidence of frequency modulation in Doppler signals from cerebral emboli and to seek possible explanations for its occurrence. Signals from 200 particulate emboli and 200 presumed gaseous emboli were studies. The Doppler signals were visualised in the time domain and were classified into three main types. Type I signals contained no modulation, type II signals showed gradual frequency changes and type III showed a rapid change evident in only a small percentage of the entire signal. Type I signals were observed from 71.5% of particulate emboli but only 19% of gaseous emboli (X(2)) = 111, p < 0.001). Type II signals were found in 28.5% of particulate emboli and 38% of gaseous emboli (X(2)) = 4.06, p < 0.05). The most surprising and significant finding was that 43% of gaseous embolic signals were categorised as type III signals compared with 0% of signals from particulate emboli (X(2)) = 109, p < 0.001). The finding that known particulate emboli appear never to produce rapid frequency modulation may provide a basis for differentiating between gaseous and particulate emboli.

Cerebral Arteries↗
PubMed1997

Prevention of postoperative thrombotic stroke after carotid endarterectomy: the role of transcranial Doppler ultrasound.

PURPOSE: To determine the incidence of particulate embolization after carotid endarterectomy (CEA), the effect of dextran-40 infusion in patients with sustained postoperative embolization, and the impact of transcranial Doppler (TCD) monitoring plus adjuvant dextran therapy on the rate of postoperative carotid thrombosis. METHODS: Prospective study in 100 patients who underwent CEA with 6-hour postoperative monitoring using a TCD that was modified to allow automatic, intermittent recording from the ipsilateral middle cerebral artery waveform (10 minute sample every 30 minutes). An incremental dextran-40 infusion was commenced if 25 or more emboli were detected in any 10-minute period. RESULTS: Overall, 48% of patients had one or more emboli detected in the postoperative period, particularly in the first 2 hours. However, sustained embolization that required Dextran therapy developed in only five patients. In each case, the rate of embolization rapidly diminished. CONCLUSIONS: A small proportion of patients have sustained embolization after CEA, which in previous studies has been shown to be highly predictive of thrombotic stroke. Intervention with dextran reduced and subsequently stopped all the emboli in those in whom it was used and contributed to a 0% perioperative morbidity and mortality rate in this series.

Adult↗
PubMed1997

Microembolization during endovascular and conventional aneurysm repair.

PURPOSE: Endovascular aneurysm repair has been advocated as a "minimally invasive" alternative to conventional aneurysm surgery. However, because of manipulation within the aneurysm sac, endovascular techniques may result in massive microembolization. METHODS: In this study lower limb microemboli were quantified in 29 patients undergoing conventional (11 straight and 7 bifurcated grafts) and endovascular aneurysm repair (8 aortoiliac, 1 straight, and 2 bifurcated grafts) by insonation of the superficial femoral artery with a 2 MHz Doppler probe. Emboli were detected as high-intensity, short-duration signals on the background Doppler trace. Differentiation of gaseous emboli from particulate emboli was achieved by calculation of the sample volume length (emboli velocity x duration = sample volume length) for each embolus (N = 4927). Previous experiments had determined that a sample volume length < 1.4 cm represented particulate embolization. RESULTS: The number of gaseous, particulate, and total emboli were significantly greater in the endovascular group compared with the conventional group (p < 0.05). CONCLUSIONS: These data demonstrate that peripheral microembolization is significantly higher during endovascular aneurysm repair than during conventional surgery. Methods to reduce embolization must be developed before endovascular aortic surgery is widely adopted.

Aged↗
PubMed1997

Ultrasound-based quantification of emboli during conventional and endovascular aneurysm repair.

PURPOSE: To differentiate and quantify the type and number of lower limb emboli occurring during endovascular aneurysm repair, as compared to conventional surgery. METHODS: Thirty-eight patients underwent elective infrarenal aneurysm repair using a conventional surgical approach in 18 and an endovascular procedure in 20. Emboli were detected using a Doppler ultrasound system with a 2-MHz transducer interrogating the mid superficial femoral artery. Lower limb emboli were differentiated as particulate or gaseous based on the physical distance traversed by the embolic signal. RESULTS: Significantly more particulate (median 108 versus 59, p = 0.015) and gaseous (134 versus 46, p = 0.008) emboli were detected during endovascular aneurysm repair as compared to conventional surgery. Clinically, no case of massive microembolization occurred in either group, but one patient in the conventional group required a femoral embolectomy, and three patients undergoing endovascular repair developed self-limiting trash feet postoperatively. In patients undergoing endovascular aortomonoiliac aneurysm repair, there was only a poor correlation between the number of particulate emboli and either procedural duration or operator experience. CONCLUSIONS: The apparent lack of a relationship between particulate embolization and operative time or technical experience suggests that manipulation of endoluminal devices within the aneurysm sac may not be the sole determinant of intraprocedural embolization. Other as yet undetermined factors may predict patients at high risk for massive embolization.

Aged↗
PubMed1997

Single-visit venous ulcer assessment clinic: the first year.

BACKGROUND: Venous ulceration is a significant clinical problem to both clinicians and patients. To optimize the management of patients with ulcers a single-visit, dedicated venous ulcer assessment clinic was set up. METHODS: All patients referred to the clinic during the first year were recorded prospectively. Each patient was assessed clinically and with colour-coded venous and, where indicated, arterial duplex scanning. Ulcers were classified as venous, arterial, mixed or non-vascular on a basis of ankle:brachial pressure indices and venous duplex scanning. RESULTS: Eighty-eight patients (104 limbs with ulcers) were assessed. Seventy-nine per cent of ulcers were venous, 2 per cent arterial, 12 per cent mixed and 7 per cent non-vascular. Of the 95 limbs with demonstrable venous reflux, reflux was confined to the superficial system in 57 per cent, the deep system in 6 per cent and was combined in 37 per cent of limbs. Of the 22 patients who reported previous deep vein thrombosis, nine had normal deep vein function. Some 38 per cent of limbs with no history of previous thrombosis had abnormal deep vein function. CONCLUSION: In this clinic 14 per cent of leg ulcers had a significant arterial component and over half of venous ulcers may benefit from superficial venous surgery. In many ulcerated limbs, clinical assessment alone is inadequate to detect superficial reflux or previous deep vein thrombosis.

Adult↗
PubMed1996

Aggressive limb salvage using tibio-pedal bypass grafting with free tissue transfer in a diabetic patient.

A 63-year-old man presented with intermittent claudication, diabetes, and an ischaemic heel ulcer. After control of infection, the os calcis was left exposed. An aggressive combined infra-inguinal revascularization and reconstruction procedure involving free-tissue transfer resulted in rapid wound healing with independent walking by day 26. Recent improvements in surgical techniques mean that this approach should be considered in selected patients.

Angiography↗
PubMed1996

Surveillance imaging of the operated artery does not alter clinical outcome following carotid endarterectomy.

Clinical outcome was studied in 243 patients undergoing 260 carotid endarterectomies; 166 of these patients underwent serial postoperative surveillance imaging. Including perioperative events, cumulative freedom from ipsilateral stroke was 86 and 82 per cent at 5 and 10 years respectively; the mean incidence of ipsilateral stroke was 1.8 per cent per annum. Twenty patients (8 per cent) suffered cerebral ischaemic events in the hemisphere of the operated side during follow-up: eight transient ischaemic attacks (TIA) and 12 strokes (only two preceded by TIA). Two symptomatic patients were found to have occluded the operated artery but the remainder had no evidence of significant recurrent disease. Cumulative freedom from occlusion or severe (greater than 70 per cent) recurrent stenosis was 87 and 78 per cent at 5 and 10 years respectively; the mean incidence of recurrence of significant disease was 2.2 per cent per annum. No revisional surgery was performed on the operated arteries. In its current format, neither clinical nor surveillance imaging could have prevented any of the strokes observed during follow-up.

Angiography, Digital Subtraction↗
PubMed1996

Prospective audit of discharge summary errors.

During an 8-month interval of prospective audit, 63 of 637 (10 per cent) vascular discharge summaries were found to contain 94 errors. These comprised 11 (12 per cent) general errors, 21 (22 per cent) diagnostic errors, 19 (20 per cent) operative data errors, 19 (20 per cent) cases of incorrect clinical text information, 14 (15 per cent) missed complications and 10 (11 per cent) concerning follow-up arrangements. Overall, 2 per cent of consultant discharge summaries contained errors compared with 7 per cent for the senior registrar, 10 per cent for registrars and 17 per cent for senior house officers. Given that the majority of discharge summaries are currently prepared by junior staff, this study suggests that verification of the accuracy of clinical and management data should be an essential component of departmental audit meetings.

Diagnostic Errors↗
PubMed1996

Colour-coded duplex imaging can safely replace diagnostic arteriography in patients with lower-limb arterial disease.

The purpose of this study was to review the outcome of adopting colour-coded duplex ultrasonography as the primary imaging modality in patients with symptomatic lower-limb arterial disease. Over a 12-month period 467 consecutive lower-limb duplex scans were performed of which 437 (94 per cent) were technically adequate. Of the 467 limbs, 184 (39 per cent) were managed conservatively, 230 (49 per cent) were referred for percutaneous transluminal angioplasty (PTA), 41 (9 per cent) underwent reconstructive surgery and 12 (3 per cent) required diagnostic arteriography. In patients referred for PTA there were only 22 (10 per cent) unexpected findings; there was agreement about superficial femoral artery occlusion length in 95 (89 per cent) of 107 limbs and about the presence or absence of a superficial femoral artery stump in 91 (85 per cent) of 107 cases. In patients referred for surgery there were no unexpected findings. Colour-coded duplex imaging can safely replace diagnostic arteriography in up to 97 per cent of lower limbs with arterial disease.

Adult↗
PubMed1996

Differentiation between emboli and artefacts using dual-gated transcranial Doppler ultrasound.

It is well documented that transcranial Doppler ultrasound has the ability to detect cerebral emboli. During intraoperative patient monitoring studies, many signals due to artefact (probe motion, patient movement or surgical manipulation) are also detected and can be difficult to distinguish from genuine embolic events. We have constructed a Doppler system that can simultaneously range-gate at two separate depths, in order to test the hypothesis that it should be possible to distinguish between emboli and artefact by comparing the signal from the two separate regions within the vessel. The classification algorithm is based on the principle that emboli propagate with blood motion (whereas artefacts do not) and thus will be detected sequentially at different depths along the insonated cerebral artery. One hundred thirty-eight (presumed) embolic and 170 artefact signals were analysed. The median (interquartile range) gate separation was 10.01 mm (7.41-10.78 mm). The time delay between detection of embolic signals in the two channels was 11.04 ms (6.24-16.41 ms, but was only 0.08 ms (-0.48(-)+0.64 ms) for artefact (p < 0.0001). Dual-gated Doppler ultrasound is a conclusive and independent method that differentiates emboli from artefact. Incorporation of this system for long-term monitoring may eliminate the need for an experienced observer to be present.

Artifacts↗