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Biomedical subjects

M M Brown

Publications and source records attributed to M M Brown.

At least 109 records · Page 6Linked to original sources
PubMed1994

Carotid angioplasty. Detection of embolic signals during and after the procedure.

BACKGROUND AND PURPOSE: Carotid angioplasty may offer an effective treatment for carotid stenosis, but there has been concern about the incidence and clinical consequences of distal embolization. Transcranial Doppler monitoring in carotid endarterectomy has demonstrated embolic signals during this procedure. We used this technique in patients undergoing carotid angioplasty. METHODS: Transcranial Doppler ultrasound was used to monitor for embolic signals in the ipsilateral middle cerebral artery before and during 10 technically successful carotid angioplasties and at various standardized times in the following month. RESULTS: In the month before angioplasty asymptomatic embolic signals were detected in 3 of 10 patients. During angioplasty multiple embolic signals were detected immediately after balloon inflation in 9 of 10 subjects. A minor ipsilateral cerebral ischemic event occurred in 1 of these 9, but the other 8 were asymptomatic. Embolic signals were common immediately after the procedure and intra-arterial femoral catheter removal (8 of 10 subjects) but thereafter became less frequent and were present in 1 of 5 at 4 hours, 2 of 10 at 48 hours, 1 of 6 at 7 days, and 1 of 10 at 1 month. CONCLUSIONS: Embolization at the time of carotid angioplasty is very common but usually asymptomatic; monitoring by means of Doppler ultrasound will allow the effectiveness of measures to reduce this embolization to be studied. Late embolization occurs in a minority of patients and may account for the small but significant risk of delayed stroke. Doppler monitoring may allow identification of patients at risk and assessment of the effectiveness of prophylactic therapy.

Aged↗
PubMed1994

The effect of velocity on the appearance of embolic signals studied in transcranial Doppler models.

BACKGROUND AND PURPOSE: Transcranial Doppler ultrasound can be used to detect circulating cerebral emboli. Recent studies have demonstrated that embolus size is significantly related to both the relative intensity increase and duration of an embolic signal. This may allow information about embolus size to be obtained by analysis of Doppler embolic signals. However, theoretically duration will be inversely related to velocity, and therefore velocity may need to be accounted for if information on embolus size is to be derived from the duration of Doppler embolic signals. METHODS: The relation between velocity and both relative intensity increase and duration of embolic signal was investigated in an in vitro flow model, a sheep carotid artery model, and in patients with prosthetic heart valves. The same standard transcranial Doppler ultrasound machine was used for all studies. Embolic signals resulting from 99 glass microspheres (size, 210 to 250 microns) were studied in the in vitro model, as were those from 64 glass microspheres (size, 105 to 150 microns) in the sheep model. Embolic signals recorded from the six middle cerebral arteries of three patients with prosthetic cardiac valves were also studied. RESULTS: There was a significant (P < .001) inverse relation between velocity and duration of high-intensity signal (in vitro model, r = -.82; sheep model, r = -.43); the exact relations were described using best-fit equations. Correlation coefficients for this relation in patients varied between -.30 and -.55. There was also an unexpected significant positive relation between velocity and intensity in the sheep model (r = .44, P < .001) but not in the in vitro model (P > .05). This relation was also seen in some, but not all, patients. CONCLUSIONS: When the duration of embolic signals is used to provide information about the relative size of an embolus, the velocity of the embolic signal should be taken into account. A relation between velocity and relative intensity increase was found in the sheep model and in some patient recordings. It is suggested this relation may result from greater power being supplied to emboli traveling at higher velocities in the center of the vessel; this may occur under certain recording conditions.

Animals↗
PubMed1994

Differential effect of three cyclooxygenase inhibitors on human cerebral blood flow velocity and carbon dioxide reactivity.

BACKGROUND AND PURPOSE: Prostaglandins are believed to play an important role in maintenance of cerebral blood flow and possibly in the vasodilatory response to carbon dioxide. Therefore, the nonsteroidal anti-inflammatory drugs and aspirin, which inhibit cyclooxygenase, might be expected to reduce cerebral blood flow and the response to hypercapnia. This could induce cerebral ischemia in patients with a hemodynamically critical circulation. It would also interfere with the measurement of cerebrovascular reserve using carbon dioxide. METHODS: The effect of a single dose of indomethacin and of two other cyclooxygenase inhibitors (aspirin and sulindac) on the cerebral circulation was measured using transcranial Doppler ultrasonography of the middle cerebral artery. Seven normal adults were studied in each drug group. Resting blood flow velocity and the responses to hypercapnia and to hyperventilation were measured. RESULTS: Indomethacin resulted in a fall in basal middle cerebral artery flow velocity from a mean of 48.9 cm/s to 34.0 cm/s (P < .002). It also reduced the vasoconstrictor response to hypocapnia (induced by hyperventilation) from 37.5% to 20.7% (P < .003). There was a nonsignificant reduction in the vasodilatory response to 8% carbon dioxide (mean: predrug, 87.7%; postdrug, 61.0%), with marked intersubject variability. In contrast, basal middle cerebral artery velocity and vasoconstrictor and vasodilatory responses to changes in carbon dioxide were unchanged after aspirin or sulindac administration. CONCLUSIONS: The lack of effect of aspirin on basal cerebral blood flow velocity and on vasodilatory reserve is reassuring; aspirin will not reduce cerebral blood flow or the response to a reduced perfusion pressure in patients with critically impaired cerebral hemodynamics. However, indomethacin should be avoided in such patients.

Adult↗
PubMed1994

The use of acyclovir in suspected encephalitis.

The early use of intravenous acyclovir in herpes simplex encephalitis (HSE) is essential. However, rapid diagnostic tests are not freely available. Hence, all patients with suspected encephalitis may need to be commenced on acyclovir. In our study, of 34 patients with suspected encephalitis, only two eventually had HSE confirmed, 19 had encephalitis not due to herpes simplex and in 13 a non-encephalitis illness was finally diagnosed. Guidelines for the use of acyclovir in suspected encephalitis are given aimed at minimizing the drug cost whilst still protecting all cases of presumed HSE.

Acyclovir↗
PubMed1994

Magnetic resonance neurography of the median nerve.

A magnetic resonance imaging sequence, combining fat and flow suppression with T2 weighting, has been used to produce high conspicuity images of the median nerve within the carpal tunnel. Standard maximum intensity projection techniques were then used to produce three-dimensional (3D) reconstructions of the nerve. Comparison of 3D projections with the wrist in a neutral position and wrist flexed at 45 degrees depicted changes in the shape and course of the median nerve through the carpal tunnel of normal volunteers. In some cases of carpal tunnel syndrome evidence of a localized compression was observed. A 3D image of a nerve may help in the diagnosis of peripheral neuropathy and be an aid to surgery of or near major nerves.

Adult↗
PubMed1994

Polymorphisms in the gene encoding angiotensin 1-converting enzyme and relationship to its post-translational product in cerebral infarction.

There is increasing evidence to suggest that the gene encoding angiotensin 1-converting enzyme (ACE) plays a significant part in cardiac disease risk. It is not clear if this risk is due to atherosclerotic factors in general or whether its influence is local to cardiac tissue. Previous studies have suggested that there is a genetic control of plasma ACE levels in normal subjects. We sought to see if such a relationship also existed amongst computer tomography (CT) proven cerebral infarction. Twenty-eight patients with stroke and 19 control subjects were grouped according to their ACE genotype and their plasma ACE levels were assessed. Although there is a trend for plasma levels to be associated with the variant ACE alleles there was a wide overlap. However, when compared with their respective alleles in control subjects there was no difference. We conclude that any future evaluation of stroke risk from the ACE gene will need to determine both plasma ACE level and genotype.

Adult↗
PubMed1994

Molecular approach to assessing the genetic risk of cerebral infarction: deletion polymorphism in the gene encoding angiotensin 1-converting enzyme.

Numerous factors have been reported to influence the pathogenesis of stroke. The risks arising from variations in genes between individuals have not been explored. The angiotensin 1-converting enzyme gene is a candidate gene for atherosclerotic related disease. In this work we studied the frequency of the deletion allele D and the polymorphism DD within the gene encoding angiotensin 1-converting enzyme in stroke patients compared with controls to determine if this deletion polymorphism was a potential independent risk factor for stroke. We report a study of 100 patients with cerebral infarction along with 73 normal age and sex matched controls. Personal medical histories associated with high risk factors for stroke were documented. Cholesterol and triglyceride levels for each individual were also measured. Using polymerase chain reaction techniques patients were divided into the three angiotensin 1-converting enzyme genotypes (Deletion D and Insertion I) II, ID and DD. The D/I frequency in patients with stroke (0.57/0.43) was compared with controls (0.48/0.52). This was not statistically different (P > 0.05, chi-squared test). Although strokes did occur at a younger age in those with the DD genotype compared with those with the insertion allele, the results did not approach acceptable levels of significance (II/ID) (P > 0.05, Mann-Whitney U-test). There were no differences between the three genotypes and other well accepted risk factors for stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Microscopic air embolism during cerebral angiography and strategies for its avoidance.

Cerebral angiography is associated with a risk of neurological complications and air embolism may contribute towards this risk. To test this hypothesis, transcranial doppler ultrasonography was used to monitor the presence of air emboli in the middle cerebral arteries of 7 patients undergoing cerebral angiography. Doppler signals consistent with numerous air emboli were noted during each injection of radiographic contrast. This phenomenon was studied further in sheep. Radiographic contrast medium was injected into the carotid artery while a major carotid branch was insonated transorbitally. Embolic signals similar to those seen in patients were noted. Air was introduced at two points. First, at the time of drawing up the contrast into the syringe, especially with more viscous media. Standing the media before injection resulted in a highly significant reduction of air embolism, reducing the total mean duration of emboli from 1.32 (SD 0.60) s after immediate injection to 0.04 (0.05) s after ten minutes standing for iohexol 340 mg/mL (p < 0.001). Second, air was introduced at the time of injection, possibly by the formation of cavitation bubbles under pressure. This occurred most prominently with the less viscous contrast media and with saline, and was significantly reduced by slow injection (mean duration of emboli for saline 2.85 [2.43] s with fast injection compared with 0.32 [0.37] s with slow injection, p = 0.004). Air embolism may contribute towards neurological dysfunction after angiography. Measures should be taken to reduce this by allowing contrast media to stand prior to injection, and by flushing catheters with saline injected slowly.

Adult↗
PubMed1993

Improving medical students' attitudes toward and skills with the elderly.

This study examined the effect of an experimental program in gerontology and geriatrics on the knowledge, attitudes, and interview skill behaviors of third-year medical students. Experimental group members (n = 45; controls n = 51) participated in four 90-minute group sessions that emphasized psychological, sociodemographic, and physiological aspects of aging and interpersonal communication skills. Program participants developed more positive attitudes and demonstrated more socially skilled behavior during an interview with an older adult.

Adult↗
PubMed1993

Control of postoperative bleeding in the cardiac surgery patient.

Postoperative bleeding is caused by alterations in the normal process of hemostasis or by a surgical problem. The role of platelets, coagulation proteins, and fibrinolysis in the control of postoperative bleeding is reviewed, as are preoperative and intraoperative factors that interfere with these normal processes. Current treatment of postoperative bleeding is discussed, including the use of positive end-expiratory pressure, control of hypertension, medication, and blood products.

Blood Coagulation↗
PubMed1993

A family showing no evidence of linkage between the ataxia telangiectasia gene and chromosome 11q22-23.

We have studied an inbred family in which two cousins presented with the same clinical features of ataxia telangiectasia (AT). Both patients are still ambulatory at ages 25 and 20. Cellular features of both patients are typical of AT and include increased radiosensitivity and an increased level of spontaneously occurring chromosome aberrations in peripheral blood lymphocytes. Linkage studies and haplotype analysis show no clear evidence that the gene for AT in this family is on chromosome 11q22-23. As previously reported AT families from complementation groups AB, C, and D have all shown linkage to this region of 11q22-23. Our study is of importance in suggesting additional locus heterogeneity.

Adult↗
PubMed1993

Differentiation between different pathological cerebral embolic materials using transcranial Doppler in an in vitro model.

BACKGROUND AND PURPOSE: The detection of circulating particulate cerebral emboli using transcranial Doppler ultrasonography has been recently reported. It has been suggested that this method might allow discrimination between different embolic materials; this would be very useful for selecting specific pharmacological treatment in individual patients. This study was designed to identify those parameters of the Doppler signal that might prove useful in discriminating between different types and sizes of particulate cerebral emboli. METHODS: An extracorporeal circuit filled with a saline/Tween solution and driven by a peristaltic pump was used. The tubing was placed in a skull in the position of the middle cerebral artery. Using transcranial Doppler ultrasound, flow was insonated via the transtemporal window. The following embolic materials of measured sizes (range of maximum dimension, 0.5-5.0 mm) were introduced into the circuit: thrombus (n = 20), platelet-rich aggregates (n = 15), atheromatous material (n = 20), and fat (n = 20). The Doppler signal was recorded during the passage of each embolus. Off-line analysis was performed to measure the maximum amplitude and duration of the signal. RESULTS: For all embolic materials there was a highly significant relation between embolus size and maximum amplitude of the Doppler signal. The closest correlation was obtained when the logarithm of maximum amplitude was used (for thrombi, r = 0.74; for platelet, r = 0.87; for atheroma, r = 0.46; and for fat, r = 0.68). The slope of the regression line differed for the different embolic materials and was significantly steeper for platelets than for atheroma (p < 0.01). Platelet emboli of maximum dimension < or = 1.5 mm resulted in a significantly lower maximum amplitude than similarly sized atheroma emboli (157 dB versus 206.7 dB, p < 0.01). For larger emboli (> 2 mm) there was little further increase in maximum amplitude with increases in embolus size. For all embolic materials there was a highly significant linear relation between embolus size and duration of the high-amplitude (> 150 dB) signal (for thrombi, r = 0.75; for platelet, r = 0.90; for atheroma, r = 0.77; and for fat, r = 0.86). CONCLUSIONS: Platelet emboli result in lower-amplitude signals, and therefore analysis of maximum amplitude may provide information on the type of embolic material. However, it may be difficult to determine whether a given signal is associated with a large platelet embolus or a small atheroma embolus. Duration of the high-amplitude signal will allow accurate estimation of the size of emboli, particularly where the emboli are all of the same material.

Blood Platelets↗
PubMed1993

Computerized detection of cerebral emboli and discrimination from artifact using Doppler ultrasound.

BACKGROUND AND PURPOSE: Transcranial Doppler ultrasound can detect circulating cerebral emboli. Monitoring of patients with potential embolic sources may allow identification of high-risk patients who can then be selected for prophylactic treatment. However, practical patient monitoring will require automated programs that can detect emboli and differentiate them from artifact. METHODS: A new off-line algorithm for the detection of emboli, which detects the characteristic relative power increase occurring with an embolus, was evaluated in both an animal model and in patients. (1) In a sheep model, solid embolic materials (thrombus, platelet aggregates, and atheroma) were introduced into the proximal carotid artery while the distal carotid artery or a major branch was insonated. The signals resulting from 77 emboli (mean size, 1.77 mm) were studied and compared with the Doppler signals resulting from artifact. (2) In patients, 100 embolic signals occurring in three patients were analyzed and compared with signals associated with artifact in the same patients. RESULTS: (1) In the sheep model, emboli resulted in a short-duration, high-intensity signal, but intensity increase alone did not distinguish between emboli and artifact. In contrast, the algorithm discriminated embolus from artifact with a sensitivity of 98.7% and a specificity of 98.0%. (2) In patient studies, embolic signals were differentiated from artifact with a sensitivity of 97.2% and a specificity of 97.0% by the algorithm. CONCLUSIONS: Using such an algorithm, detection of cerebral emboli and discrimination from artifact are possible with a high sensitivity and specificity. Incorporation of such an algorithm into an on-line system should make prolonged patient monitoring practical.

Algorithms↗
PubMed1993

Surgery, angioplasty, and interventional neuroradiology.

This article discusses recent advances in the treatment of three cerebrovascular conditions, namely carotid stenosis, cerebral aneurysm, and arteriovenous malformation. In all three the aim of treatment is to prevent stroke, and in all three, recent advances in interventional neuroradiology are supplementing traditional surgical techniques. The benefits of endarterectomy for severe symptomatic carotid stenosis have been clearly demonstrated by recent trials, and early case series suggest that percutaneous transluminal angioplasty may provide an alternative treatment. Recent advances in the management of cerebral aneurysm include new treatments for cerebral vasospasm and the use of endovascular occlusion to treat inoperable aneurysms. Endovascular embolization for arteriovenous malformations also looks promising, but more randomized trials are required to establish the benefit of these interventional procedures.

Angioplasty↗