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Biomedical subjects

J M Findlay

Publications and source records attributed to J M Findlay.

At least 37 records · Page 2Linked to original sources
PubMed1998

Novel mechanism by which hemoglobin induces constriction of cerebral arteries.

Since oxyhemoglobin (OxyHb) is implicated in the pathogenesis of cerebral vasospasm, we have investigated the role of protein tyrosine phosphorylation in OxyHb-mediated signalling in canine cerebral arteries and cultured canine cerebrovascular smooth muscle cells. OxyHb produced a contraction of basilar artery preparations, which was reversed by genistein, an inhibitor of tyrosine kinases, and PD098059, an inhibitor of mitogen-activated protein kinase. In cerebrovascular smooth muscle cells, OxyHb induced tyrosine phosphorylation of 42, 46, 54-60 and 80-100 kDa proteins with a time-course which paralleled the contractile action of OxyHb, suggesting that these events might be functionally linked. The 42 and 60 kDa proteins were immunologically related to the mitogen-activated protein kinase, extracellular signal regulated protein kinase (ERK2), and to p60c-Src (c-Src), respectively. The increase in protein tyrosine phosphorylation was attenuated by genistein, and the phosphorylation of the 42 kDa protein (ERK2) was inhibited by PD098059. These results suggest that OxyHb-mediated signalling utilizes a protein tyrosine kinase-based mechanism.

Animals↗
PubMed1998

Using the eye-movement system to control the head.

We tested the hypothesis that A.I., a subject who has total ophthalmoplegia, resulting in a lack of eye movements, used her head to orientate in a qualitatively similar way to eye-based orientating of control subjects. We used four classic eye-movement paradigms and measured A.I.'s head movements while she performed the tasks. These paradigms were (i) the gap paradigm, (ii) the remote-distractor effect, (iii) the anti-saccade paradigm, and (iv) tests of saccadic suppression. In all cases, A.I.'s head saccades were qualitatively similar to previously reported eye-movement data. We conclude that A.I.'s head movements are probably controlled by the same neural mechanisms that control eye movements in unimpaired subjects.

Adult↗
PubMed1998

The area of spatial integration for initial horizontal disparity vergence.

We investigated over what central area disparity in a random dot stereogram is integrated to stimulate an initial vergence response. Vergence was measured subjectively, with a forced choice dichoptic nonius vernier task following a brief (230 msec) stimulus presentation. Stimuli were random-dot stereograms showing a central circular disc of 12.5 min arc crossed retinal disparity in front of, and occluding, a same density fixation plane surround. The size of the disc was varied. All ten observers responded to the brief stimulus. Initial vergence increased with increasing disc diameter and, for nine out of ten subjects, reached a maximum with the disc ca 6 deg, suggesting this is the extent of the spatial integration region. Below 6 deg diameter, surround and target disparities were averaged together. Initial horizontal vergence responds automatically to a cyclopean target presented in the centre of gaze by pooling disparities within a limited but surprisingly large area.

Adult↗
PubMed1998

Causes of morbidity and mortality following intracranial aneurysm rupture.

OBJECTIVE: To determine the current recovery rates and causes for morbidity and mortality in patients suffering aneurysmal subarachnoid hemorrhage (SAH). METHODS: We reviewed a recent consecutive series of 95 patients with ruptured intracranial aneurysms who presented to our hospital between 1994 and 1995. When administered, active treatment consisted of early surgery for aneurysm clipping and aggressive prevention and treatment of SAH-related complications. RESULTS: Eighty-eight (93%) of the patients were admitted within 24 hours of rupture. One-quarter of the patients in this series did not undergo aneurysm clipping due to poor neurological condition on presentation. Of the 75 patients initially considered for active treatment, 83% underwent surgery within 48 hours of rupture, all received nimodipine, 16% received tissue plasminogen activator to lyse subarachnoid or intraventricular clots, 40% underwent hypertensive treatment, and 7% underwent transluminal balloon angioplasty for vasospasm. At one year followup, 29% of patients had died, 7% had severe disabilities, 13% had moderate disabilities, 51% had made a good recovery, and 64% of all surviving patients had returned to their previous work status. Primary and contributing causes of death and disability, affecting 47 patients at one year, were: direct effects of the initial hemorrhage (79% of affected patients), surgical complications (13%), vasopasm (11%), rebleeding (11%) and medical complications (13%). CONCLUSIONS: Almost two-thirds of patients suffering aneurysm rupture make a satisfactory recovery with modern treatment. While vasospasm has become a less common cause of poor outcome following SAH, surgical complications remain an important problem.

Adult↗
PubMed1998

Carotid arteriotomy closure using a vascular clip system.

PURPOSE: To compare a newly released vascular clip system (Vascular Clip-applier System; Auto Suture Company, Norwalk, CT) designed for sutureless vessel closures and anastomoses with standard suture closure of carotid arteriotomies after carotid endarterectomies. PATIENTS AND METHODS: Sixteen consecutive patients with symptomatic and severe carotid stenoses were randomly allocated to receive either standard suture (running 6-0 monofilament) or clip artery closures after undergoing carotid endarterectomies. The speed of arteriotomy closure was calculated for each procedure, and hemostasis, complications, and postoperative carotid patency were determined and recorded for each patient. RESULTS: The clip applier system performed well, and arteriotomy closure with clips was significantly faster than suture closure (0.36 cm/min in the sutured group versus 0.52 cm/min in the clipped group, P = 0.019). Carotid patency assessed by ultrasonography 4 to 8 weeks after surgery showed that all arteries in both groups were patent. Two hemostasis problems occurred in the clip closure group, one minor that was caused by the use of incorrect clip size and one major that was probably caused by a combination of sudden arterial hypertension and clip failure. This complication resulted in a large neck hematoma and cross-clamp ischemia during the ensuing suture repair of the arterial dehiscence. CONCLUSIONS: As a result of this small study, we determined that clip closure of carotid arteriotomies was feasible, but it remains questionable whether the increased speed of a sutureless closure is clinically important for this procedure. Concerns regarding the strength of clip closure of an endarterectomized vessel and the cost of clip closure compared with standard suture techniques suggest that there may be no clinically significant benefits of arterial clip closure over suture closure after carotid endarterectomy, and there is potentially some risk.

Aged↗
PubMed1997

Guidelines for the use of carotid endarterectomy: current recommendations from the Canadian Neurosurgical Society.

OBJECTIVE: To develop guidelines on the suitability of patients for carotid endarterectomy (CEA). OPTIONS: For atherosclerotic carotid stenosis that has resulted in retinal or cerebral ischemia: antiplatelet drugs or CEA. For asymptomatic carotid stenosis: CEA or no surgery. OUTCOMES: Risk of stroke and death. EVIDENCE: Trials comparing CEA with nonsurgical management of carotid stenosis. VALUES: Greatest weight was given to findings that were highly significant both statistically and clinically. BENEFITS, HARMS AND COSTS: Benefit: reduction in the risk of stroke. Major harms: iatrogenic stroke, cardiac complications and death secondary to surgical manipulations of the artery or the systemic stress of surgery. Costs were not considered. RECOMMENDATIONS: CEA is clearly recommended for patients with surgically accessible internal carotid artery (ICA) stenoses equal to or greater than 70% of the more distal, normal ICA lumen diameter, providing: (1) the stenosis is symptomatic, causing transient ischemic attacks or nondisabling stroke (including retinal infarction); (2) there is no worse distal, ipsilateral, carotid distribution arterial disease; (3) the patient is in stable medical condition; and (4) the rates of major surgical complications (stroke and death) among patients of the treating surgeon are less than 6%. Surgery is not recommended for asymptomatic stenoses of less than 60%. Symptomatic stenoses of less than 70% and asymptomatic stenoses of greater than 60% are uncertain indications. For these indications, consideration should be given to (1) patient presentation, age and medical condition; (2) plaque characteristics such as degree of narrowing, the presence of ulceration and any documented worsening of the plaque over time; (3) other cerebral arterial stenoses or occlusions, or cerebral infarcts identified through neuroimaging; and (4) surgical complication rates at the institution. CEA should not be considered for asymptomatic stenoses unless the combined stroke and death rate among patients of the surgeon is less than 3%. VALIDATION: These guidelines generally agree with position statements prepared by other organizations in recent years, and with a January 1995 consensus statement by a group of experts assembled by the American Heart Association.

Canada↗
PubMed1997

Saccade target selection during visual search.

Five experiments are reported in which eye movements were recorded while subjects carried out a visual search task. The aim was to investigate whether an accurate initial target directed saccade could be programmed. In experiments 1-2, subjects moved their eyes to targets defined by colour, which were presented with seven non-targets in a circular array. Accurate saccades with short latencies were common but errors sometimes occurred and search for an "oddity" target, defined exclusively by difference in colour from a homogeneous set of distractors, was particularly error prone. In Experiment 3, occasional trials contained double targets. First saccades sometimes landed at an intermediate position between the targets. In Experiments 4 and 5, targets were presented with 15 distractors in two concentric rings of 8. Targets specified by shape could be located accurately with a single saccade. Search for a colour-shape conjunction was more difficult but targets in the inner ring were located frequently with a single saccade. The results suggest that the control of the initial eye movement during both simple and conjunction searches is through a spatially parallel process.

Adult↗
PubMed1997

Spatial scale and saccade programming.

The global effect in eye orienting occurs when saccades land at the 'centre of gravity' of a target stimulus configuration. Short-latency saccades are particularly prone to this effect whereas longer-latency saccades may show more influence of fine detail. Alternative explanations of these effects are considered and data are presented from an experiment in which the influence of different stimulus features on the global effect in a search task was examined. The effect shows a substantially different time course for target-distractor combinations differing in contrast polarity (black vs white) than for combinations differing in shape (circle vs square). It is concluded that the global effect cannot be explained either as a high-level strategic effect or as an effect of automatic fast processing of low-spatial-frequency information in early sensory channels. Instead it is suggested that the visual-spatial-integration characteristic of the global effect is an integral and unavoidable part of the process of selection of saccadic response.

Humans↗
PubMed1997

The effect of depth rotation on object identification.

Five experiments are reported in which the time to verify the name of different three-dimensional common objects shown rotated in depth was investigated. Views of computer-generated images of elongated objects rotated in steps of 30 degrees along six axes of rotation were used as stimuli. A significant main effect of view was found in all experiments. This effect was initially attributed to the relatively slower verification times to the end-on views of objects but further analysis revealed that views 30 degrees off the end-on views were significantly slower to verify than other views. Objects with gravitational uprights yielded the same effects as objects without gravitational uprights. The results were not dependent on practice with the stimuli prior to the experiment or on repeated exposure of the views during the experiment. Also, there was no benefit found for the identification of shaded over silhouetted images of objects when shown in more-conventional views but unconventional views were more recognisable when shaded than when silhouetted. Last, initial verification times for familiar views of a set of novel objects were faster than for unfamiliar views even when the views were unconventional. With practice on unfamiliar views, however, the same function relating view to verification time found for familiar objects was found for the novel objects. The results suggest that for recognition purposes visual memory stores discrete views of objects but it characteristically favours a canonical range of views of elongated objects that are based on the salient geometry of the objects so that more unconventional or foreshortened views are less readily recognised.

Adult↗
PubMed1997

Face detection in peripheral vision: do faces pop out?

We examined whether faces can produce a 'pop-out' effect in visual search tasks. In the first experiment, subjects' eye movements and search latencies were measured while they viewed a display containing a target face amidst distractors. Targets were upright or inverted faces presented with seven others of the opposite polarity as an 'around-the-clock' display. Face images were either photographic or 'feature only', with the outline removed. Naive subjects were poor at locating an upright face from an array of inverted faces, but performance improved with practice. In the second experiment, we investigated systematically how training improved performance. Prior to testing, subjects were practised on locating either upright or inverted faces. All subjects benefited from training. Subjects practised on upright faces were faster and more accurate at locating upright target faces than inverted. Subjects practised on inverted faces showed no difference between upright and inverted targets. In the third experiment, faces with 'jumbled' features were used as distractors, and this resulted in the same pattern of findings. We conclude that there is no direct rapid 'pop-out' effect for faces. However, the findings demonstrate that, in peripheral vision, upright faces show a processing advantage over inverted faces.

Adult↗
PubMed1997

Hemodynamic instability after carotid endarterectomy: risk factors and associations with operative complications.

OBJECTIVE: To examine the incidences of hypertension, hypotension, and bradycardia after carotid endarterectomy (CEA) and to identify any hemodynamic variables predictive of postoperative stroke, death, or cardiac complications. METHODS: Retrospective population-based cohort study of 291 consecutive patients undergoing CEA using hospital chart review. Hemodynamic data collected from time of arrival in the recovery room until the end of the 1st postoperative day. Primary and secondary outcome events were stroke or death within 30 days of surgery and any postoperative cardiac complication (angina, congestive heart failure, dysrhythmia, or myocardial infarction), respectively. RESULTS: The incidences of postoperative hypertension (systolic blood pressure > 220 mm Hg), hypotension (systolic blood pressure < 90 mm Hg), and bradycardia (pulse < 60 beats/min) were 9% (26 of 290 cases), 12% (36 of 290 cases), and 55% (159 of 290 cases), respectively. The stroke or death rate was 5.2% (15 of 291 cases). Postoperative hypertension was associated significantly with stroke or death (P = 0.04) and by a statistical trend with cardiac complications (P = 0.07). Independent preoperative risk factors for postoperative hypertension by multivariate analysis included angiographic intracranial carotid stenosis greater than 50%, cardiac dysrhythmia, preoperative systolic blood pressure greater than 160 mm Hg, neurological instability, and renal insufficiency. Postoperative hypotension and bradycardia did not correlate with primary or secondary outcomes. CONCLUSION: Hemodynamic instability was commonly observed after CEA, but only postoperative hypertension was associated with stroke or death and, possibly, with cardiac complications. Patients undergoing CEA, especially those at risk for postoperative hypertension, may be monitored best in settings suited to the expeditious management of neurological and cardiovascular emergencies.

Aged↗
PubMed1997

Experience with computed tomographic angiography for the detection of intracranial aneurysms in the setting of acute subarachnoid hemorrhage.

OBJECTIVE: To objectively compare computed tomographic angiography (CTA) with selective digital subtraction angiography (DSA) in the detection and anatomic definition of intracranial aneurysms, particularly in the setting of acute subarachnoid hemorrhage (SAH). METHODS: In a blinded prospective study, 40 patients with known or suspected intracranial saccular aneurysms underwent both CTA and DSA, including 32 consecutive patients with SAH in whom CTA was performed after CT images were obtained diagnostic for SAH. The CT angiograms were interpreted for presence, location, and size of the aneurysms, and anatomic features, such as the number of aneurysms lobes, aneurysm neck size (< or = 4 mm), and the number of adjacent arterial branches were suggested. The images obtained with CTA were then compared with the images obtained with DSA, with the later images serving as controls. RESULTS: DSA revealed 43 aneurysms in 30 patients and ruled out intracranial aneurysms in the remaining 10 patients. For aneurysm presence alone, the sensitivity and specificity for CTA was 86 and 90%, respectively. For the presence of an aneurysms, six CT angiogram showed false negative results and one CT angiogram showed a false positive result. False negative results were usually caused by technical problems with the image, tiny aneurysm domes (< 3 mm), and unusual aneurysm locations (i.e., intracavernous carotid or posterior inferior cerebellar artery aneurysms). The results obtained with CTA were, compared with the results obtained with DSA, more than 95% accurate in determining dome and neck size of aneurysm, aneurysm lobularity, and the presence and number of adjacent arterial branches. In addition, CTA provided a three-dimensional representation of the aneurysmal lesion, which was considered useful for surgical planning. CONCLUSION: CTA is useful for rapid and relatively noninvasive detection of aneurysms in common locations, and the anatomic information provided in images showing positive results is at least equivalent to that provided by DSA. In cases of SAH in which the nonaugmented CT and CTA results indicate a clear source of bleeding and provide adequate anatomic detail, we think it is possible to forego DSA before urgent early aneurysm surgery. In all other cases, DSA is indicated.

Acute Disease↗
PubMed1997

Carotid endarterectomy in the presence of a persistent hypoglossal artery: case report.

OBJECTIVE AND IMPORTANCE: A persistent hypoglossal artery, one of the embryonic carotid-basilar anastomoses that can fail to regress in the embryo and can be observed past birth, is one of the only congenital anatomic variations of the internal carotid artery (ICA) that can complicate the performance of carotid endarterectomy. When associated with atherosclerotic carotid artery disease, the recognition and intraoperative management of a persistent hypoglossal artery is important. CLINICAL PRESENTATION: A 72-year-old man presented with a symptom of transient right hemisphere ischemia, and although ultrasonography indicated a right ICA stenosis (and no other abnormality), angiography also demonstrated that the atherosclerotic plaque extended into the origin of a large right persistent hypoglossal artery arising 1.5 cm from the origin of the ICA. In this patient, the persistent hypoglossal artery was the only arterial supply to the basilar artery. INTERVENTION: The patient underwent a right ICA endarterectomy, and intraoperative angiography was necessary to ensure that the persistent hypoglossal artery was the vessel shunted during the arterial repair. CONCLUSION: Recognition of the primitive carotid-basilar anastomoses is important to surgeons who perform carotid endarterectomy and is not possible with ultrasonography alone. Intraoperative angiography enables the surgeon to accurately catheterize a persistent hypoglossal artery with a carotid shunt.

Basilar Artery↗
PubMed1997

Effect of remote distractors on saccade programming: evidence for an extended fixation zone.

In a series of experiments, we examined the increase in saccade latency that is observed consistently when distractor stimuli are presented simultaneously with the saccade target at various nontarget locations. In the first experiment, targets and distractors were presented on the horizontal axis. We found that saccade latency was increased when distractors appeared at fixation and in the contralateral nontarget hemifield (at eccentricities < or = 10 degrees). In contrast, latency was unaffected by distractors presented along the ipsilateral target axis, but amplitude was increased as saccades tended to land at intermediate locations between the two stimuli (global effect). The effect of presenting distractors at various two-dimensional locations in both the target and nontarget hemifields then was examined, and the maximum latency increase again was observed when distractors appeared at fixation. Distractors presented on any of the eight principal axes in either hemifield, other than on the horizontal target axis, also increased latency. The relationship between the effects of distractors on latency and amplitude was reciprocal. Within approximately 20 degrees of the target axis itself, distractors affected saccade amplitude but not latency. In contrast, distractors presented outside this "window" increased saccade latency without affecting amplitude. A systematic quantitative relationship was revealed between the increase in latency and the ratio between target and distractor eccentricities. The latency increase was largest with small values of the ratio and reached a peak with distractors at the fixation location. The finding that the increase observed for more eccentric distractor locations fitted the same function as that at fixation shows that inhibitory effects operate over large areas of the visual field. The increase in latency under distractor conditions is interpreted in light of recent neurophysiological findings of inhibitory processes operating in the rostral region of the superior colliculus. Our results suggest that these inhibitory processes are not restricted to the central foveal region alone but operate over wider regions of the visual field.

Adult↗
PubMed1997

Regional performance of carotid endarterectomy. Appropriateness, outcomes, and risk factors for complications.

BACKGROUND AND PURPOSE: Guided by the findings of randomized controlled trials evaluating carotid endarterectomy (CEA), we examined the appropriateness of CEAs performed in our city and determined the incidences and risk factors for postoperative stroke, death, and cardiac complications. METHODS: Using health records, we retrospectively reviewed 291 consecutive CEAs performed in our region over 18 months. Based on randomized controlled trial results and standardized remeasurements of angiographic carotid stenoses, indications for CEA were considered appropriate for symptomatic carotid stenoses > or = 70%, uncertain for < 70% symptomatic or > or = 60% asymptomatic stenoses, or inappropriate for < 60% asymptomatic stenoses and for patients with preoperative neurological or medical instability. RESULTS: We found that 41% of patients (118/291) were asymptomatic. Surgical indications were appropriate in 33% of cases (92/281), uncertain in 49% (138/281), and inappropriate in 18% (51/281). Stroke or death occurred within 30 days postoperatively in 5.2% (9/174) of symptomatic patients and 5.1% (6/117) of asymptomatic patients. At least one cardiac complication (angina, congestive heart failure, dysrhythmia, or myocardial infarction) developed in 8.9% (26/291). Independent preoperative risk factors for stroke or death were histories of angina or congestive heart failure and lack of antiplatelet medication; for cardiac complications, risk factors were age > 75 years and a history of congestive heart failure. CONCLUSIONS: Almost 1 in 5 patients underwent CEA inappropriately, which was most commonly due to apparent over-estimation of stenosis severity, and half had uncertain indications. Our high complication rate possibly negated any overall surgical benefit in the large group of asymptomatic patients.

Aged↗
PubMed1997

In vivo angioplasty prevents the development of vasospasm in canine carotid arteries. Pharmacological and morphological analyses.

BACKGROUND AND PURPOSE: To study the effects of in vivo transluminal balloon angioplasty (TBA) on the structure and function of the arterial wall, a canine model of hemorrhagic cerebral vasospasm of the high cervical internal carotid artery (ICA) was used. This model was also used to determine whether TBA performed before clot placement could prevent the development of vasospasm. METHODS: Twelve dogs underwent surgical exposure of both distal-cervical ICAs, followed by baseline angiography. One randomly selected ICA in each dog was then subjected to in vivo TBA and repeated angiography. Both distal ICAs were then surrounded with blood clots held by silicone elastomer sheaths. Seven days later angiography was repeated, and all animals were killed. The ICAs in four animals were perfusion-fixed in situ for morphological analysis by electron microscopy, and the arteries in the remaining eight animals were removed and immediately immersed in oxygenated Krebs' solution. Contractile responses of isolated arterial rings from each ICA were recorded after treatment with KCl, noradrenaline, serotonin, and prostaglandin F2 alpha, while relaxations in response to the calcium ionophore A23187 and papaverine were recorded after tonic contraction to noradrenaline had been established. The morphology and pharmacological responses of ICAs that had been exposed to blood with or without prior TBA were compared with data obtained from control arterial segments of intact, more proximal regions of the ICAs from each animal. RESULTS: TBA resulted in immediate angiographic enlargement of the ICA lumen that was still evident 7 days later despite the placement of clotted blood around the artery. Scanning and transmission electron microscopy demonstrated flattening of the intima and internal elastic lamina in these dilated arteries, associated with patchy losses of endothelial cells. In contrast, ICAs that had been exposed to clotted blood but had not undergone prior TBA developed consistent angiographic and morphological vasospasm. In comparison with control vessels and nondilated vasospastic vessels, vessels dilated with TBA and then exposed to clotted blood showed significantly diminished responses to all compounds tested, with the exception of prostaglandin F2 alpha. CONCLUSIONS: These results indicate that in vivo TBA results in a degree of functional impairment of vascular smooth muscle that persists for at least 7 days. This result is consistent with previous observations of the acute effects of TBA in isolated arteries. Furthermore, these results support the hypothesis that normal smooth muscle function is required for the development of vasospasm. Finally, these results indicate that TBA performed before the onset of vasospasm prevents its development.

Angiography↗