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Biomedical subjects

M Arnold

Publications and source records attributed to M Arnold.

At least 37 records · Page 2Linked to original sources
PubMed2004

Cerebrovascular response to repetitive visual stimulation in interictal migraine with aura.

Cortical hypersensitivity and absent habituation to different stimuli have been observed in migraine patients. These features might also be transmitted to the cerebral vasoreactivity, but results are conflicting so far. Transcranial Doppler ultrasound (TCD) was used to assess cerebral blood flow velocity (CBFV) changes in the middle (MCA) and posterior cerebral arteries (PCA) in relation to repetitive checkerboard visual stimulation. Stimulation consisted of 10 consecutive cycles, each comprising 10 s stimulation and 10 s rest. TCD recordings were analysed using stimulus-related averaging algorithm. Data of 19 interictal migraineurs with aura were compared to those of 19 headache-free healthy volunteers. The CBFV increase in PCA and in MCA during visual stimulation was significantly larger and steeper in migraineurs than in controls (P = 0.017 and P = 0.005). The response in PCA remained stable over the 10 stimulation cycles, both in migraineurs and in controls. The response in MCA was stable only in migraineurs. In controls it decreased over the last 5 stimulation cycles compared with the first 5 cycles (P = 0.04). Migraineurs with aura exhibit a larger cerebrovascular response to repetitive visual stimulation compared to headache-free subjects. A reduced adaptation to environmental stimuli in migraine is suggested, since there was no habituation in migraineurs in contrast to healthy controls.

Adult↗
PubMed2004

Clinical and radiological predictors of recanalisation and outcome of 40 patients with acute basilar artery occlusion treated with intra-arterial thrombolysis.

OBJECTIVE: To define predictors of recanalisation and clinical outcome of patients with acute basilar artery occlusions treated with local intra-arterial thrombolysis (IAT). METHODS: Vascular risk factors, severity of the neurological deficit graded by the National Institutes of Health stroke scale (NIHSS), and radiological findings were recorded at presentation. Outcome was measured using the modified Rankin scale (mRS) three months later and categorised as favourable (mRS 0-2), poor (mRS 3-5), or death (mRS 6). RESULTS: 40 patients were studied. Median NIHSS on admission was 18. Mean time from symptom onset to treatment was 5.5 hours (range 2.3 to 11). Outcome was favourable in 14 patients (35%) and poor in nine (23%); 17 (42%) died. There were two symptomatic cerebral haemorrhages (5%). Recanalisation of the basilar artery was achieved in 32 patients (80%); it was complete (TIMI grade 3) in 20% and partial (TIMI grade 2) in 60%. In multivariate logistic regression analysis, low NIHSS score on admission (p = 0.002) and vessel recanalisation (p = 0.005) were independent predictors of favourable outcome. Recanalisation occurred more often with treatment within six hours of symptom onset (p = 0.003) and when admission computed tomography showed a hyperdense basilar artery sign (p = 0.007). In a univariate model, quadriplegia (p = 0.002) and coma (p = 0.004) were associated with a poor outcome or death. CONCLUSIONS: Low baseline NIHSS on admission and recanalisation of basilar artery occlusions predict a favourable outcome after intra-arterial thrombolysis. Early initiation of IAT and the presence of a hyperdense basilar artery sign on CT were associated with a higher likelihood of recanalisation.

Acute Disease↗
PubMed2003

Diffusion-weighted MRI in acute spinal cord ischaemia.

Acute spinal cord ischaemia is often undetectable with conventional MRI. Diffusion-weighted MRI (DWI) has been difficult to use in the spine because of susceptibility artefacts. We assessed the diagnostic value of echoplanar DWI for early confirmation of spinal cord ischaemia. We performed conventional MRI and DWI in two men and three women, aged 54-75 years with clinically suspected acute spinal cord ischaemia. Imaging was performed 9-46 h after the onset of symptoms, and 2-9 days later to assess the extent of ischaemic signal change. Spatial resolution of DWI within the spine using standard equipment was poor, but in all patients, early DWI revealed areas of high signal indicating decreased diffusion, confirmed by measurement of apparent diffusion coefficients. Follow-up MRI showed high signal on T2-weighted images and contrast enhancement at the expected levels. Neurological deficits corresponded with radiological findings in four patients: various syndromes, including isolated bilateral weakness or sensory change and combined deficits, were found. Echoplanar DWI may be helpful for confirmation of spinal cord ischaemia in the acute stage, but follow-up T2-weighted images have superior spatial resolution and correlation with clinical findings and lesion extent.

Acute Disease↗
PubMed2003

Carotid dissection with permanent and transient occlusion or severe stenosis: Long-term outcome.

OBJECTIVE: To compare the rate of ischemic events and intracranial hemorrhage in the long-term follow-up of patients with persistent and transient severe stenosis or occlusion of the internal carotid artery (ICA) due to spontaneous dissection (ICAD). METHODS: One hundred and sixty-one consecutive patients with unilateral ICAD causing severe stenosis or occlusion were examined clinically and by ultrasound 1 year after symptom onset. Forty-six cases with persistent and 46 age- and latency-matched cases with transient (recanalization complete or less than 50% stenosis) severe stenosis or occlusion of the ICA were enrolled. Nine patients with surgical, endovascular, or fibrinolytic therapy for ICAD or associated stroke were excluded. Antithrombotic therapy was given at the discretion of the treating physician. Clinical follow-ups were done annually. RESULTS: Antithrombotic therapy and follow-up were similar in patients with permanent (6.2 +/- 3.4 years) and transient (7.2 +/- 4.3 years) severe stenosis or occlusion of the ICA. Cases with permanent carotid stenosis or occlusion showed annual rates of 0.7% for ipsilateral carotid territory stroke and of 1.4% for any stroke. Cases with transient carotid stenosis or occlusion showed annual rates of 0.3% for ipsilateral carotid territory stroke and of 0.6% for any stroke. CONCLUSIONS: This study suggests that ICAD has a benign long-term prognosis with low rates of ipsilateral carotid territory and any stroke and that the stroke rate in ICAD is not related to the persistence of severe carotid stenosis or occlusion. These results question the rationale of surgical or catheter-based revascularization in patients with ICAD.

Adult↗
PubMed2003

[Anticoagulation and antiaggregation in neurological patients].

Aspirin is the drug of choice in most patients with acute stroke, if thrombolysis is contraindicated. Heparin is only used in acute stroke due to cerebral venous thrombosis, extracranial carotid or vertebral artery dissection and cardiac emboli with high risk of recurrence. In the prevention of recurrent stroke in patients with a noncardioembolic ischemic stroke antiplatelet agents are used. Aspirin is the first-line agent. Clopidogrel or a combination aspirin/dipyridamol are recommended for patients with several risk factors or recurrent cerebrovascular events. Warfarin has demonstrated a clear efficacy in stroke prevention in patients with atrial fibrillation, cerebral venous thrombosis and antiphospholipid antibody syndrome. Other, less well established possible indications for warfarin in the secondary prevention of stroke are symptomatic intracranial artery stenosis, large aortic atheroma, extracranial carotid or vertebral artery dissection and patent foramen ovale.

Acute Disease↗
PubMed2003

[Stroke prevention].

Life style modification has been shown to reduce stroke risk. In patients with risk factors several drugs have proven their efficacy. The most effective medications are antihypertensives, antidiabetics, statins and antithrombotics. In the prevention of recurrent stroke in patients with a noncardioembolic ischemic stroke antiplatelet agents are used. Aspirin or a combination aspirin/dipyridamol are the first-line agents. Clopidogrel is recommended for patients with aspirin intolerance, several risk factors or recurrent cerebrovascular events. Warfarin has demonstrated efficacy in stroke prevention in patients with cardioembolic stroke, cerebral venous thrombosis and antiphospholipid antibody syndrome. Other, less well established indications for warfarin in the secondary prevention of stroke are: symptomatic intracranial artery stenosis; large aortic atheroma and extracranial carotid or vertebral artery dissection.

Administration, Oral↗
PubMed2003

[Health services research: subject matter and objectives of a field at the intersection of economics, medicine and ethics].

In analogy to the famous saying that war is too serious to leave it to the generals, one could say that the provision of medical care is too serious and too costly to leave it to doctors. This, however.would give the impression of an incongruity which does not exist as an actual factor or as a standpoint in research on the healthcare system. Having said that, there are differences in the methods of observation used: doctors always base their observations on their experiences at the doctor/patient level. In these situations, they are influenced by the therapeutic imperative of wanting to help and their convictions do not allow them to take into account competing requirements or to feel dependent on the higher-level conditions; and the realm of research on the health care system bases its observations more or less on findings derived by means of analysing what is often highly aggregated data, be it of a medical, economic or epidemiological nature. Even though the insights gained at the macrolevel ultimately have to be applied at the microlevel of the doctor/patient relationship, there remains an internal distance from the problems of care which is conducive to proper judgement. From this distant vantage point, researchers attempt to prove the relationship between effort and yield, to indicate weak spots which individual doctors cannot recognise and to define capacity, structure and incentive conditions which guarantee maxi-mum medical care quality. There is, for instance, evidence of astonishing dependence between the medical care provided and incentives for the number of doctor/patient contacts, use of medicines, surgery rates and number of diagnoses. This evidence can be used to draw up recommendations for self-governing bodies in the health care sector and for the political sphere as to how the health care system could be enhanced to achieve a high level of efficiency and quality.

Adolescent↗
PubMed2003

Recanalisation of cerebral venous thrombosis.

OBJECTIVE: To investigate recanalisation in the first 12 months after cerebral venous thrombosis. METHODS: 33 consecutive patients presenting with cerebral venous thrombosis were enrolled in the study. Diagnosis was made by magnetic resonance imaging (MRI) and magnetic resonance venography (MRV) or catheter angiography. Patients were initially treated with intravenous heparin. Warfarin was given for at least four months. Cerebral MRI and MRV were done at four months and repeated after 12 months if venous thrombosis persisted. Outcome was evaluated by the Rankin scale at 12 months. RESULTS: Outcome at 12 months was good, with a median modified Rankin scale score of 0 (range 0 to 2); 27 patients (82%) had no residual deficits. No patient suffered recurrent cerebral venous thrombosis, deep vein thrombosis, or pulmonary embolism during follow up. After four months, all deep cerebral veins and cavernous sinuses, 94% of superior sagittal sinuses, 80% of straight sinuses, 73% of jugular veins, 58% of transverse sinuses, and 41% of sigmoid sinuses had recanalised. No further recanalisation was observed thereafter. CONCLUSIONS: The results suggest that recanalisation only occurs within the first four months following cerebral venous thrombosis and not thereafter, irrespective of oral anticoagulation.

Adult↗
PubMed2003

Intra-arterial thrombolysis in 24 consecutive patients with internal carotid artery T occlusions.

OBJECTIVES: To determine the safety, efficacy, and predictors of favourable outcome of intra-arterial thrombolysis in acute stroke attributable to internal carotid "T"occlusion METHODS: The authors analysed 24 consecutive patients with T occlusions of the internal carotid artery treated by local intra-arterial thrombolysis using urokinase. RESULTS: The median baseline National Institutes of Health Stroke Scale was 19. The average time from symptom onset to treatment was 237 minutes. Four patients (16.6%) had a favourable (modified Rankin Scale score (mRS</=2)) and 10 patients (41.7%) a poor outcome (mRS 3 or 4) after three months. Ten patients (41.7%) died. One symptomatic intracerebral haemorrhage (4.2%) occurred. Partial recanalisation of the intracranial internal carotid artery was achieved in 15 (63%), of the middle cerebral artery in four (17%), and of the anterior cerebral artery in eight patients (33%). Complete recanalisation never occurred. Sufficient leptomeningeal collaterals as seen on arteriography (p=0.02) and age <60 years (p=0.012) were the only predictors of favourable clinical outcome. CONCLUSIONS: Acute stroke attributable to carotid T occlusion remains a condition with a generally poor prognosis even when intra-arterial thrombolysis is performed. Favourable outcome was seen only in patients with sufficient leptomeningeal collaterals.

Adult↗
PubMed2002

Assessing the efficacy of a ram-genotyping programme to reduce susceptibility to scrapie in Great Britain.

Susceptibility to clinical scrapie is associated with polymorphisms in the PrP gene. The 'ARR' allele of this gene reduces susceptibility to clinical disease caused by all known strains of the transmissible spongiform encephalopathy (TSE) agent. The British government proposes to use a ram-genotyping scheme to breed genetic resistance to clinical scrapie into the national sheep population. We considered how best to target limited genotyping resources to achieve the maximum rate of genotype evolution. We created a metapopulation model of the British sheep industry, which includes the major pure-breeds of sheep and the cross-breeds produced by crossing these pure-bred animals. The main criterion for assessing the efficacy of different strategies was the time taken to increase the prevalence of the ARR allele in the slaughter-lamb population. Our model predicted that the most-effective strategy would be to target genotyping to those rams used for pure-breeding (i.e. mated with the same breed of ewe). This strategy was compared to two further strategies, in which the proportion of rams genotyped in each breed depended on the prevalence of the ARR/ARR genotype in that breed. A policy in which the proportion of animals genotyped is reduced as the ARR prevalence in that breed increases is efficient. The most-effective policy was targeting the hill sector in the early years and gradually switching to genotyping more terminal-sire and longwool rams as the resistance of the hill sector increases.

Animal Husbandry↗
PubMed2002

Apparent diffusion coefficient mapping of infarcted tissue and the ischaemic penumbra in acute stroke.

MRI assessment of diffusion changes in acute cerebral ischaemia necessitates analysis of the apparent diffusion coefficient (ADC). We used the concept of relative weighted mean ADC (rwmADC) to obtain an accurate estimate of the extent of infarcted tissue. We studied ten patient with of acute ischaemic stroke, using diffusion- and perfusion- weighted MRI. The rwmADC was used to calculate a corrected ADC-lesion volume (DLVR), which was compared with the diffusion-lesion volume (DLV), initial perfusion lesion volumes and the follow-up infarct volume on T2-weighted images. We looked at correlations between the MRI and clinical findings. DLVR was closest to the final infarct size and had the best clinicoradiological correlation (r=0.77). Weighting the mean ADC within the ischaemic and normal parenchyma can give a more correct estimate of the volume of infarcted brain parenchyma, thus improving the definition of the penumbra.

Brain↗
PubMed2002

[Stroke as an emergency].

Patients with acute ischemic stroke can be treated by intravenous thrombolysis within 3 hours or by intraarterial thrombolysis within 6 hours of symptom onset. Thrombolysis leads to an absolute reduction of a long term disability of 11-15% in selected patients. Aspirin is the drug of choice in most patients with acute stroke, if thrombolysis is contraindicated. Heparin is only used in acute stroke patients with high risk of recurrence. The diagnosis and treatment of medical and neurological complications remain crucial in the management of acute stroke.

Acute Disease↗
PubMed2002

Outcome of patients with cryptogenic stroke and patent foramen ovale.

OBJECTIVES: The aim was to estimate the recurrence rate and to define subgroups at increased risk for recurrent cerebral ischaemia in patients with patent foramen ovale (PFO) and so called cryptogenic stroke due to paradoxical embolism. METHODS: Patent foramen ovale was diagnosed in 318 patients with otherwise unexplained ischaemic stroke or transient ischaemic attack (TIA). One hundred and fifty nine were treated medically (oral anticoagulation 79, platelet inhibitors 80) and represent the study population. The remaining 159 patients underwent endovascular or surgical closure of the PFO and are not part of this study. RESULTS: Mean age was 50.7 (SD 13.5) years. The event leading to the diagnosis of PFO was a TIA in 38 patients (23.9%), an ischaemic stroke in 119 (74.8%), and an amaurosis fugax in two patients (1.3%). Forty four patients (27.7%) had experienced multiple cerebrovascular ischaemic events before the diagnosis of the PFO. During mean follow up of 29 (SD 23) months 21 patients (13.4%) had a recurrent cerebrovascular event (seven strokes and 14 TIAs). The average annual rate of recurrent strokes was 1.8% and that of recurrent strokes or TIAs was 5.5%. When patients with PFO with multiple cerebrovascular events before the diagnosis of the PFO were analyzed separately, the average annual rates of recurrent cerebral ischaemia were 3.6% for recurrent strokes and 9.9% for recurrent strokes or TIAs. These rates were significantly higher than in patients with first ever stroke or TIA (p=0.02). CONCLUSIONS: The study confirms a risk of stroke recurrence that is similar to the rates of previously published series of patients with PFO and cryptogenic strokes. Patients with more than one previous event were at increased risk of recurrent cerebral ischaemia.

Adolescent↗
PubMed2002

[Brief causal relations in EEG based on adaptive Granger causality].

Commonly, coherence and correlation are used to describe interrelations between EEG signals. But, on this basis, the investigation of causality or direction of interrelations is not possible. The general idea of causality between two signals may be expressed in terms of upgrading the predictability of one signal bye the knowledge of the past of the other signal. The best established approach in this context is the so-called Granger causality. The study present an adaptive estimation of Granger causality, which allows to detect dynamic causal relations within time intervals of less 100 ms. The time-variant Granger causality is applied to EEG data of the Stroop task. It could be shown, that conflict situation generates a dense web of directed interactions from posterior to anterior cortical areas.

Adult↗
PubMed2001

Mediterranean Sea surface radiocarbon reservoir age changes since the last glacial maximum.

Sea surface reservoir ages must be known to establish a common chronological framework for marine, continental, and cryospheric paleoproxies, and are crucial for understanding ocean-continent climatic relationships and the paleoventilation of the ocean. Radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over Mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one (approximately 400 years) during most of the past 18,000 carbon-14 years. However, reservoir ages increased by a factor of 2 at the beginning of the last deglaciation. This is attributed to changes of the North Atlantic thermohaline circulation during the massive ice discharge event Heinrich 1.

Animals↗
PubMed2001

Prognosis after percutaneous closure of patent foramen ovale for paradoxical embolism.

The long-term risk and risk factors for recurrent embolism after percutaneous closure of patent foramen ovale (PFO) were investigated in 152 consecutive patients with presumed paradoxical embolism. During follow-up, the actuarial freedom from recurrent embolism was 95.1% at 1 year, and 90.6% at 2 and 6 years. A residual shunt after percutaneous PFO closure was a predictor for recurrence (RR 5.3; 95% CI 1.3 to 21.0; p = 0.02). Randomized trials comparing medical treatment with percutaneous PFO closure in the prevention of recurrent embolism are in progress.

Adult↗
PubMed2001

Palaeolithic paintings. Evolution of prehistoric cave art.

Sophisticated examples of European palaeolithic parietal art can be seen in the caves of Altamira, Lascaux and Niaux near the Pyrenees, which date to the Magdalenian period (12,000-17,000 years ago), but paintings of comparable skill and complexity were created much earlier, some possibly more than 30,000 years ago. We have derived new radiocarbon dates for the drawings that decorate the Chauvet cave in Vallon-Pont-d'Arc, Ardèche, France, which confirm that even 30,000 years ago Aurignacian artists, already known as accomplished carvers, could create masterpieces comparable to the best Magdalenian art. Prehistorians, who have traditionally interpreted the evolution of prehistoric art as a steady progression from simple to more complex representations, may have to reconsider existing theories of the origins of art.

Archaeology↗