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Biomedical subjects

D Linden

Publications and source records attributed to D Linden.

At least 37 records · Page 2Linked to original sources
PubMed1996

Transcranial Doppler during neurocardiogenic syncope.

The purpose of the present study was to investigate changes in cerebral circulation during neurocardiogenic syncope (NCS). Twenty patients with a history of unexplained syncopes were studied over a 45 min period in a tilted position. Heart rate and arterial blood pressure were recorded non-invasively using Finapres. Cerebral blood flow velocity of both middle cerebral arteries was measured with transcranial Doppler (TCD). Ten patients (50%) developed a NCS during the tilt test, with a strong reduction in blood pressure (mean, 48/34 mmHg) and heart rate (mean, 54 beats/min). Simultaneously, diastolic blood flow velocities dropped to values close to zero. However, systolic blood flow velocities did not decrease. In consequence, the pulsatility index (PI) increased considerably from 0.93 to 2.01. The increase in PI suggests that there is a constriction of cerebral resistance vessels during NCS. Despite the drop in blood pressure and the putative increase in cerebrovascular resistance, systolic blood flow velocities remained unchanged in the TCD records. This fact can be explained by a lumen narrowing of the middle cerebral artery at the site of insonation. In conclusion, the typical changes in cerebral blood flow velocity during NCS are probably due to a strong constriction of both the proximal and the peripheral segments of cerebral arteries. It is clear that, in addition to vasodepression and cardiac inhibition, cerebral vasoconstriction is a further mechanism in the pathogenesis of a NCS.

Adult↗
PubMed1995

Subclinical autonomic disturbances in multiple sclerosis.

We compared results from non-invasive autonomic testing [sympathetic skin responses (SSR), heart beat variation during deep breathing, and orthostatic manoeuvre with transcranial Doppler monitoring in 22 patients] with motor and somatosensory evoked potentials (MEP and SEP) in 30 unselected patients with multiple sclerosis. We found a similarly high yield of pathological results for SSR, MEP and SEP (66.7%, 65.5%, and 69%, respectively). When analysed for each limb (n = 120), SSR were highly correlated with MEP and SEP (for both P < 0.001). Heart beat variation was reduced in only 3 patients. In 4 of 22 patients orthostatic manoeuvre induced a pathological decrease in cerebral blood flow velocity despite normal systemic blood pressure being maintained. We conclude that SSR may be a useful additional diagnostic tool in patients with multiple sclerosis. Cerebral dysautoregulation is a rather frequent finding, although its significance is not known.

Adolescent↗
PubMed1995

Sympathetic skin responses (SSRs) in monofocal brain lesions: topographical aspects of central sympathetic pathways.

Lesions of the central sympathetic pathways are likely to be of clinical relevance. In patients with acute stroke, in particular, they may be responsible for the partially deleterious cardiac arrhythmia. There is little knowledge of the central organization of sympathetic pathways above the brainstem level for both cardio-efferent and sudomotor fibers. We studied the sympathetic skin response (SSR) in 29 patients with brainstem stroke or infarction in the territory of the middle cerebral artery (MCA) in order to evaluate the pathways mediating emotional sweating. In 24 patients (82.8%) the SSR was pathological. These abnormalities were bilateral with no clear asymmetry in 10 patients (34.5%), bilateral with marked contralateral pathology in 8 patients (27.6%), purely contralateral in 5 patients (17.2%) and purely ipsilateral in one patient (3.5%). Bilateral abnormalities were more frequent and more marked in brainstem than in MCA stroke. This is probably indicative of a more generalized sympathetic dysfunction. In contrast, contralateral abnormalities were more pronounced in MCA than in brainstem infarcts. Our results show that sympathetic skin responses are suppressed in the majority of stroke patients. Asymmetric responses may indicate that sudomotor fibers mediating emotional sweating have their origin or receive input from the contralateral MCA territory.

Adult↗
PubMed1995

Phase relationship between cerebral blood flow velocity and blood pressure. A clinical test of autoregulation.

BACKGROUND AND PURPOSE: This study investigates the usefulness, as a test of dynamic autoregulation, of phase shift angle analysis between oscillations in cerebral blood flow velocity (CBFV) and in arterial blood pressure (ABP) during deep breathing. METHODS: Fifty healthy volunteers, 20 patients with occlusive cerebrovascular diseases (OCD), and 10 patients with arteriovenous malformations (AVM) took part in the study. All subjects received transcranial Doppler monitoring of both middle cerebral arteries (MCAs). In addition, continuous blood pressure monitoring was performed with the use of noninvasive servo-controlled infrared finger plethysmography during deep breathing at a rate of 6/min. With the use of a high-pass filter model of autoregulation, autoregulation was quantified as phase shift angle between oscillations in CBFV and ABP at a frequency of 6/min. A phase shift angle of 0 degrees indicates total absence of autoregulation, while 90 degrees can be gauged as optimal autoregulation. In addition, vasomotor reactivity of both MCAs to CO2 stimulation was assessed among patients and calculated as percent increase in CBFV per millimeter of mercury of increase in CO2. RESULTS: All normal subjects showed positive phase shift angles between CBFV and ABP (mean +/- SD, 70.5 +/- 29.8 degrees). OCD patients presented with significantly decreased phase shift angles for the MCA only on the pathological side (51.7 +/- 35.1 degrees; P < .05). Patients with AVM showed significantly reduced phase shift angles on both the affected side (26.8 +/- 13.5 degrees; P < .001) and the unaffected side (40.6 +/- 26.6 degrees; P < .01). In patients' groups, phase shift angle and vasomotor reactivity correlated significantly (r = .66; P < .001) after results from all MCAs were pooled. CONCLUSIONS: Results confirm the high-pass filter model of cerebral autoregulation: Normal subjects showed predicted positive phase shift angles between CBFV and ABP oscillations. Patients with expected autoregulatory disturbances showed significant decreases in phase shift angles. Close correlations existed between autoregulation and CO2-induced vasomotor reactivity.

Adult↗
PubMed1994

Magnetic motor evoked potentials (MEP) in diseases of the spinal cord.

Transcranial magnetic stimulation (TMS) is a non-invasive diagnostic method particularly suited to investigation of the long motor tracts. The clinical value of this method in many cortical and subcortical diseases has been well established, but comparable studies for most spinal cord diseases have still to be made. Forty patients in whom spinal cord disease was established by clinical examination, cerebrospinal fluid examination, and magnetic resonance imaging (MRI) were studied by means of somatosensory evoked potentials (SEP, median and tibial nerve stimulation) and magnetic motor evoked potentials (MEP, first dorsal interosseus and tibialis anterior muscle recordings after transcranial and spinal stimulation). The underlying pathology was neoplastic (n = 16), inflammatory (n = 15) or ischemic (n = 9). Clinical signs and symptoms ranged from slight sensory disturbances to complete paraplegia and had developed within minutes (ischemia) or over many years (benign neoplastic disease). The overall frequency of pathological SEP was slightly higher than that of MEP (78% vs 68%) which was statistically not significant (p > 0.05). This was also true for the subgroups, except for pure motor disorders, which gave the same yield for both methods. Decreased amplitudes or absence of MEP were more frequent in neoplastic than in inflammatory lesions (75% vs 33%, p < 0.05). In the latter, however, MEP more often occurred with increased latencies (40% vs 31%, p > 0.05, n.s.). Pathological SEP were found in 75% of patients presenting with pure motor abnormalities, while pathological MEP were found in 30% of patients with pure sensory disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Assessment of local sympathetic function in patients with erectile dysfunction.

Fifty men with erectile dysfunction (ED) were urologically investigated for autonomic deficit by evaluation of the sympathetic skin response at the penis. They were additionally subjected to thorough urological, vascular, psychiatric and neurological examinations, and well-established neurophysiological tests of the somatosensory, sympathetic, and parasympathetic function. Patients with clinical evidence of neurological deficit showed abnormal results (68%) in at least one test of the autonomic nervous system. The sympathetic skin response at the penis was absent in 11 cases (37%) with clinical evidence of neuronal aetiology of the erectile dysfunction and was normal in all cases with positive evidence of a psychiatric origin of erectile dysfunction and no clinical indication of a neuronal deficit. Moreover, the sympathetic skin response at the penis was abnormal in three cases with normal results in the other neurophysiological tests. The results emphasize that the local sympathetic skin response at the penis is a useful extension of autonomic testing in ED patients since this method tests local sympathetic pathways and is sometimes the only evidence for autonomic deficit. From a clinical viewpoint, the sympathetic skin response at the penis is a very simple and time-saving neurophysiological method suitable for clinical routine and also for the investigation of outpatients.

Adult↗
PubMed1992

Spontaneous vertebral artery dissection initially mimicking myocardial infarction.

BACKGROUND AND PURPOSE: Vertebral and carotid artery dissections may present with very different signs and symptoms, making early recognition difficult. However, diagnosis should be established as soon as possible to prevent unnecessary diagnostic investigations and to institute adequate treatment. CASE DESCRIPTION: A 46-year-old man presented with severe intermittent pain of his left upper arm and general discomfort. During extensive cardiological evaluation for suspected myocardial infarction, a severe brain stem syndrome occurred. Ultrasound Doppler studies detected vertebral artery dissection, which was confirmed by angiography. CONCLUSIONS: The unusual initial presentation of vertebral artery dissection delayed an early diagnosis and adequate treatment. Because noninvasive methods are available today, their applications are recommended in similarly uncharacteristic circumstances.

Aortic Dissection↗
PubMed1987

Pseudotumor cerebri: clinical and neuroradiological findings.

Pseudotumor cerebri (PTC) is a diagnosis per exclusionem applied to a condition of increased intracranial pressure in the absence of an intracranial infection, a space-occupying lesion, or hydrocephalus. Diagnostic criteria should include the evaluation of possibly disturbed cerebral venous outflow, which may result in similar clinical findings. Disturbed venous drainage should be separated from the syndrome of PTC because it represents a condition of well-defined origin and therapeutic regimen. Course and prognosis of PTC are not related to the increased intracranial pressure, the degree of papilledema, or to the duration of the disease. Functional cerebral disorders and EEG abnormalities are rare, indicating that brain tissue is not primarily affected. Correspondingly, computerized tomography (CT) scans with respect to the cerebrum are normal in about 90% of the cases; but enlarged optic nerve sheaths (46.7%) and empty sella (45.7%) are frequent findings on CT-scans. They most likely represent a direct consequence of long-term increased pressure within CSF spaces. This observation favors the assumption of disturbed CSF-pressure regulation either by increased production of CSF or its decreased rate of absorption. Brain edema (slit ventricles) as assessed by CT is a rare finding (11.4% of our cases). It may be a hint towards a different pathogenetic entity.

Adult↗
PubMed1986

Phorbol ester promotes growth of synaptic plasticity.

Iontophoretic application of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) to the intact rat hippocampus enhances potentiation produced by subsequent high frequency stimulation of the perforant path. The decay of the enhanced population spike amplitude recorded in the hilar dentate gyrus was prevented in animals receiving ejections of TPA, as compared to controls which decayed to baseline values within 2 h following high frequency stimulation. In fact, growth of the potentiated response was observed beginning at 45 min. Similar results were observed with the population excitatory postsynaptic potential slope, a measure of the synaptic response. Since tumour-promoting phorbol esters are known to translocate and activate protein kinase C (PKC) and PKC is translocated to the membrane following hippocampal potentiation, a role for membrane-associated PKC in the regulation of synaptic plasticity is suggested.

Action Potentials↗
PubMed1986

Superior sagittal sinus thrombosis: neuroradiological evaluation and clinical findings.

The spectrum of clinical signs in cases of superior sagittal sinus thrombosis includes not only focal neurological deficits, seizures and mental disturbances, but also symptoms which may lead to a diagnosis of pseudotumour cerebri (PTC). In 14 cases of angiographically (or autopsy) proven thrombosis of the superior sagittal or both lateral sinuses, the "empty triangle" sign on contrast CT examination was the most reliable sign, suggesting the diagnosis in 70%. Indirect CT signs (venous infarcts) were observed in all 8 patients with focal neurological signs, but appeared rather delayed in 3 cases. In contrast, patients with "benign" intracranial hypertension or PTC (6 cases) had normal unenhanced scans (4 cases) or showed slight diffuse brain oedema (2 cases). Magnetic resonance imaging was performed in 4 patients with findings suggestive of intravascular coagulation; however, due to the complexity of flow phenomena, further studies employing this new imaging technique will first have to be performed. Thus, angiography remains the best diagnostic tool and should not be delayed if there is a clinical suspicion of thrombosis.

Adolescent↗
PubMed1986

Leu-enkephalin impairs memory of an appetitive maze response in mice.

Leu-enkephalin (300 micrograms/kg) impaired memory of a Y-maze response in mice when the animals were trained to obtain food in one arm of the maze. The dose-response function was U-shaped, with neither 100 nor 600 micrograms/kg having any effect. Des-Tyr-Leu-enkephalin, a nonopioid peptide, had no effect at doses equimolar to the leu-enkephalin. Finally, the leu-enkephalin (300 micrograms/kg) was without effect if the drug injection was delayed 90 min. The results show that leu-enkephalin affects appetitive conditioning in much the same way as avoidance conditioning, a finding that suggests that leu-enkephalin may generally influence learning and memory.

Animals↗
PubMed1986

Human auditory steady state responses: effects of intensity and frequency.

Human auditory steady state responses were recorded in 41 normal subjects and 22 patients with hearing loss. The effect of intensity on the responses at different tonal frequencies was assessed using the sweep technique. The amplitude of the responses increases and the phase delay decreases with increasing intensity. Both the amplitude and the phase delay are smaller for high frequency tone bursts. Notched noise decreases the amplitude of the response by a factor of two but does not affect the phase of the responses. Thresholds were estimated in waking subjects using two techniques: intensity sweeps analyzed by linear regressions, and fixed intensities analyzed by Hotelling's T2 test. Frequency-specific thresholds obtained with notched noise were less variable and more accurate with the fixed intensity technique. In patients with sensorineural hearing loss the amplitude increased more with increasing intensity above threshold than in patients with conductive hearing loss.

Adult↗
PubMed1973

ATS in exposition.

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Computer-Assisted Instruction↗