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  • 1
    ISSN: 1573-2622
    Keywords: clinical electrophysiology ; electroretinogram ; pattern electroretinogram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The pattern electroretinogram (PERG) is a retinal response evoked by viewing an alternating checkerboard or grating. It receives clinical and research attention because it can provide information about inner retinal cells and the macula. However, clinicians may have trouble choosing between different techniques for recording the PERG that have been described in the literature. The International Society for Clinical Electrophysiology of Vision has prepared a standard for a basic PERG recording procedure to aid new users in obtaining reliable responses and to encourage more uniformity among existing users.
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  • 2
    ISSN: 1573-2622
    Keywords: glaucoma ; ocular hypertension ; pattern electroretinography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Diagnostic value of transient pattern electroretinogram (PERG), recorded by skin electrodes, was compared with Goldmann perimetry in cases of ocular hypertension and glaucoma. According to the assumption that the PERG mostly reflects activity of the retinal glanglion cells, and histological evidence that 30–50% atrophy of the retinal ganglion cells is necessary to cause defects in visual field, we wanted to assess if i) this method could be more sensitive in detecting early glaucomatous damage than routine Goldmann perimetry in eyes with normal or only borderline elevated intraocular pressure in the time of PERG recording (first group of patients), and ii) how the PERG amplitude corresponds to ganglion cell loss, expected in the eyes with already detectable initial glaucomatous visual field defects, according to Goldmann II/2 isopter, with normal or borderline elevated intraocular pressure in the time of PERG recording (second group). In the group with no visual field defects subnormal amplitude of the major positive component of the PERG, N1-P1, was detected in three of 30 eyes (10%), while in the group with initial visual field defects N1-P1 amplitude was subnormal in 6 of 11 eyes (54%). The amplitude of the major negative PERG component, P1-N2, was found normal in all eyes of the first group and subnormal in 5 eyes (45%) of the second group.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Documenta ophthalmologica 81 (1992), S. 253-259 
    ISSN: 1573-2622
    Keywords: Electrode ; electroretinography ; pattern electroretinogram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A new noncorneal electrode for clinical electroretinography was developed. It consists of a thin wire forming a loop modeled to fit into the lower conjunctival sac. Electrical contact is made with the scleral conjunctiva through an exposed portion of otherwise insulated wire. The recorded pattern electroretinograms are in the same amplitude range as if recorded by the gold foil electrode, while the flash electroretinograms with the new electrode are of about two-thirds the amplitude of corneal electrodes. The new electrode is more durable and hence less expensive than gold foil electrodes and can likewise be used without topical anesthetic. Cleaning is easy and effective. The electrode rarely causes discomfort and produces stable responses for at least 2 hours. The electrode aims to match stability of skin electrodes with sensitivity of fragile foil and fiber electrodes.
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  • 4
    ISSN: 1573-2622
    Keywords: Diurnal rhythm ; electroretinographic c-wave ; hereditary retinal degeneration ; melatonin ; retinal pigment epithelium ; Royal College of Surgeons rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The inability of retinal pigment epithelium to phagocytose shed photoreceptor disks is a cause of retinal degeneration in the Royal College of Surgeons rat; retinal pigment epithelial phagocytosis and disk shedding are regulated by the diurnal rhythm of retinal melatonin level. The diurnal rhythms of the electroretinogram (particularly that of the retinal pigment epithelial potential, the electroretinographic c-wave) and retinal melatonin content were thus investigated in Royal College of Surgeons rats from postnatal day 17 to 24, the period preceding retinal degeneration. The amplitudes of both the b- and c-waves of the electroretinogram fell significantly during the peak time of rod disk shedding and rose after the time of expected light off in the control and dystrophic rats. While the b-wave rhythms did not differ between the two strains, diurnal changes in the c-wave were significantly less distinct in the dystrophic rats than in controls. This difference may reflect lack of phagocytosis in dystrophic rats. Furthermore, the ERG c-wave was significantly larger and prolonged, and the retinal melatonin content higher, in dystrophic rats of this age group than in controls. It appears that retinal melatonin metabolism may play an important role in the maintenance of retinal pigment epithelial and photoreceptor function.
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  • 5
    ISSN: 1573-2622
    Keywords: pattern reversal VEP ; full-field W-shaped waveforms ; optic neuritis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We studied W-shaped waveforms that occurred in full-field responses to pattern large-field stimulation in patients who had optic neuritis. Affected eyes showed no absolute scotomata; visual acuity was normal at the time of recording. To evaluate the contribution of macular- and paramacular-derived components to the development of the W-shaped waveforms in the patients, half-field and central full-field stimulation was used. The responses were compared with those obtained with the use of experimental scotomata in healthy subjects. The W-shaped waveforms recorded in the patients closely resembled the responses observed in healthy subjects after the introduction of experimental scotomata. In all affected eyes, half-field stimulation showed absence of the ipsilateral P100 component or its interaction with the P135 component. Enhanced paramacular N105 and P135 components were seen over the contralateral hemisphere. Responses to central full-field stimulation were an attenuated and prolonged P100 in the majority of affected eyes. Results of our study showed that W-shaped waveforms in response to large full-field stimulation may reflect impaired function of macular fibers. These electrophysiologic findings, however, were not always associated with evidence of a central field defect demonstrated by Friedmann perimetry.
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  • 6
    ISSN: 1432-1041
    Keywords: Benserazide ; decarboxylase inhibition ; alpha-methyldopa ; essential hypertension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary In a single-blind study, the dopa-decarboxylase inhibitor benserazide (375 mg/day for 3 days and 750 mg/day for further 3 days) and a placebo were given orally in combination with individually effective doses of alpha-methyldopa (mean 1.5 g/day) to 3 hospitalized patients with essential hypertension. Alpha-methyldopa (α-MD) alone lowered blood pressure from 165/107 to 136/93 mm Hg (P〈0.05). Benserazide did not alter the hypotensive effect of α-MD, although the decarboxylation of α-MD was markedly reduced, as shown by the urinary excretion of alpha-methyldopamine (α-MDA). During administration of α-MD alone, the ratio α-MD/α-MDA in urine of the 3 patients was 8:1, 7:1 and 22:1, respectively. When benserazide 375 mg/day was added the ratio rose to 31:1, 31:1 and 35:1; the ratio was 37:1, 18:1 and 46:1 at the higher dose of inhibitor. In a double-blind crossover study the effect on blood pressure of 3 weeks of treatment with α-MD (mean 1.75 mg/day), benserazide (375 mg/day), placebo and their combinations were compared in 5 hypertensive subjects. Again, benserazide did not influence the antihypertensive action of α-MD. To study whether benserazide entered the CNS, a single oral dose of14C-benserazide of 125 mg was given to 2 patients who were to undergo diagnostic lumbar puncture. Two hours after intake of the labelled drug, when radioactivity in blood had reached a maximum, the concentration of radioactivity in spinal fluid was less than 1% of the plasma level. Thus, the antihypertensive action of α-MD was not influenced by oral doses of the decarboxylase inhibitor benserazide. The results suggest that benserazide in doses up to 750 mg/day does not affect central decarboxylation of α-MD and that this antihypertensive agent lowers blood pressure by a central action.
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  • 7
    ISSN: 1433-8580
    Keywords: Extracellular volume expansion ; cAMP ; cGMP ; Renal function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of graded extracellular fluid volume expansion (ECVE) on kidney content of cyclic 3′,5′-adenosine monophosphate (cAMP) and cyclic 3′,5′-guanosine monophosphate (cGMP) as well as on the renal electrolyte excretion was studied in 45 rats. ECVE was achieved by i.v. infusion of isotonic saline at rates of 2, 12, and 30 ml/h in intact and acutely parathyroidectomized (PTX) rats. The following results were obtained. 1. cAMP tissue levels during ECVE (2 ml/h) were 3.29 ± 0.38 pmol/mg dry weight and increased to 9.54 ± 1.1 (12 ml/h) and to 23.8 ± 1.9 pmol/mg dry weight (30 ml/h) in intact rats. The kidney in PTX rats did not respond with any changes of cAMP after ECVE. 2. cGMP tissue levels were 0.49 ± 0.12 pmol/mg dry weight at 2 ml/h and were only enhanced to 1.16 ± 0.22 pmol/mg dry weight (P 〈 0.001) during 30 ml/h in intact rats. In PTX rats no changes in cGMP tissue content could be found. 3. Phosphate excretion increased up to 363 ± 15 nmol/min · 100 g body weight during maximal ECVE and was significantly correlated to cAMP tissue levels (r = 0.89) in intact rats. The slight phosphaturia observed in PTX animals was not correlated with an increase of cAMP and was therefore thought to be PTH-independent. 4. Sodium and calcium excretion did not differ in intact and PTX rats during infusion of 2 and 12 ml/h. During maximal ECVE with 30 ml/h, however, sodium and calcium excretion were lower in PTX rats than in the intact animals. The decreased tubular load of these electrolytes in PTX animals due to a small drop in GFR and lower plasma calcium levels compared to intact animals could account, at least in part, for the reduced electrolyte excretion. 5. No consistent correlation was found between the tissue content of cyclic nucleotides and their urinary excretion rates. It is concluded that the cyclic nucleotides are not involved in the natriuretic response to ECVE. However, a small effect of PTH on the diuresis during maximal ECVE cannot be ruled out. The urinary excretion rates of cyclic nucleotides poorly reflect their corresponding tissue levels. The close correlation between phosphaturia and tissue cAMP levels in intact rats support the concept that parathyroid hormone induced phosphaturia is initiated by cAMP.
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  • 8
    ISSN: 1432-1912
    Keywords: cAMP ; cGMP ; Furosemide ; Diuretic action
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In Sprague Dawlwy rats left kidneys were quickly frozen 6–35 min after intravenous injection of furosemide (0.5, 5 and 50 mg/kg) using a clamp precooled with liquid nitrogen. Cyclic adenosine-3′:5′-monophosphate (cAMP) extracted from the tissue was assayed by a binding test with cAMP dependent protein kinase from beef heart and cyclic guanosine-3′:5′-monophosphate (cGMP) with a cGMP dependent protein kinase from lobster tail (humarus vulgaris). Glomerular filtration rate (as inulin clearance) and sodium excretion were measured. Within the first 8 min 0.5 mg/kg furosemide increased urine volume and sodium excretion 3-fold. cGMP levels rose two and a half-fold whereas the cAMP content was not significantly changed. Higher doses of 5 and 50 mg/kg furosemide increased urine volume and sodium excretion further. These doses now increased cAMP levels from 3.12±0.31 to 11.3±0.91 and 12.1±0.13 pmol/mg dry weight, respectively (P〈0.001). cGMP levels were elevated from 0.44 ±0.05 to 1.97±0.25 and 1.12±0.22 pmol/mg dry weight (P〈0.001). 26 min after the administration of the diuretic, tissue levels of both nucleotides had returned to control values. These data do not support the idea that the cAMP-adenylcyclase-system is involved in the mechanism of diuretic action of furosemide.
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  • 9
    ISSN: 1432-1912
    Keywords: Propranolol ; Antihypertensive Effect in Man ; Optical Isomers ; Plasma Levels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The antihypertensive actions of (+/-)-propranolol and of (+)-propranolol were compared in 10 patients with essential hypertension and in 1 patient with renovascular hypertension. The study was of double-blind crossover design. Bith, racemic propranolol and the (+)-isomer were ineffective in 4 hypertensives. In 7 patients, including the one with renovascular hypertension, (+/-)-propranolol significantly decreased supine systolic and diastolic as well as standing systolic blood pressure. None of these parameters was altered by identical doses of (+)-propranolol. Propranolol plasma levels measured during treatment with racemic propranolol did not differ from the concentrations determined during the (+)-propranolol period. The data indicate that the hypotensive effect of propranolol in man is due to β-receptor blockade.
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  • 10
    ISSN: 1432-1440
    Keywords: Plasmakatecholamine ; Dopamin-β-Hydroxylase ; Essentielle Hypertonie ; Körperliche Belastung ; Plasma catecholamines ; Dopamine-β-hydroxylase ; Essential hypertension ; Physical exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary In 8 normotensive subjects and in 8 patients with essential hypertension total catecholamine content and dopamine-β-hydroxylase (DBH) activity in plasma were measured at rest and during physical exercise. Catecholamine levels at rest were significantly higher in the hypertensive than in the normotensive persons whereas the 2 groups of subjects did not differ in DBH activity at rest. At a work load of 150 watts there was a more pronounced increase of the catecholamine concentrations and of the DBH activity in the hypertensive patients than in the normotensives. One may conclude from the data that there is an increased sympathetic nerve activity in patients with essential hypertension.
    Notes: Zusammenfassung Bei 8 Normotonikern sowie bei 8 Patienten mit essentieller Hypertonie wurden die Konzentrationen der Gesamtkatecholamine und die Aktivität der Dopamin-β-Hydroxylase (DBH) im Plasma unter Ruhebedingungen und während körperlicher Belastung gemessen. Bei den Hypertonikern waren die Ruhewerte der Katecholamine signifikant höher als bei den Normotonikern, während die DBH-Aktivität unter diesen Bedingungen bei beiden Gruppen gleich war. Bei einer Ergometerbelastung von 150 Watt stiegen die Katecholaminspiegel und die DHB-Aktivität bei den Hochdruckkranken stärker an als bei den Probanden mit normalem Blutdruck. Aus den Untersuchungsergebnissen kann man schließen, daß bei Patienten mit essentieller Hypertonie eine erhöhte Aktivität sympathischer Nerven besteht.
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