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Biomedical subjects

I Keller

Publications and source records attributed to I Keller.

At least 37 records · Page 2Linked to original sources
PubMed1995

Formoguanamine-induced inhibition of deprivation myopia in chick is accompanied by choroidal thinning while retinal function is retained.

Twenty hatchling chickens were injected intravitreally every 4 days from day 2 to day 16 with dimethyl sulphoxide (DS) in one eye and DS or formoguanamine dissolved in DS (FG.DS) with or without occlusion in the other (FG.DS.MD, DS.MD, FG.DS). At day 16, the FG.DS.MD eyes failed to show the high refractive myopia and showed less axial elongation than that developed by the DS.MD eyes. Electroretinograms indicated that at the dosage used, FG.DS does not eliminate phototransduction. Light microscopy showed choroidal and retinal thinning in DS.MD and FG.DS.MD eyes but less than in FG.DS eyes, suggesting that change in choroidal thickness is unlikely to be the primary cause of form deprivation myopia.

Animals↗
PubMed1995

Selective impairment of auditory attention following closed head injuries or right cerebrovascular accidents.

According to clinical experience a frequent consequence of head injury is an impairment of auditory attention. We investigated the possibility that patients with either closed head injuries (CHI), or cerebrovascular accidents (CVA) of the right hemisphere, would be impaired by comparison to healthy subjects on an objective test of auditory attention. We used an experimental paradigm that consisted of four subtests which comprised strings of auditory digits heard either diotically or dichotically, at either fast or slow presentation rates, respectively. Omission and commission errors were scored for each subtest and combined by an index of errors. The results showed that CHI patients were significantly impaired initially by the fast stimulus presentation conditions, whereas CVA patients made significantly more errors on the dichotic subtests independent of the speed of presentation. It is proposed that the observed selective attention deficits of these patients were due to differential disruptions of an interactive cortical network incorporating prefrontal, anterior cingulate, and temporoparietal structures of the right hemisphere. Statistically significant correlations between the error index scores and subjectively perceived attention deficits suggested that the auditory attention task measured clinically relevant aspects of attention.

Adult↗
PubMed1995

Radiology on the information superhighway.

PURPOSE: To explore the potential for the information superhighway to provide radiologists with new opportunities. MATERIALS AND METHODS: The Internet was used as the communication and distribution medium. MOSAIC, a graphical interface, provided access for clients, and a computer was used to serve text, images, sound, and cine onto the Internet. RESULTS: The system can be used to send reports and images to referring physicians or consulting radiologists; to provide a large database that is constantly available; to provide an increasing collection of teaching files; and to distribute interactive, multimedia teaching tools that can be used on any computer system. The use of the MOSAIC interface facilitates interaction, which allows users with limited computer experience to access the system. CONCLUSION: The Internet can dramatically expand the ways radiologists interact with their colleagues. These preliminary results indicate that there will be great challenges and opportunities for improving care and teaching in the future.

Computer Communication Networks↗
PubMed1992

Determination of maleic hydrazide residues in cured tobacco by gas chromatography.

A rapid and sensitive method for measuring maleic hydrazide (6-hydroxy-2H-pyridazin-3-one) residues in cured tobacco is described. A mixture of free and bound maleic hydrazide is extracted with hydrochloric acid in which maleic hydrazide glycoside is simultaneously hydrolysed. The free maleic hydrazide obtained is methylated using dimethyl sulphate and the derivative is partitioned into chloroform and determined by capillary gas chromatography using a nitrogen-phosphorus detector. The limit of detection of maleic hydrazide is 5 ppm.

Chromatography, Gas↗
PubMed1992

Measurement of converting enzyme activity by antibody-trapping of generated angiotensin II. Comparison with two other methods.

Activity of the angiotensin converting enzyme (ACE) is usually measured in vitro by estimation of products cleaved by the enzyme from synthetic substrates. These substrates have affinities for ACE different from the natural substrate angiotensin I, and insensitive detection systems necessitate millimolar substrate concentrations while physiological angiotensin I concentrations are in the picomolar range. A new assay for ACE activity measurement was developed which reliably quantitates femtomoles of generated angiotensin II in plasma from angiotensin I added at a 17 pmol/mL concentration. The production of high affinity monoclonal antibodies against angiotensin II (Kd = 7 x 10(-11) mol/L) allowed a quantitative trapping (and thus protection from degrading enzymes) of angiotensin II generated during the incubation step and subsequent radioimmunoassay by simple dilution with labelled angiotensin II. Using 40 microL plasma, the detection limit was 20 fmol/mL/min. Normal human plasma has an ACE activity of 335 +/- 83 fmol/mL/min (mean +/- SD). Precision was characterized by coefficients of variation of less than or equal to 11% both within-assay and between-assays. Accuracy of the new method was established by comparing ACE activity with the ratio of plasma angiotensin II/angiotensin I in plasma obtained from normal volunteers 0.5 to 24 h after oral administration of 20 mg enalapril. The percentage of ACE inhibition indicated by both methods was almost identical (r = 0.93, n = 60, P less than .001). Since the latter ratio appears to reflect in vivo ACE activity, these results indicate that accurate measurement in vitro of ACE activity in vivo has been achieved.

Administration, Oral↗
PubMed1991

[Sensory information processing during general anesthesia-- acoustic-evoked 30-40 Hz oscillations and intraoperative wakefulness during cesarean section].

Neuropsychological and neurophysiological investigations indicate that the underlying framework of adequate sensory information processing is a 30-40 Hz oscillatory brain mechanism, which also can be observed in mid-latency auditory evoked potentials (MLA-EP). Since high incidence of stimuli perception and wakefulness is a phenomenon during Caesarean section under general anaesthesia it was studied if auditory evoked 30-40 Hz oscillation correlate with intraoperative wakefulness during this surgical procedure. Following informed consent, 21 patients were selected for elective Caesarean section. Anaesthesia was induced with thiopentone (5 mg/kg b.w. i.v.) and maintained with thiopentone bolus injection (1-2 mg/kg b.w.i.v). and O2/N2O 1:1 according to clinical signs of adequate anaesthesia. After delivery, a balanced anaesthetic technique using fentanyl, enflurane and N2O in O2 1:1 was employed. Clinical signs of intraoperative wakefulness were spontaneous movements of the limbs, mimics, eye-opening, wakefulness after auditory stimulation (tape A: crying baby, tape B: classical music), one hour and 24 hours postoperatively reported dreams, hallucinations and detailed reports about intraoperative events. Auditory evoked potentials were recorded on-line before and during general anaesthesia, during the entire surgical procedure. Latencies of the peaks V, Na, Pa were measured. Employing Fast-Fourier transformation analysis, corresponding power spectra were calculated to analyse energy portions of AEP's frequency components. Spontaneous motoric movements occurred in 60% of the patients and did not correlate with heart rate, blood pressure or other clinical signs of inadequate anaesthesia. Provoked motoric reactions were 4 times as often after presentation of tape A as after tape B.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1991

[The effect of thiopental on mid-latency auditory evoked potentials and their frequency analysis].

The effect of Thiopentone on mid-latency auditory evoked potentials has not yet been examined sufficiently. Therefore, mid-latency auditory evoked potentials during induction of general anaesthesia with thiopentone were studied. Following informed consent in 10 patients scheduled for elective surgery, anaesthesia was induced with thiopentone (5 mg/kg b.w. i.v.). Assisted ventilation via face mask with 100% O2 was performed until the first purposeful movement of the limbs appeared. Then a second bolus of thiopentone (2 mg/kg b.w. i.v.) was given and general anaesthesia was maintained according to anaesthesiological and operative necessities. Auditory evoked potentials were recorded in the awake and on-line when thiopentone was injected up to 9 min after the onset of general anaesthesia. Latencies of the peaks V, Na, Pa were measured. Using Fast-Fourier-Transform-Analysis, corresponding power spectra were calculated to analyse energy portions of the AEP frequency components. In the awake state peak latencies were in the normal range. Corresponding power spectra indicated energy maxima in the 30-40 Hz frequency range. After induction of general anaesthesia an increase in latencies of the peaks Na, Pa could be observed. The energy in the 30-40 Hz range became suppressed, the AEP energy maxima shifted to the low frequency range. These effects were observable until 3 min after injection. When the first purposeful movement of a limb occurred, Na, Pa latencies returned to normal values and most part of the AEP-energy was in the 30-40 Hz range as in the awake.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

The comparative evaluation of three-dimensional magnetic resonance for carotid artery disease.

Conventional angiography is the current standard for the evaluation of carotid artery disease. The excellent resolution of this invasive study is offset by the potential for contrast-related, embolic, and puncture site complications. Three-dimensional magnetic resonance angiography may offer a noninvasive diagnostic alternative. We examined this possibility by performing both conventional angiography and three-dimensional magnetic resonance angiography in 13 patients. Cervical duplex scans were also obtained in these patients. Contiguous transverse cervical magnetic resonance images were acquired in a 1.5 tesla magnet, by use of a posterior neck coil and a gradient echo pulse sequence. These "raw" data were transferred to a real-time workstation where three-dimensional cervical arterial images were reformatted, magnified, and examined from multiple angles. Total study time from patient positioning to image generation was approximately 30 minutes. In all patients, on three-dimensional magnetic resonance angiography the common, external, and internal carotid arteries and distal vertebral arteries were easily discernable and correctly identified as patent, stenotic, or occluded. Three-dimensional magnetic resonance angiography was not accurate in detecting carotid ulcers. The degree of internal carotid artery stenosis measured from the three-dimensional magnetic resonance angiography studies correlated well with the internal carotid artery stenosis measured with conventional angiography (r = 0.866, r2 = 75.1%, p = less than or equal to 0.0001). This recent technologic advance represents significant progress toward achieving the goal of completely noninvasive vascular assessment in this patient population.

Aged↗
PubMed1991

Sensory information processing during general anaesthesia: effect of isoflurane on auditory evoked neuronal oscillations.

There is evidence from neuropsychological and psychophysical measurements that sensory information is processed in discrete time segments. The segmentation process may be described as neuronal oscillation at a frequency of 30-40 Hz. Stimulus-induced neuronal oscillations of this frequency are found in the middle latency range of the auditory evoked potential (AEP). We have studied the effect of different end-tidal concentrations of isoflurane on auditory evoked 30-40 Hz neuronal oscillations. We studied 13 patients undergoing intra-abdominal urological and gynaecological procedures. AEP were recorded in the awake state and during end-expiratory steady state isoflurane concentrations of 0.3, 0.6 and 1.2 vol%. These incremental doses of isoflurane caused a stepwise decrease in frequency of oscillations. The decrease in oscillation frequency and sometimes the disappearance of oscillatory components may be interpreted as suppression of sensory information processing. The measurement of auditory evoked neuronal oscillations in the AEP appears to be a promising tool to monitor both sensory information processing capacity and depth of anaesthesia.

Adult↗
PubMed1991

Use of immunoglobulin heavy-chain and light-chain measurements in a multicenter trial to investigate monoclonal components: I. Detection.

We assessed the combined use of serum protein electrophoresis (SPE) and nephelometric measurement of immunoglobulin heavy- and light-chain components for detecting serum monoclonal immunoglobulins (monoclonal components, MC) in 4788 unselected samples from 4173 patients. MC were detected in 514 samples from 390 patients. In 356 these were detected by SPE; the other 34 had a normal SPE pattern but an abnormal kappa:lambda light-chain ratio (KLR). Only 208 of the 356 (58%) samples with bands by SPE had abnormal KLRs. Samples with MC concentrations greater than 5 g/L had a higher proportion of abnormal KLRs (75%) than those with concentrations less than 5 g/L (42%). The KLR was abnormal in 13% of samples in which no MC were visible by SPE or immunofixation electrophoresis (IFE). Compared with quantitative measurements of immunoglobulin heavy and light chains, high-quality SPE remains the method of choice for the detection of MC. Quantitative methods, however, are able to detect additional MC, especially those containing free light chains, and in the absence of SPE and IFE will detect about 75% of MC present at greater than 5 g/L.

Antibodies, Monoclonal↗
PubMed1991

Use of immunoglobulin heavy-chain and light-chain measurements in a multicenter trial to investigate monoclonal components: II. Classification by use of computer-based algorithms.

We describe a computer algorithm for classifying serum monoclonal proteins (MC) based on serum protein electrophoresis (SPE) and the automated measurement of kappa and lambda light chains and IgG, IgA, and IgM. We developed the algorithm by using a large database of unselected samples containing MC collected in a multicenter study. The performance of the algorithm was optimized by using iterative computational procedures and was tested on both the development database and on an independent set of MC-containing samples. With the development database, the algorithm correctly classified 50% and misassigned 2.5% of the MC. Where the MC were present in concentrations greater than 10 g/L, the rate of successful classification increased to 72% with 3% misclassification. When the algorithm was tested on a group of 101 MC-containing samples from an independent source, 67% were correctly classified and 8% misclassified, half of the latter being unusual IgD myelomas. We discuss the scope for the application of the algorithm in routine laboratory practice involving personal computer software.

Algorithms↗
PubMed1991

[Acoustic evoked potentials of medium latency and intraoperative wakefulness during anesthesia maintenance using propofol, isoflurane and flunitrazepam/fentanyl].

Auditory evoked potentials have been used as an indicator of awareness. During combined local and general anesthesia clinical signs of adequate anesthesia are difficult to evaluate. In the present study we combined peridural analgesia with three techniques of general anesthesia. Intraoperative wakefulness was documented and correlated with cardiocirculatory parameters as well as with mid-latency auditory evoked potentials (MLAEP). METHODS. After institutional approval and informed consent 30 patients undergoing elective laparotomy were studied as follows: first, continuous peridural analgesia was instituted in all patients to block painful sensation of surgical stimuli and the anesthetic level was maintained at T5. Then general anesthesia was induced with propofol 2.5 mg/kg i.v. (group I, n = 10), thiopental 5 mg/kg i.v. (group II, n = 10), or etomidate 0.2 mg/kg i.v. (group III, n = 10) and maintained with propofol 3-5 mg/kg per hour i.v. (group I), isoflurane 0.4-0.8 vol.-% (group II), or flunitrazepam 0.005-0.01 mg/kg i.v. and fentanyl 0.0025-0.005 mg/kg i.v. bolus injections every 20-30 min (group III). Heart rate and arterial pressure were registered continuously. Purposeful movements of the limbs, eye-opening, or other movements as well as coughing were documented as signs of intraoperative wakefulness. AEP were recorded in the awake state, after induction, and during maintenance of general anesthesia. Latencies of the peaks V, Na, and Pa were measured. By fast-Fourier transformation corresponding power-spectra were calculated to analyze the energy content of the AEP frequency components. RESULTS. Intraoperative wakefulness occurred statistically significantly more often in the patients of group III than in those of groups I and II. There was no correlation between wakefulness and cardiocirculatory parameters. Latencies of peaks V, Na, and Pa in the awake patients were in the normal range; the corresponding power-spectra had their major energy content in the 30-40-Hz range. After induction of general anesthesia with propofol, thiopentone, and etomidate as well as during maintenance of general anesthesia with propofol and isoflurane peak latencies of Na and Pa increased, frequencies in the 30-40 Hz range became suppressed, and MLAEP energy maxima shifted to the low-frequency range. In contrast, during maintenance of general anesthesia with flunitrazepam/fentanyl peak latencies of Na and Pa returned to awake values and frequencies in the range of 30 Hz regained energy dominance in the corresponding power-spectra. CONCLUSIONS. The maintenance of MLAEP and the primary cortical complex Na/Pa correlates with the incidence of motor signs of wakefulness. During the combination of regional and general anesthesia, isoflurane and propofol seem to provide better suppression of intraoperative wakefulness than bolus injections of flunitrazepam/fentanyl.

Adult↗
PubMed1990

Readiness potentials preceding spontaneous motor acts: voluntary vs. involuntary control.

Libet et al. (1983) developed a method to compare the onset time of a readiness potential (RP) with the onset time of the corresponding intention to perform a spontaneous voluntary motor act. In relation to the onset of the RP, the time of conscious intention to move followed 350 msec later. From these results Libet (1985) concluded that the cerebral initiation of a spontaneous voluntary act begins unconsciously. We investigated the alternative interpretation that with the instruction to pay attention to feelings of 'wanting to move,' automatic and normally unconscious motor acts might have been brought to a level of conscious awareness. Therefore we conducted 3 kinds of experiment. In the first, RPs were measured from subjects performing unconscious movements. The second experiment was a replication of Libet's study while the third was a resting condition in which subjects looked for intentions to move introspectively. The results showed that RPs beginning approximately 500 msec before movement onset can be obtained with unconsciously as well as consciously performed spontaneous motor acts. The different scalp distributions of the two types of RP indicate that unconscious movements can be attributed to the activation of a contralateral process (lateral premotor system (LPS), primary motor cortex), whereas voluntary spontaneous motor acts seemed to be predominated by the medial premotor system (MPS). It is proposed that in the Libet situation focused attention on internal events led to the conscious detection of a normally unconscious process. This resulted in the activation of the MPS, especially the supplementary motor area (SMA), which released the starting signal for the execution of the motor act. We believe that the activation of the SMA and the urge to move occurred at the same time.

Adult↗
PubMed1990

An immunochemical evaluation for the identification and typing of monoclonal proteins.

Using automated measurements of kappa (kappa) and lambda (lambda) light chain and IgG, IgA and IgM concentrations we assessed the ability of the kappa/lambda ratio and the heavy/light chain ratio to identify and type monoclonal components which had been previously identified by serum protein electrophoresis and immunoelectrophoresis. We examined 1151 samples, of which 277 contained monoclonal components; 90% of the monoclonal proteins could be identified by this approach, of which 95% were correctly typed. In addition 19 of 874 samples without monoclonal components showed an abnormal kappa/lambda ratio. We assessed the ability of the immunochemical evaluation to calculate monoclonal component concentration and then compared the results to the scanning densitometry of serum protein electrophoresis.

Blood Protein Electrophoresis↗
PubMed1990

Analysis of oscillatory components in perioperative AEP-recordings: a nonparametric procedure for frequency measurement.

Auditory evoked potentials (AEPs) were recorded in 15 patients scheduled for minor gynecological procedures. The suppression of a middle latency oscillation about 40 Hz was observed during 2 minutes after injection of the anesthetic agent propofol. The decrease in oscillation frequency during anesthetic induction was evaluated with a fast Fourier transformation (FFT) and a rank-correlation procedure (RCP). With AEPs having a short epoch of 100 ms the frequency resolution of the RCP was better than the frequency resolution of the FFT. The rank-correlation function of the RCP indicates an initial drop of oscillation frequency from 44 Hz to 37 Hz during 1 minute after anesthetic induction. During the second minute after the infusion of propofol, the oscillation frequency decreases from 37 Hz to 19 Hz. It is suggested that the suppression of neuronal oscillations in the AEP represents a loss of sensory information processing. The measurement of middle latency oscillations in the AEP is proposed to be a promising indicator for the intraoperative stage of anesthesia.

Adult↗
PubMed1990

[Middle-latency auditory evoked potentials during high-dose opioid analgesia].

Neuropsychological and neurophysiological investigations indicate that a 30-40 Hz oscillatory brain mechanism is necessary for the adequate uptake and processing of elementary successive sensory events. An oscillatory component of that particular frequency range can be observed in the mid-latency auditory evoked potential (MLAEP). It is suppressed under non-specific anesthetic agents (agents not acting on specific structures of the brain or receptors). Opioids produce analgesia, sedation, and are also used for induction and maintenance of general anesthesia. The effect of opioids on MLAEP has not yet been examined sufficiently. Because intraoperative wakefulness and awareness is not rarely observed under high-dose opioid analgesia, the effect of general anesthesia with fentanyl on MLAEP and auditory evoked neuronal 30-40 Hz oscillation was studied. Following informed consent in 20 patients scheduled for elective surgery, anesthesia was induced with fentanyl 0.01-0.02 mg/kg i.v. Auditory evoked potentials (AEP) were recorded before and 5 min after the start of general anesthesia over the vertex (positive) and mastoids on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL with a frequency of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet Co.), 1000 successive stimuli were averaged over a 100-ms post-stimulus period and analyzed off-line. Latencies of the peaks V, Na, and Pa were measured. By Fast-Fourier Transform-analysis corresponding power spectra were calculated to analyze energy portions of the AEP frequency components. In the awake state AEP showed an oscillatory component between 20- and 100-ms post-stimulus latency. Corresponding power spectra indicated a dominant 30-40 Hz frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

[Mid-latency auditory evoked potentials during induction of intravenous anesthesia using midazolam, diazepam and flunitrazepam].

Since intraoperative awareness is not infrequently observed under balanced anaesthetic regimens employing benzodiazepines for suppression of consciousness, we studied the effect of intravenous induction of general anaesthesia using the benzodiazepines midazolam, diazepam and flunitrazepam on mid-latency auditory evoked potentials and auditory evoked neuronal 30-40 Hz oscillation. Following informed consent in 30 patients scheduled for minor gynaecological procedures, anaesthesia was induced with midazolam (0.2-0.3 mg/kg b.w. i.v., group I n = 10), diazepam (0.3-0,4 mg/kg b.w., i.v., group II n = 10) or flunitrazepam (0.03-0.04 mg/kg b.w., i.v., group III n = 10). Auditory evoked potentials were recorded before, during and after induction of general anaesthesia on vertex (positive) and mastoides on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL with a frequency of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet), 1000 successive stimuli were averaged over a 100 ms poststimulus period and analysed off-line. Latencies of the peak V, Na, Pa were measured. By means of Fast-Fourier transformation-analysis corresponding power spectra were calculated to analyse energy portions of the AEP frequency components. In the awake state AEP showed an oscillatory component between 20 and 100 ms poststimulus latency. Corresponding power spectra indicated a predominant 30-40 Hz frequency. After induction of general anaesthesia using midazolam, diazepam and flunitrazepam, there was no increase in latencies of the peaks V, Na, Pa, but only a small decrease in amplitudes Na/Pa without statistical significance. The auditory evoked mid-latency neuronal oscillation persisted under induction of general anaesthesia with midazolam, diazepam, flunitrazepam.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗