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Biomedical subjects

W Ritter

Publications and source records attributed to W Ritter.

At least 19 recordsLinked to original sources
PubMed2001

Spatiotemporal maturation of the central and lateral N1 components to tones.

This paper examines maturational changes in the spatiotemporal features of central and lateral N1 components of the auditory evoked potentials (AEPs) to tone stimuli presented with a long stimulus onset asyncrony (SOA; 4200 ms) using the scalp current density (SCD) technique. A group of typically developing children ranging from 6 to 12 years of age and a group of adults were studied. Recently studies have begun to explore the topography of these components in children. These studies, however, often used rapidly presented stimuli and did not elicit observable central N1s in the younger children. Our stimuli elicited both central and lateral N1s. Peak latencies of both components decreased with age. Peak amplitude also decreased with age for the lateral N1 but not for the central N1. Consequently, the difference between the lateral N1 and the central N1 amplitudes (or the ratio of lateral N1 amplitude to central N1 amplitude) also decreased with age, dramatically altering the morphology of the elicited AEP waveforms. Topography of the lateral N1 did not change with age. The location of maximal activation for the central N1 appeared to move more medially with age but this 'apparent' movement is probably due to the decreasing impact of the partially overlapping lateral N1 component whose amplitude is significantly smaller in adults than in children.

Acoustic Stimulation↗
PubMed2001

An event-related potential evaluation of involuntary attentional shifts in young and older adults.

Involuntary shifts in attention to irrelevant stimuli were studied in elderly and young volunteers during a dichotic-listening task. Event-related potentials and behavioral measures were recorded. Volunteers heard pairs of tones presented with 2 different stimulus onset asynchronies (SOAs). To-be-ignored tones were presented to the left ear, followed by to-be-attended tones to the right ear. Left-ear tones were a frequent standard (700 Hz) and an infrequent small (650 Hz) and large (500 Hz) deviant. Right-ear tones (1500 Hz) were presented with 2 equiprobable intensities. Volunteers responded to the lower intensity stimulus. Behavioral performance was impaired at the short SOA when to-be-ignored large deviants preceded to-be-attended targets, but more so for the elderly volunteers. Large deviants also elicited the mismatch negativity (MMN) and P3a for both age groups. It was concluded that the more impaired behavioral performance observed for the elderly was due to greater sensitivity to output from the MMN system by a frontal lobe system responsible for the maintenance of attentional focus.

Adult↗
PubMed2001

[Endovascular therapy of renal artery stenosis: technical results with the Palmaz-Corinthian stent].

OBJECTIVE: To evaluate the technical performance and delivery characteristics of the Palmaz-Corinthian stent for endovascular therapy of atherosclerotic renovascular disease. METHODS: 61 patients underwent implantation of 76 Palmaz-Corinthian (PC) stents in 72 arteries. 50 original PC and 26 PC stents with the modified IQ-design were employed. The indications comprised primary stenting of ostial (n = 49) or truncal (n = 1) stenosis or occlusion (n = 3), and selective stenting following complicated (dissection, n = 4) or unsuccessful (n = 8) angioplasty. The remaining stents were placed in patients with recurrent stenosis (n = 5) or acute aortic dissection (n = 2) involving the renal artery. Mean severity and length of stenosis were 81.3% and 9.8 mm, respectively. 39 lesions were rated eccentric or calcified. Data on technical success, complication rate, delivery characteristics and ease of placement compared to standard renal stents were retrieved from a prospective multicenter registry. RESULTS: Stent delivery was successful in all patients, major complications were not reported. Stent placement was suboptimal in 7 of 72 cases: 4 stents were located too distally in the renal artery, necessitating proximal coaxial overstenting in 2 cases. The distal part of the stenosis was incompletely covered and the orifice of a segmental branch inappropriately overstented in one case each. One stent was dislodged from the balloon, resulting in stent protrusion in the aortic lumen. Significant residual stenosis after stenting was not observed. Overall stent deliverability, trackability and potential repositioning inside the stenosis were rated positive, radio-opacity was rated superior for the IQ design. CONCLUSION: Technical performance and delivery characteristics of the Palmaz-Corinthian stent have been significantly improved compared to the Palmaz design, allowing mostly correct placement in renal artery stenoses with a low complication rate.

Angiography, Digital Subtraction↗
PubMed2001

The detection of constancy amidst change in children: a dissociation of preattentive and intentional processing.

This study examined whether 7-9-year-old children preattentively build memories of constancy for individual stimulus features, and if these representations are affected by variability of other stimulus features. This was achieved by looking at the mismatch negativity (MMN) event-related potential to a duration deviant occurring in a stimulus environment in which one or two other features constantly changed. Performance data were also collected, to look at the correspondence between the effects of this manipulation on preattentive and intentional deviance detection. MMN data indicated that the children built a preattentive feature-based memory of constancy that was not affected by the number of varying features. In contrast, intentional deviance detection was considerably impaired by the introduction of feature variability. This dissociation is at variance with previous studies that usually report close association between MMN and behavior.

Acoustic Stimulation↗
PubMed2001

Sacbrood virus of the honeybee (Apis mellifera): rapid identification and phylogenetic analysis using reverse transcription-PCR.

Sacbrood virus (SBV) infects larvae of the honeybee (Apis mellifera), resulting in failure to pupate and death. Until now, identification of viruses in honeybee infections has been based on traditional methods such as electron microscopy, immunodiffusion, and enzyme-linked immunosorbent assay. Culture cannot be used because no honeybee cell lines are available. These techniques are low in sensitivity and specificity. However, the complete nucleotide sequence of SBV has recently been determined, and with these data, we now report a reverse transcription-PCR (RT-PCR) test for the direct, rapid, and sensitive detection of these viruses. RT-PCR was used to target five different areas of the SBV genome using infected honeybees and larvae originating from geographically distinct regions. The RT-PCR assay proved to be a rapid, specific, and sensitive diagnostic tool for the direct detection of SBV nucleic acid in samples of infected honeybees and brood regardless of geographic origin. The amplification products were sequenced, and phylogenetic analysis suggested the existence of at least three distinct genotypes of SBV.

Amino Acid Sequence↗
PubMed2001

The effect of perceptual grouping on the mismatch negativity.

The mismatch negativity (MMN) was used as a probe to evaluate changes, with age, of transient auditory memory. Subjects were 16 young (M = 23 years) and 16 old (M = 72 years) people. Standard auditory stimuli were presented in trains of eight tones (1000 Hz) with either a I-s or 8-s intertrain interval (ITI). Occasionally, the first stimulus of a train was replaced with a 1200 Hz tone (deviant). The MMN was recorded while subjects watched a silent movie and ignored the sounds. Both groups of subjects showed an MMN response to deviant stimuli under the 1-s ITI condition, but MMNs were only seen for some subjects under the 8-s ITI condition. After MMN recording, subjects performed a discrimination task to the tones used for recording MMNs. Accuracy for both groups was near 100% at both ITIs. These results suggest that generation of MMN is a function of the perceptual grouping of the acoustical stimuli and that the integrity of perceptual grouping may be maintained with increased age.

Adult↗
PubMed2000

Effect of frequency separation and stimulus rate on the mismatch negativity: an examination of the issue of refractoriness in humans.

Refractoriness of the generators of the mismatch negativity (MMN) was examined in two experiments in which two deviant tones occurred in a row. In Experiment 1, the size of the MMN elicited by the first deviant was manipulated by using deviants that were close to or far from the standard in frequency. In Experiment 2, the time between two identical deviants was varied. It was found that neither the size of the MMN elicited by the first deviant, nor the time between two deviants, affected the amplitude of the MMN elicited by the second deviant. It was concluded that refractoriness played no role in the amplitude of the MMN for the parameters used.

Adult↗
PubMed2000

Evidence that the mismatch negativity system works on the basis of objects.

The purpose of this study was to determine whether the system that underlies the mismatch negativity (MMN) of event-related potentials would operate on the basis of objects if stimuli were delivered in such a way as to create the impression of two objects. To this end, tones were alternated between ears with one combination of features for each ear. Deviant tones, which differed from the standard tones of both ears, were delivered separately to each ear. The deviants elicited MMNs only with respect to the standards of the ear to which they were delivered. The data indicate that the MMN system operated on the basis of objects and that the integration of objects occurs preattentively in the auditory system.

Acoustic Stimulation↗
PubMed2000

The development of auditory attention in children.

In this paper we review the development of four components of auditory attention: arousal, orienting, selective attention and sustained attention. We focus especially on the processes responsible for the selection of specific stimuli for further processing because these are essential for learning and development. Although much work still needs to be done, there is evidence of developmental change in some of the components of attention, especially early in infancy. Later developmental improvements seem to be primarily attributable to higher cognitive processes, such as motivation, strategy development and implementation, and voluntary direction and regulation of attention.

Arousal↗
PubMed2000

Associated deficits in mismatch negativity generation and tone matching in schizophrenia.

OBJECTIVE: Schizophrenia is associated with deficits in mismatch negativity (MMN) generation and in the ability to match two tones following brief delay. Both deficits reflect impaired early cortical processing of auditory information. However, the relationship between deficits in MMN generation and tone matching performance in schizophrenia has not been established. METHODS: MMN and tone matching performance was evaluated in 12 schizophrenic subjects and 12 similar aged controls. A pitch separation known to produce non-ceiling performance in patients (5% Deltaf) was used. Narrow band filtering of MMN data was used to enhance signal-to-noise ratio. RESULTS: Schizophrenic subjects showed impairments in both MMN generation and tone matching performance. The two deficits were significantly correlated across subjects. In addition, decreased MMN amplitude and poorer tone matching performance correlated with increased severity of negative symptoms. CONCLUSIONS: These findings support the concept that similar neurophysiological mechanisms underlie MMN and tone matching deficits in schizophrenia. Further, they indicate that increased sensitivity to environmental change may be related to social withdrawal and other negative symptoms in schizophrenia.

Acoustic Stimulation↗
PubMed2000

[3D vascular imaging with power mode in planning and controlling percutaneously implanted abdominal aortic stent grafts].

PURPOSE: Evaluation of the reliability of vascular ultrasound with power mode and 3D-power mode for preinterventional planning before endovascular treatment of abdominal aortic aneurysms and postoperative follow-up after endografting. MATERIAL AND METHOD: A new real-time 3D technique with power mode flow imaging was used in a prospective study of 75 patients with infrarenal aortic aneurysms, in 25 cases before and in 50 cases after stentgraft implantation. The results of vascular ultrasound with color-coded duplex sonography (CCDS), power mode and 3D power mode were compared with CTA and DSA in all cases. RESULTS: Only the length and diameter of the aneurysm could be reliably measured by sonography. Additional 3D reconstructions could show flow parameters in the aneurysm more clearly, but imaging of the proximal and distal anchoring zone was only achieved insufficiently. After stentgraft implantation, possible complications like thrombus formation in the graft (4/50) and endoleaks (15/50) were clearly seen by power sonography. 9 anchoring leaks and 6 side-branch endoleaks were found. 3D power mode made localizing and imaging of aneurysm reperfusion easier. Detection of the origin of side-branch endoleaks was achieved only by DSA. Stent frame fractures (4/50) were difficult to see by ultrasound. CONCLUSIONS: Vascular ultrasound with power mode and 3D power mode makes the imaging of complications after endoaortic stentgraft implantation like endoluminal thrombus formation or endoleaks and the documentation of aneurysm reperfusion easier compared to CCDS. 3D reconstructions show the dimensions of the aneurysm but are not able to substitute CTA and DSA with measuring catheter for preinterventional planning.

Aged↗
PubMed2000

Aortic aneurysm size and graft behavior after endovascular stent-grafting: clinical experiences and observations over 3 years.

PURPOSE: To assess the long-term safety and efficacy of aortic endografts in terms of clinical outcome, continuing aneurysm exclusion, and changes of aneurysm size and graft configuration. METHODS: Between August 1994 and July 1997, 190 patients (176 men; mean age 68.7 years, range 40-87) with aortic and aortoiliac aneurysms were treated with endovascular stent-grafts (Stentor, Vanguard, and EGS) in a tertiary care municipal hospital setting. Follow-up involved clinic visits every 3 to 6 months with contrast-enhanced computed tomography (CT), color duplex, and plain abdominal radiographs at regular intervals; angiography was used selectively. All data were collected prospectively and entered into a computerized database. RESULTS: Implantation was possible in 188 (98.9%) patients. Early conversion to open surgical repair was required in 14 (7.4%) patients. Primary endoleaks were detected in 32 (16.8%) patients. Perioperative mortality was 0.53% (1/190). During follow-up, 17 (8.9%) additional patients were converted to open repair over a mean 20.9 months. Thirty-seven secondary procedures to treat endoleaks and pelvic outflow occlusions were performed in 30 (15.8%) patients. Changes in stent configuration suggestive of endograft disintegration were observed in 31 (29.8%) of 104 abdominal radiographs. Intraluminal layering of thrombus was seen on contrast-enhanced CT images in 20 patients. A significant trend (chi(2)4 = 12.34, p < 0.025) toward aneurysm enlargement was seen in patients with persistent endoleaks at a mean 18-month follow-up. CONCLUSIONS: Although endoleaks after aortic stent-graft placement tend to cause ongoing aneurysm growth, we have also observed aneurysm shrinkage despite ongoing endoleak. The presence or absence of an endoleak in itself may be a poor predictor of successful stent-graft therapy. Lifelong surveillance is needed to assure successful aneurysm exclusion and stability or shrinkage of the aneurysm sac. Technical improvements in stent materials and design are necessary to guarantee long-term stability and safety of the device.

Adult↗
PubMed2000

Guidelines for using human event-related potentials to study cognition: recording standards and publication criteria.

Event-related potentials (ERPs) recorded from the human scalp can provide important information about how the human brain normally processes information and about how this processing may go awry in neurological or psychiatric disorders. Scientists using or studying ERPs must strive to overcome the many technical problems that can occur in the recording and analysis of these potentials. The methods and the results of these ERP studies must be published in a way that allows other scientists to understand exactly what was done so that they can, if necessary, replicate the experiments. The data must then be analyzed and presented in a way that allows different studies to be compared readily. This paper presents guidelines for recording ERPs and criteria for publishing the results.

Cognition↗
PubMed2000

[Treatment of restenosis].

Carotid restenosis after endarterectomy is observed in up to 24.1% of patients with long-term follow up. Indication for reintervention in asymptomatic patients however should be reserved for greater than 80% stenosis. Treatment options include repeat surgical reconstruction as well as intraoperative or percutaneous balloon angioplasty +/- stenting. We compared our past experience with 66 operative reconstructions in 64 patients with a recent series of 60 patients who underwent intraoperative balloon-dilatation and stenting. After conventional surgery 2 patients (3.1%) suffered a permanent neurological deficit, one patient developed a TIA (1.5%). After intraoperative dilation and stenting 8 patients (13.3%) suffered a stroke; 2 patients died after surgery (one stroke, one myocardial infarction) (mortality 3.3%). When compared to conventional operative repair intraoperative carotid balloon angioplasty and stenting of restenosis is complicated by a substantial increase in morbidity and mortality and cannot be recommended as routine therapy.

Angiography, Digital Subtraction↗
PubMed2000

Mismatch negativity in children and adults, and effects of an attended task.

Attention has been shown to modulate the amplitude of the mismatch negativity (MMN) elicited by a small deviation in auditory stimuli in adults. The present study examined the effects of attention and deviant size on MMN amplitude in children. Children and adults were presented with sequences of tones containing standards (1000 Hz) and three deviants varying in degree of deviance from the standard (1050, 1200, and 1500 Hz). Tones were presented in three conditions: (1) while participants ignored them; (2) while participants listened to them and responded to all three deviants; and (3) while participants again ignored them. We found that the MMNs elicited by the hard deviant (1050 Hz) were larger when the children were actively discriminating the stimuli than when they were ignoring them. However, the MMNs elicited by the easy and medium deviants (1500 and 1200 Hz, respectively) in the children and by all three deviants in the adults were not affected by attention.

Adult↗
PubMed1999

Temporal integration of auditory stimulus deviance as reflected by the mismatch negativity.

We recorded event-related brain potentials (ERPs) to two different infrequent deviant tones presented successively within the repetitive sequence of a standard tone. A separate mismatch negativity (MMN) component was elicited by each of the two deviants when the interval separating their onsets was 300 ms. However, only a single MMN component was elicited when the temporal separation between the onsets of the two deviants was 150 ms. Previous studies obtained similar results using two temporally separated deviations carried by a single sound. Taken together, these results support the notion of a general temporal integration mechanism in the formation of auditory events with ca. 200 ms long window.

Acoustic Stimulation↗
PubMed1999

Changes in sensitivity to stimulus deviance in Alzheimer's disease: an ERP perspective.

The mismatch negativity (MMN) of the event-related brain potential (ERP) reflects the storage of information in sensory memory. MMNs were recorded from eight patients with Alzheimer's disease (AD) and eight controls to small (delta50 Hz), large (delta300 Hz), and a variety of highly deviant, environmental sounds. Both old controls and patients showed robust MMNs to all three classes of deviant events, and robust P3 compounds (indicative of active attention) to the environmental sounds. The data suggest that patients with mild AD have an intact sensory memory mechanism that responds similarly to that of controls to systematic increases in deviance. However, for both older controls and patients, only highly deviant acoustic events are likely to involuntary capture attention.

Acoustic Stimulation↗