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Biomedical subjects

M Don

Publications and source records attributed to M Don.

At least 37 records · Page 2Linked to original sources
PubMed1994

Evaluating residual background noise in human auditory brain-stem responses.

The nature of the residual background noise in ABR averages was empirically examined in normal hearing objects. The residual noise in the average was estimated with use of the technique described by Elberling and Don [Scand. Audiol. 13, 187-197 (1984)]. Low-level click stimuli were presented in 2-dB steps spanning the range from 30 to 48 dB p-p.e. SPL. For each stimulus level, 10,000 sweeps were acquired and stored for analysis. Shortcomings of the use of artifact rejection and standard averaging are demonstrated. It is further demonstrated how application of the Bayesian estimation technique of Elberling and Wahlgreen [Scand. Audiol. 14, 89-96 (1985)] to form weighted averages can help minimize these shortcomings. Finally, the effects of smaller sweep block sizes on the Bayesian technique's ability to control the destructive effects of nonstationary noise are analyzed. Minimizing the destructive effects increases the value of statistical techniques used to detect objectively or to control the quality of ABR recordings. In all, these techniques in combination improve not only the accuracy of test interpretation but also the efficiency of clinical test time, which is becoming important for the control of medical costs.

Acoustic Stimulation↗
PubMed1993

Gender differences in cochlear response time: an explanation for gender amplitude differences in the unmasked auditory brain-stem response.

Derived narrow-band auditory brain-stem responses (ABRs) in young normal-hearing subjects revealed a significant gender difference in response time between frequency regions of the cochlea. Females showed shorter delays than males between derived bands. This differential has not been previously reported. As in many early studies, the unmasked amplitude of the wave V complex was significantly larger (30%) in females than males. However, differences in amplitudes of the narrow-band responses were too small to account for the differential in the unmasked response. It is hypothesized that the larger amplitude of the unmasked wave V complex in females occurs because of a faster response time across the cochlea leading to better neural synchrony and, therefore, larger amplitudes. Furthermore, results can be explained by assuming that the stiffness gradient in the cochlea is 13% larger in females than in males. If males and females have the same cochlear tonotopic mapping, the female cochlea should be 13% shorter. This prediction is highly consistent with recent anatomical studies of cochlear length and gender. The results of the present study indicated possibly important cochlear mechanisms that influence the main parameters of ABRs. An understanding of these cochlear mechanisms may improve the diagnostic capabilities of ABRs in patients with peripheral hearing loss.

Acoustic Stimulation↗
PubMed1992

Place-specific derived cochlear microphonics from human ears.

The high-pass noise masking technique was used to obtain derived frequency-specific cochlear microphonics (CM) from subtracted waveforms to rarefaction and condensation stimuli recorded with a tympanic membrane electrode. Two characteristics suggest that the response is place-specific CM: the derived response retains the same frequency as the stimulating toneburst and the response follows the stimulus polarity. For click stimulation, derived neural responses make the place-specific CM difficult to observe except in the 2-1 kHz derived band. In contrast, place-specific CM evoked by 0.5 and 1 kHz tonebursts can usually be detected in at least three derived bands. The amplitude of the response is largest in the derived band with center-frequency (CF) just above that of the toneburst. This discovery of a place-specific CM offers the possibility of assessing (outer) hair cell function in the apical part of the human cochlea.

Acoustic Stimulation↗
PubMed1991

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues.

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Acoustic Stimulation↗
PubMed1991

Pentamidine aerosol increases the number of alveolar macrophages in HIV-infected patients.

In order to determine the possible effect of aerosolized pentamidine on the cellular composition of the bronchoalveolar lavage fluid in HIV-infected patients, differential counts of 22 consecutive patients who had been rebronchoscopied after 3-19 months were reviewed. Eleven patients were started on pentamidine prophylaxis subsequent to their first presentation. Eleven patients had never taken pentamidine or had discontinued the prophylactic regimen. Compared to first bronchoscopy, the bronchoalveolar lavage (BAL) from patients on regular prophylaxis revealed a significant increase in absolute alveolar macrophage (AM) counts at second presentation (20.8 +/- 11.2 to 50.3 +/- 39.4 x 10(5) cells/100 ml BAL; P less than 0.01). The AM counts of those without pentamidine remained essentially unchanged. Lymphocytes, including CD4 and CD8 subtypes, and neutrophils did not change over time in either group. The results of this retrospective analysis suggest that, in addition to its antimicrobial action, pentamidine may modulate local lung defence mechanisms, particularly by increasing the absolute number of AM.

Administration, Inhalation↗
PubMed1989

Effects of click rate and electrode orientation on threshold of the auditory brainstem response.

This study evaluated the effects of stimulus presentation rate and electrode orientation on ABR threshold. Six normal-hearing adults served as subjects. ABRs were recorded from three orthogonal electrode pairs in response to click stimuli at rates of 48 and 21/s. Psychophysical thresholds were determined for each of these stimuli, and ABRs were recorded with stimuli between 0 and 10 dB SL in 2-dB steps. A ratio of ABR signal strength to noise variance (Fsp) was the criterion used to define threshold. Specifically, an Fsp value of 2.25, equivalent to a 95% response confidence using 5 and 250 degrees of freedom, was the criterion used to determine response presence within a maximum of 10,000 sweeps per average. Results revealed that, for normal-hearing adult subjects, click rate up to 48/s does not influence the sensation level at which a detectable response can be found, and a nearly vertical electrode orientation is optimal for recording the response at low levels. The predicted difference between psychophysical and ABR thresholds with a vertical electrode orientation, using 10,000 sweeps per average, up to 48 clicks per second, and an Fsp criterion of 2.25 is 4.4 dB.

Auditory Threshold↗
PubMed1988

Chemical modification of the actin binding site of rabbit muscle aldolase by diethylpyrocarbonate.

To extend the available information on the significance of the interactions between glycolytic enzymes and the actin component of the cellular ultrastructure, investigations into the compositional characteristics of the actin binding site on one of the major glycolytic enzymes, aldolase, have been undertaken. As the electrostatic nature of the association has been previously reported indicative of a cationic region on the enzyme involved in the binding, these studies have investigated the possibility of the involvement of histidine residues in this binding region. By the use of the histidine specific reagent, diethylpyrocarbonate, we have been able to establish a difference in nature of an actin binding domain and the active site domain which does contain an essential histidine. The results have been discussed in relation to the significance of this finding with respect to the binding of aldolase to subcellular structure.

Actins↗
PubMed1987

Glycolysis--new concepts in an old pathway.

A survey of the existing data on the interactions of glycolytic enzymes with the cellular structure in mammalian tissues has substantiated the occurrence of an extensive degree of such associations in all tissues and during all stages of development. Furthermore, a considerable specificity was evident between the individual multiple forms of the enzymes in relation to these associations. In reviewing these data, a model has been developed which proposes that the glycolytic sequence is best described as consisting of a number of segments in vivo, each segment formed by a cluster of isozymes, many of which can interact with the actin containing filaments of the cytomatrix. The novel features of this segmentation and compartmentation have been described, and evidence has been provided that these phenomena collectively play a key role in meeting the different types of energy requirement in the cytoplasm of divergent cell types, with the wide selection of isozymes in this system offering the potential for increased flexibility and control in this important area of metabolism.

Animals↗
PubMed1987

Induced temporary threshold shift in guinea pigs.

The etiology of an incidentally discovered temporary threshold shift observed in an experimental animal (Harley guinea pig) is discussed with its potential implications for auditory research.

Animals↗
PubMed1987

Threshold characteristics of the human auditory brain stem response.

Auditory brain stem responses (ABRs) were recorded from ten normal-hearing subjects in response to 100-microseconds clicks from a TDH 49 earphone at a rate of 48 pps and at levels randomly varied in 2-dB steps between 34 and 52 dB p.e. SPL. At each level, 10 000 epochs were averaged with use of a weighted concept and a running estimate was made of the signal-to-noise ratio (SNR). This quantity was used to detect the presence of the ABR and the median threshold was found at 38 dB p.e. SPL. The mean averaged background noise level was 11.3 nVrms, and the "true" ABRrms amplitude function crossed this value at 35.5 dB p.e. SPL, which indicates the level where the SNR = 1. By extrapolation, it was found that the ABR amplitude became zero at 32 dB p.e. SPL. The perceptual thresholds of the click were estimated by means of a modified block up-down procedure, and the median value was found at 33 dB p.e. SPL. The slope of the amplitude function and the magnitude of the averaged background noise are the two factors responsible for the ABR threshold sensitivity, which thus depends on both physiological and technical parameters. Therefore, these have to be considered together with the method of detection when the ABR is used to indicate the hearing sensitivity.

Auditory Threshold↗
PubMed1987

Detection functions for the human auditory brainstem response.

Previously obtained data characterizing the auditory brainstem response near the threshold for detection in 10 normal-hearing subjects are used to evaluate the detection method applied. The basic detection formula is described in terms of rates of true positive and false positive ABR detection and in combination with the normative ABR values used to calculate the ABR detection functions as well as the corresponding receiver operating characteristics (ROC curves). The observed distribution of the ABR-threshold levels is similar to that derived from the detection function, and therefore verifies the present results which are based partly on theoretical considerations.

Auditory Pathways↗
PubMed1987

The influence of deoxyribonuclease I and cytochalasin D on the release of glycolytic enzymes from digitonized cells.

In permeabilized cells, deoxyribonuclease I has been demonstrated to cause a decrease in the extent of binding to cellular structure of all of the glycolytic enzymes other than phosphofructokinase, with this decrease being most marked for aldolase and glyceraldehydephosphate dehydrogenase. Cytochalasin D, in contrast, did not produce this type of effect. These results have been discussed in relation to the evidence for the existence of a complex of glycolytic enzymes which binds to elements of the cytoplasmic matrix, and the possible organization of this complex.

Animals↗
PubMed1986

Mechanisms of central conduction time prolongation in brain-stem auditory evoked potentials.

The wave I-wave V delay in the auditory brain-stem response is commonly used as a diagnostic tool in otoneurology. Normative values have been established for different populations and different types of stimuli. This I-V delay has been known for some time as "central conduction time" or "central transmission time." This implies that the measure reflects in normal and in pathologic cases delays due to nerve conduction, synaptic transmission, and neural integration and is not caused by cochlear processes. By virtue of the traveling wave delay in the cochlea, amounting to some 4 ms from the base to the "500-Hz place," it is conceivable that this delay contributes to the I-V delay. From a series of 69 pontine angle tumors in which the auditory brain-stem response was recorded, we selected cases with an apparent peripheral origin of a prolonged I-V delay by comparing the whole-click response to responses derived from high-pass noise masking. It seems that cases with an increased I-V delay in the whole-click response but (almost) normal I-V delays in the narrow-band response are indicative of small intracanalicular acoustic neuroma.

Brain Stem↗
PubMed1984

Objective detection of averaged auditory brainstem responses.

Detection of an auditory brainstem response, ABR, usually relies on visual evaluation of two or more data acquisition runs of a fixed number of sweeps to determine if there is sufficient replication of the averaged waveforms to indicate a response. Visual interpretation can be difficult when the signal-to-noise ratio is poor because of either a small response or high levels of physiological background noise. Moreover, variations in the background noise from run to run can result in poor or spurious replications of component peaks and troughs in the waveform. A previous study (Elberling & Don, 1984) described a statistical approach for objective evaluation of the quality of an ABR recording. The method uses variance analysis in calculating the ratio of the magnitude of the ABR to the estimated averaged background noise. This study further applies this method to obtain a quantitative definition of the ABR threshold, to demonstrate its application in automatic threshold detection, and to estimate the number of sweeps required to reach detection criterion. Application of this method is valuable in reducing the variability of test interpretation and in maximizing the efficiency of recording ABRs by avoiding the averaging of excessive or insufficient numbers of sweeps. These improvements enhance the cost-benefit of ABR testing to the patient.

Adult↗
PubMed1984

Quality estimation of averaged auditory brainstem responses.

In its clinical use, the auditory brainstem responses, ABR, are recovered from the background noise by averaging a number of post-stimulus time epochs, sweeps. Normally, the test protocol prescribes a fixed number of sweeps to be employed and recording of replications is frequently recommended, too. Since both the ABR and the background noise differ in magnitude among patients and test sessions, such a test protocol can never ensure a given minimum "quality" or signal-to-noise ratio, SNR, of the averaged ABR. In an attempt to solve this problem, a method is proposed to evaluate, in statistical terms, the "quality" or SNR of the averaged recording. This is done by calculating the ratio between the estimated magnitude of the ABR and that of the averaged background noise. The method can be employed "on-line" in an adaptive strategy to estimate the number of sweeps necessary to obtain a given minimum "quality" of the averaged ABR. It can be used in suprathreshold recordings as well as in automatic "threshold" detection and it is a practical tool to analyze and improve the cost-benefit of the ABR test.

Audiometry↗