Biomedical subjects

D K Brown

Publications and source records attributed to D K Brown.

At least 19 recordsLinked to original sources

PubMed1997

The effect of sound intensity on f1-sweep and f2-sweep distortion product otoacoustic emissions phase delay estimates in human adults.

Phase measurements of distortion product otoacoustic emissions (DPOAE) provide an estimate of round-trip travel times in the cochlea. This study examined differences in f1- and f2-sweep round-trip delays estimated from DPOAE phase responses in 20 normal-hearing adult human subjects as a function of f2 frequency and sound intensity. Eight different f2 frequencies ranging from 1.1-13 kHz were presented. For both the f1- and the f2-sweep stimulation conditions the f2/f1 ratios were between 1.1 and 1.3. Primary intensity levels for f2 were varied in 5-dB steps from 30-50 dB SPL (where f1 was 15 dB > f2). Delays in the f2-sweep condition were equal to or longer than travel times in the f1-sweep condition. Round-trip delays showed a significant intensity dependence in both the f1- and f2-sweep conditions (p < or = 0.01). In both conditions, the delay increased as stimulus intensity decreased. Delay estimates in the f2-sweep condition were more strongly intensity dependent than estimates in the f1-sweep condition at f2 frequencies above 1.6 kHz. The mean difference in f2- and f1-sweep delays at low intensities ranged from 15.9 periods at the 9.2 kHz f2 place, to 2.5 periods at the 1.6 kHz f2 place. The intensity dependence of round-trip delay estimates in both conditions may be attributed to intensity-dependent changes in the cochlear filter response time related to the sharpness of tuning of DPOAE responses. The steeper intensity dependence and longer delays observed in the f2-sweep condition may similarly be attributed to a greater proportion of the f2-sweep response being composed of the filter response time.

Acoustic Stimulation↗

PubMed1996

Comparison of distortion product otoacoustic emission (DPOAE) and auditory brain stem response (ABR) traveling wave delay measurements suggests frequency-specific synapse maturation.

OBJECTIVE: To determine whether the source of age-dependent latency changes for ABR wave I results from cochlear mechanics or the haircell-neuron synapse. DESIGN: Cochlear traveling wave delays were estimated on the basis of derived ABR response latencies and DPOAE phase delays. The difference in travel time between adjacent one octave-separated frequencies was calculated for four age groups: 30 to 33 wk old, 34 to 37 wk old, 38 to 42 wk old (term), and young adults. RESULTS: We found that there were essentially no travel time differences between newborns in the 34 to 37 and the 38 to 42 wk conceptional age (CA) groups as estimated from DPOAE phase delays. For the 30- to 33-wk-olds, DPOAE travel times were increased at all frequencies, likely due to mild (about 10 to 15 dB) conductive hearing losses. Differences in travel times between adjacent bands, however, were not different from the other neonatal groups. Estimates on basis of wave I latency showed delays for the high-frequency region, 6 to 11 kHz, that were still immature at term. CONCLUSIONS: A comparison of frequency-dependent travel times calculated for wave I and DPOAE data in comparable age groups suggests mature cochlear functioning at 35 wk CA and a delayed maturation for the haircell-auditory nerve synapses relative to the preneural components for the basal turn with center frequencies above 6 kHz.

Acoustic Stimulation↗

PubMed1995

A fatality associated with the deployment of an automobile airbag.

Airbags have become an increasingly accepted automobile safety feature that can reduce the morbidity and mortality associated with motor vehicle collisions. We present the following case report of an unusual fatality with multiple internal injuries from a minor mechanism motor vehicle collision. The cause of injuries was determined to be secondary to the deployment of a driver's side airbag without the concomitant use of a lap-shoulder belt.

Accidents, Traffic↗

PubMed1994

Prospective utility of cerebral proton magnetic resonance spectroscopy in monitoring HIV infection and its associated neurological impairment.

Neurological manifestations of HIV disease occur in most adults and children with AIDS. Many of those affected will inevitably suffer clinical neurological deficits involving mental function, movement, and sensation. Surprisingly, there are not as yet adequate monitoring systems to predict the onset and/or progression of HIV infection of the CNS. Neurological, neuropsychological, CSF, and magnetic resonance imaging (MRI) analyses cannot accurately detect mental deterioration during advancing HIV disease. Reports suggest that in vivo proton MR spectroscopy (1H MRS) of the brain could be a predictor of virus-induced neurological deterioration. H MRS can measure N-acetylaspartate (NAA), a metabolite present only in neurons. Decreased NAA reflects neuronal loss seen during HIV infection of brain. To uncover possible associations between NAA levels and HIV-induced neurological disease we performed serial 1H MRS brain tests in HIV-infected patients with or at risk for encephalopathy. Serial testing, for 1 year, of 10 patients showed that brain NAA levels decreased in all HIV-infected subjects. The most severe NAA reductions were associated with progressive neurological impairment. These findings suggest that NAA can be used as a noninvasive measure of neuronal loss in patients with HIV disease. Most important, the results suggest that 1H MRS could be used to monitor therapeutics directed against HIV infection within the CNS.

AIDS Dementia Complex↗

PubMed1994

Predicting pure tone thresholds in normal and hearing-impaired ears with distortion product emission and age.

Distortion product emission (DPE) growth functions, demographic data, and pure tone thresholds were recorded in 229 normal-hearing and hearing-impaired ears. Half of the data set (115 ears) was used by a discriminant analysis routine to classify DPE and demographic features into either a normal pure tone threshold (PTT) group or an impaired PTT group (PTT greater than 30 dB SPL) at six frequencies in the audiometric range. The six discriminant functions developed from this classification process were then used to predict pure tone threshold group membership in the remaining 114-ear data set. Frequency-specific prediction accuracy varied from 71% (correct classification of hearing impairment at 1025 Hz) to 92% (correct classification of normal hearing at 2050 Hz). Of the 45 DPE and demographic variables evaluated, the DPE amplitude associated with an f2 of moderate level (50 dB SPL) and a frequency corresponding to pure tone threshold was generally most predictive. DPE level was found to be weakly correlated with subject age and perhaps for this reason age was frequently included in discriminant functions. For our data, discriminant functions with one variable, two variables, or 5-10 variables showed no differences in predictive performance. This research suggests that DPE measures can reliably categorize pure tone thresholds as normal or impaired in large populations with varied cochlear hearing status.

Acoustic Stimulation↗

PubMed1993

Measuring human cochlear traveling wave delay using distortion product emission phase responses.

A method is presented here in which cochlear traveling wave delays are estimated through the measurement of distortion product emission phase (DPE) responses. This method assumes that the site of generation of DPEs is at the f2 place. Eighteen adult female and 18 adult male human ears, all with normal hearing, underwent DPE testing. For each ear, DPE phase responses were computed for eight values of f2 varying from 10 to 0.78 kHz. Linear DPE phase versus DPE frequency relationships were found. Estimates of traveling wave delay from the ear canal to the f2 place varied from about 1 ms for the 10-kHz place to 3.5 ms for the 0.78-kHz place. These estimates agree well with previous traveling wave delay estimates using electrocochleography. Test-retest comparisons of delay estimates were generally within 0.25 ms. In addition, within-subject interaural delay differences were smaller than between-subject interaural differences. Within-subject interaural delay differences were generally less than 0.5 ms. Male ears, when grouped together, had significantly longer delays (8%) to the 0.78-kHz place in comparison to female ears. The effect of DPE stimulus level on delay is presented for stimulus levels between 15 and 60 dB SPL. These data support the use of DPE phase responses as estimates of cochlear traveling wave delay. In comparison with electrophysiological and psychophysical techniques this method is purely cochlear-based and has the advantage of being rapid and noninvasive.

Auditory Perception↗

PubMed1993

Teacher use of descriptive analysis data to implement interventions to decrease students' problem behaviors.

We conducted two field studies using a behavioral consultation approach to reduce children's problem behaviors in public school settings. The first study consisted of a descriptive analysis in which the students and their teachers were observed during naturally occurring classroom activities. The results of the descriptive analysis provided hypotheses regarding the operant function of the students' problem behaviors. The hypotheses were tested in the second experiment directly through a modified experimental analysis and indirectly through an evaluation of the treatment effects. The interventions were designed to disrupt the inappropriate response-reinforcer relation by discontinuing contingent reinforcement (i.e., extinction), providing the reinforcer contingent on appropriate play behaviors, and teaching the students verbal skills functionally equivalent to the inappropriate response. The classroom teachers were trained to implement the interventions and conduct the experimental analyses during classroom activities in which the problem behaviors occurred most frequently. The interventions were effective in decreasing the students' problem behaviors while concurrently increasing their appropriate verbal skills.

Adolescent↗

PubMed1990

Solitary intrahepatic biliary cyst: diagnostic and therapeutic strategy.

This paper describes a newborn infant in whom an intrahepatic biliary cyst was successfully demonstrated by antenatal ultrasound. Postnatally, percutaneous cyst aspiration and computed tomography enhanced with intravenous cholangiographic contrast proved extremely helpful in the selection of surgical procedure. The lesion was completely removed at 12 weeks of age without complications.

Bile Duct Diseases↗

PubMed1989

Cross-sectional study of immunologic abnormalities in intravenous drug abusers on methadone maintenance in New York City.

One hundred and ninety-nine patients with a history of intravenous drug abuse, and enrolled on the St Luke's-Roosevelt Hospital Center Methadone Program, had baseline evaluations performed from September 1984 to April 1987. The study was designed to examine immunologic parameters associated with HIV seropositivity and those predictive of progression to AIDS-related complex (ARC) and AIDS. Sixty-four patients (32%) had antibodies to HIV by enzyme-linked immunosorbent assay (ELISA), with confirmation by Western blot and none of these patients had ARC or AIDS at the time of initial evaluation. The mean values for white blood-cell count, absolute lymphocyte count, proportion and absolute CD4, and CD4/CD8 ratio were decreased significantly in the HIV-seropositive group compared with the HIV-seronegative group. On the other hand, levels of circulating beta 2-microglobulin, SCD8, SIL-2R, and HIV p24 antigen were significantly elevated in the HIV-seropositive group compared with the HIV-seronegative group.

AIDS-Related Complex↗

PubMed1989

Comparison of treatments to teach number matching skills to adults with moderate mental retardation.

The effectiveness of the Dial-A-Phone (D-A-P) instructional package plus a least intrusive prompt hierarchy was compared to a least intrusive prompt hierarchy alone for teaching adults with moderate developmental disabilities to match digits of personal phone numbers with digits on a rotary dial telephone. Instructional programs were administered in the context of an alternating treatments design. The dependent variable was the percentage of digits matched independently per session (21 digits per session). Results suggest that although a least intrusive prompt hierarchy alone produced findings similar to the D-A-P plus prompts procedure for one subject, the D-A-P plus prompts package was the most effective in helping both subjects to match digits independently. Strategies for individualizing the D-A-P program were discussed.

Activities of Daily Living↗

PubMed1988

Behavioral momentum in the treatment of noncompliance.

Behavioral momentum refers to the tendency for behavior to persist following a change in environmental conditions. The greater the rate of reinforcement, the greater the behavioral momentum. The intervention for noncompliance consisted of issuing a sequence of commands with which the subject was very likely to comply (i.e., high-probability commands) immediately prior to issuing a low-probability command. In each of five experiments, the high-probability command sequence resulted in a "momentum" of compliant responding that persisted when a low-probability request was issued. Results showed the antecedent high-probability command sequence increased compliance and decreased compliance latency and task duration. "Momentum-like" effects were shown to be distinct from experimenter attention and to depend on the contiguity between the high-probability command sequence and the low-probability command.

Adult↗

PubMed1988

Squamous cell carcinoma of the anus: a twenty-five year retrospective.

Squamous cell carcinoma of the anus (SCCA), an aggressive and often fatal malignancy, has traditionally been treated with surgery. In recent years, however, nonoperative therapy has emerged as an alternative to operation. Twenty five years of experience with SCCA at this institution were reviewed to examine the presentation and outcome of a population treated primarily with surgery. Forty two patients, including 26 women and 16 men, had a mean age of 56 years. SCCA was usually heralded by a mass, bleeding, or pain and was associated with chronic perianal disease in 25.8%. Symptoms were present for an average of 11 months. Among the patients in this review, 92.3 per cent underwent radical surgery, while 11.9 per cent had radiation as their primary therapy following palliative surgery or local excisions for biopsy. Actuarial 5-year-survival for the entire group was 45.5 percent; all patients with nodal or disseminated disease at diagnosis have died. Patients with perianal lesions fared no better than those with anal tumors, probably due to the unusually large perianal tumors in this series. To diagnose SCCA at its earliest stage, a high index of suspicion must be maintained when dealing with anal and perianal lesions, especially if the abnormality is chronic. When compared with reported advances in combined therapy, it is likely that in most cases surgery alone no longer offers optimal treatment for SCCA.

Actuarial Analysis↗

PubMed1987

Peptic ulcer perforation associated with steroid use.

A ten-year (1974 to 1984) retrospective chart review was conducted to find all patients with peptic ulcer perforation associated with steroid treatment. During this period, 151 peptic ulcer perforations occurred, 25 (17%) associated with steroid use. Twenty patients had the diagnosis confirmed at operation, five at autopsy. The most common operative procedure was oversewing of the perforation with an omental patch (ten cases). Postoperative complications occurred in 16 patients and were multiple in 11. Underlying malignant neoplasms were the most common concurrent disease (11 patients), five patients having brain metastasis. Of 25 patients, 15 died--five preoperatively and ten postoperatively. Patients older than age 50 years had an overall mortality of 85%; those younger than age 50 years, 17%. A recurring pattern in 21 patients was perforation occurring after a major increase in steroid dose (pulse). Ulcer perforations associated with steroid use constitute a significant portion of all ulcer perforations, are lethal in most patients older than age 50 years, and are often associated with a steroid pulse before perforation.

Female↗

PubMed1986

Comparison of the spike precursor sequences of coronavirus IBV strains M41 and 6/82 with that of IBV Beaudette.

The nucleotide sequences of the spike precursor genes of infectious bronchitis virus strains M41 and 6/82 have been determined and compared with that of the Beaudette strain which we have previously sequenced. The two Massachusetts strains, M41 and Beaudette, were found to be remarkably similar, having only 3.7% of the amino acids different. The situation with 6/82, one of the new field isolates, is quite different and this strain had 13.8% of its amino acids different from Beaudette. The differences identified are discussed in terms of the structural features of the spike protein.

Amino Acid Sequence↗

PubMed1985