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Biomedical subjects

J E Hirsch

Publications and source records attributed to J E Hirsch.

15 recordsLinked to original sources
PubMed2001

Dynamic Hubbard model.

The Hubbard on-site repulsion U between opposite spin electrons on the same atomic orbital is widely regarded to be the most important source of electronic correlation in solids. Here we extend the Hubbard model to account for the fact that the experimentally measured atomic U is different from the one obtained by calculation of the atomic Coulomb integral. The resulting model describes quasiparticles that become increasingly dressed as the number of electrons in the band increases. Superconductivity can result in this model through quasiparticle undressing. Various signatures of this physics in spectroscopies in the normal and superconducting states are discussed. A novel effect in the normal state is predicted to be electroluminescence at the sample-positive counterelectrode boundary.

Journal Article↗
PubMed1999

Hearing screening in the newborn intensive care nursery: comparison of methods.

Patients in the neonatal intensive care unit were tested by hearing screening tests including auditory brain stem response (ABR), transient and distortion-product otoacoustic emissions (TEOAEs and DPOAEs), and acoustic stapedius reflex (ASR), and by middle ear function tests including multifrequency tympanometry and pneumatic otoscopy. Pass rates on hearing tests were 75% to 89%. TEOAEs produced the lowest pass rate, and DPOAEs the highest. TEOAE, DPOAE, or ASR testing followed by ABR testing of initial failures produced pass rates of about 90%. The most efficient combination was DPOAEs followed by ABR. Pass rates tended to decrease with age. Of patients who failed 226-Hz and 678-Hz tympanometry, 30% to 67% passed hearing tests, suggesting a high false-positive rate for these immittance tests. The 3 ears that failed the 1000-Hz tympanogram failed all hearing tests. Many ears were abnormal by pneumatic otoscopy but passed hearing tests, suggesting that the usual ear examination criteria may not apply to infants.

Evoked Potentials, Auditory, Brain Stem↗
PubMed1998

Continuous adult development of multiple innervation in toadfish sonic muscle.

The sonic muscle of the oyster toadfish Opsanus tau produces unfused contractions at over 200 Hz for mating call production, requiring extreme muscle fiber synchronization. This multiply innervated muscle is sexually dimorphic and grows for life by fiber proliferation and hypertrophy. Previous descriptions of its multiple innervation did not consider fish size or sex. We examined neuromuscular junction (NMJ) development in adult fish of both sexes between 123 and 343 mm in total length (24.7790 g in mass). The NMJ was a tubelike trough that varied in length from 8 to 178 microm. Troughs were usually straight, although some consisted of consecutive ovals and some were branched. Median length of NMJs increased linearly with fish length (r2=.40; p=.002) from 58 to 75 microm. Modal lengths were mostly between 50 and 60 microm and did not increase ontogenetically, indicating that the median increase was caused by a greater number of large junctions in older fish. Median interval between NMJs (measured from the beginning of one junction to the next) ranged from 92 to 116 microm and did not vary with fish size (r2=.06; p=.285). Considering muscle fiber elongation, the data indicate an increase from 60 to 140 NMJs per fiber during fish growth. There were no sexual differences in NMJ length or spacing. In view of the slow conduction velocity of sonic muscle fibers, the addition of new NMJs and the relatively constant distance between them supports rapid and synchronized contraction necessary for sound production in both sexes.

Acetylcholinesterase↗
PubMed1993

The effect of middle ear pressure on transient evoked otoacoustic emissions.

To determine the effect of middle ear pressure on transient evoked otoacoustic emissions (TEOAEs), emissions were recorded in ears with tympanometric peak pressures < or = -100 daPa and audiometric thresholds < or = 30 dB HL at 500 through 2000 Hz. TEOAEs were alternately recorded at ambient pressure and at the tympanometric peak pressure. As demonstrated for the 14 ears tested, equalization of the middle ear pressure increased TEOAE amplitude. Reproducibility was similarly improved in 12 of 14 ears. Unequalized middle ear pressure attenuated low frequency emissions more than high frequency emissions. These amplitude and spectrum differences were consistent with previously reported observations of the effects of ear canal pressure on otoacoustic emissions. Results suggest that unequalized middle ear pressure may increase the occurrence of false positive failures, if otoacoustic emission testing is used for hearing screenings without consideration of middle ear pressure.

Acoustic Impedance Tests↗
PubMed1992

A comparison of acoustic reflex and auditory brain stem response screening of high-risk infants.

This investigation was undertaken to explore the feasibility of screening for hearing impairment in an intensive care nursery population with a combined acoustic stapedius reflex-ABR approach. Acoustic reflex threshold measurements (AR) were made on intensive care nursery patients in an existing ABR screening program. Pass-fail results were determined for the two methods, separately and in combination. AR screening identified all 10 ears that failed the ABR screen. The cost savings of screening with a combined AR-ABR approach was determined for various pass-fail criteria. The results suggest that the AR-ABR approach can produce a significant cost savings without compromising the sensitivity and specificity of the screening program.

Acoustic Impedance Tests↗
PubMed1980

Effects of stimulus rise-fall time and equivalent duration on middle components of AER.

Tone bursts of 500, 1 000, or 3 000 Hz with rise/fall times of 3, 5, and 10 msec were combined with either a 'no plateau' duration or 'equivalent durations' of 10 or 30 msec. Electroencephalic activity (102.4 msec post-stimulus) from normal-hearing adults was recorded between the vertex and each earlobe. AER latencies and amplitudes decreased as frequency increased but effects of increasing rise/fall time and duration were similar at all frequencies. An increase in stimulus rise/fall time or equivalent duration results in increases of about 1-3 msec in latencies of all middle component peaks. Increasing either rise/fall time or equivalent duration produces a considerable reduction in middle component amplitude at all intensity levels. Any combination of rise/fall time and plateau duration that gives an equivalent duration of less than 10 msec. and results in narrow spectra stimuli, appears optimal for clinical EEA with middle components.

Acoustic Stimulation↗
PubMed1979

Toward objective analysis for electroencephalic audiometry.

Middle-component AERs (8-90 msec) to tone-pips from 10 normal-hearing adults were subjected to three objective methods of response identification. Threshold was then determined for each subject according to four different rules. The criterion score, which considers conjointly latency and amplitude values across the middle-component peaks, was developed as a single-value measure for response-identification and subsequent threshold-determination procedures. One of the response-identification methods was applied to 10 hearing-impaired subjects; the results of the threshold-determination procedures were encouraging. Further directions toward improving objective response analysis are discussed.

Audiometry↗
PubMed1979

Ventilation response and drive during hypoxia in adult patients with asthma.

We studied ventilation and inspiratory muscle activity during progressive isocapnic hypoxia in adult asthmatic patients to determine whether the decreased hypoxic ventilatory response previously identified is due to the mechanical abnormalities of the respiratory system or to low respiratory center output. The mouth pressure produced by inspiratory muscle activity, a reflection of respiratory center output, was measured at 100 msec of inspiration against an occluded airway at functional residual capacity. At end-tidal oxygen tension (PETO2) of 80 mm Hg, inspiratory muscle activity was greater in asthmatic patients than in normal subjects for the same level of ventilation, but at PETO2 of 40 mm Hg, both inspiratory muscle activity and ventilation were lower in asthmatic patients. Consequently, the changes in inspiratory muscle activity and ventilation per mm Hg change in PETO2 were lower in the asthmatic patients. To generate the same ventilation during progressive hypoxia, more inspiratory muscle activity was needed by asthmatic patients. We concluded that the decreased hypoxic ventilation in asthmatic patients resulted from both decreased respiratory center output and from mechanical abnormalities of the respiratory system.

Adolescent↗
PubMed1978

The role of hyperventilation in exercise-induced bronchoconstriction.

Significant bronchoconstriction, comparable in severity to that observed after moderate treadmill exercise, was induced in asthmatic children by voluntary isocapnic hyperventilation of 3-min and 10-min duration. In both hyperventilation and exercise, nasal breathing inhibited the bronchoconstrictive responses, whereas mouth breathing potentiated the bronchoconstrictive response. In the asthmatic children, 10 min of voluntary isocapnic hyperventilation did not represent a greater bronchoconstrictive stimulus than did 10 min of exercise or 3 min of isocapnic hyperventilation. This study also showed that in normal children there was no measurable airway response after either voluntary isocapnic hyperventilation or moderate exercise. Finally, this study indicates that it is the stimulation of upper airway receptors by relatively cold and dry air, rather than hyperventilation per se, that provokes exercise-induced bronchoconstriction.

Adolescent↗
PubMedDate not supplied

Early- and middle-aer components to clicks as response indices for neonatal hearing screening.

Early- and middle-component-averaged electroencephalic responses (AER) to monotic clicks at 60, 40 and 20 dB normal hearing level were elicited from 18 carefully selected normal neonates. Grand-composite AERs of the responses from all 18 babies showed stimulus-related configurations at all three stimulus levels. AERs for individual babies were more frequently identified as stimulus-related when poststimulus activity beyond 10 ms was included in response-identification procedures than when only the first 10 ms was observed.

Audiometry↗