Search PubMed⌕ Search

Biomedical subjects

D O Kim

Publications and source records attributed to D O Kim.

At least 37 records · Page 2Linked to original sources
PubMed1996

Marginal shell of the anteroventral cochlear nucleus: acoustically weakly-driven and not-driven units in the unanesthetized decerebrate cat.

The ventral cochlear nucleus (VCN) of the cat is encapsulated by a marginal shell which is anatomically distinct from the central core of the VCN. Physiologically, little is known about the marginal shell. We report here a new finding that the marginal shell of the anteroventral cochlear nucleus (AVCN) in the unanesthetized decerebrate cat contains neural units which were weakly driven or not driven acoustically. The locations of the single units were histologically determined. Our observations also included other neural units of the marginal shell which were strongly driven acoustically; the latter results will be reported separately. The present physiological findings, together with previous anatomical findings of vestibular and somatosensory inputs to the AVCN marginal shell, suggest that some neurons of the AVCN marginal shell receive non-auditory sensory inputs besides weak auditory inputs and that these may play a role in multi-sensory processing.

Acoustic Stimulation↗
PubMed1995

Small neurons in the vestibular nerve root project to the marginal shell of the anteroventral cochlear nucleus in the cat.

We injected biotinylated dextran amine (BDA) into marginal shell regions of the anteroventral cochlear nucleus (AVCN) of the cat. These injections led to retrograde labeling of cells including small cells (median some area = 111 micron2, equivalent diameter = 11.9 microns) in the vestibular nerve root (VNR), just ventral to an anterior part of the AVCN. This is an unexpected new finding. The cells were scattered among BDA-labeled fibers and were oriented parallel to the course of the VNR fibers. We suggest that the small neurons of the VNR might serve as second-order vestibular neurons conveying information from vestibular end organs to the cochlear nucleus (CN) and/or act as interneurons between the olivocochlear fibers in the VNR and the CN.

Animals↗
PubMed1995

Role of echocardiography in the diagnosis of occult penetrating cardiac injury.

OBJECTIVE: To determine the usefulness of early echocardiography in stable patients with penetrating wounds in proximity to the heart. DESIGN: Retrospective chart review over a 1-year period. SETTING: Urban level I trauma center. PATIENTS: 121 clinically stable patients with penetrating wounds in proximity to the heart underwent immediate echocardiography (ECHO). Those with evidence of pericardial effusion then underwent subxiphoid pericardial window (SPW), followed by a median sternotomy if blood was found. RESULTS: Thirty patients had an ECHO that was positive and underwent immediate SPW. One patient with an initially negative ECHO deteriorated 5 hours after admission; a repeat ECHO was positive, and he also underwent SPW. In 16 of the 31 SPW performed, blood in the pericardial sac was confirmed. Of these 16, four had pericardial blood that cleared with irrigation and required no further intervention. The remaining 12 patients underwent exploration: 3 had injury to the pericardium only, 4 had injury to the right atrium, 3 had injury to the right ventricle, and 2 had injury to the left ventricle. All nine myocardial injuries required operative repair; all survived. CONCLUSIONS: Using the protocol of early ECHO and selective pericardial window, no clinically significant injuries were missed. In all, 12 penetrating cardiac injuries were identified and repaired successfully. We have found early and aggressive work-up, as outlined herein, to be helpful in the successful treatment of occult cardiac injuries.

Adolescent↗
PubMed1995

Spontaneous and sound-evoked discharge characteristics of complex-spiking neurons in the dorsal cochlear nucleus of the unanesthetized decerebrate cat.

1. We examined the spontaneous and sound-evoked discharge characteristics of 20 complex-spiking units recorded in the dorsal cochlear nucleus (DCN) of 15 unanesthetized, decerebrate cats. 2. The extracellularly recorded complex spikes consisted of bursts of two to five action potentials whose size gradually decreased during the burst. Complex spikes were observed both in the spontaneous and sound-evoked activity of the units in our sample. 3. The spontaneous rates (SRs) of DCN complex-spiking units ranged from 0 to 30 spikes/s. Spontaneous activity consisted of complex and simple (i.e., the common single neuronal action potential) spikes. Comparison of the SR distributions of the DCN complex-spiking units with that of a total sample of 194 DCN units (from 9 cats) suggests that the complex-spiking units tended to be in the lower half of the DCN SR distribution. 4. Sound-evoked discharges could consist of both complex and simple spikes. On the basis of their sound-driven responses, we divided the DCN complex-spiking units into two groups. The majority (15 of 20, 75%) were weakly driven by pure tones and inhibited by broadband noise. They tended to have broad response areas. Their response latencies to pure tone and noise stimuli were relatively long (10-20 ms). The recording depths of these units tended to be superficial (i.e., 10 of 15 units were located within 400 microns of the dorsal surface of the DCN). A minority (5 of 20, 25%) of the complex-spiking units were strongly driven by pure tone and broadband noise stimuli. These units had more clearly defined excitatory regions of response areas than the weakly driven units. Their response latencies to pure tone and noise stimuli were short (< 10 ms). The recording depths of these units tended to be deeper (i.e., 4 of 5 units were located at 400-700 microns) than those of the weakly driven units. 5. Intracellular recording and labeling studies of in vitro DCN slice preparations have correlated complex spikes with the superficially located cartwheel cells. Given the complex spikes of the units, many of which were located superficially, we suggest that our sample, particularly the weakly driven group of neurons, corresponds to the cartwheel cells. 6. Cartwheel cells are putative inhibitory interneurons whose axons primarily contact on the main projection neurons of DCN, the fusiform cells. The present finding of sound-evoked discharges by the superficially located complex-spiking units suggests that cartwheel cells should play a role in modifying the sound-evoked responses of the fusiform cells.

Acoustic Stimulation↗
PubMed1995

Aspiration of free blood from the peritoneal cavity does not mandate immediate laparotomy.

The objective was to establish the relationship between the aspiration of free blood (+ASP) versus diagnostic peritoneal lavage (DPL), abdominal injury severity, hemodynamic instability, and the need for immediate operative intervention. We prospectively compared the significance of +ASP to +DPL in our level I trauma center. Consecutive patients received sequential needle tap, catheter aspiration (ASP), and DPL. If gross blood was withdrawn during the tap or ASP, it was returned to the peritoneal cavity before completing the DPL. The DPL was considered positive if there were > 100,000 RBCs for blunt injuries or anterior abdominal stab wounds, or > 10,000 RBCs for other penetrating injuries. During a 12-month period, 566 patients fulfilled the study criteria; they were 50 per cent blunt and 50 per cent penetrating trauma. There were 70 patients with both +ASP/+DPL, 30 with -ASP/+DPL and 4 with +ASP but -DPL. Exploratory laparotomy was performed on these 104 patients (18.4%), 22 of which were considered nontherapeutic. The ATI was statistically higher in the +ASP patients (14.9 +/- 12.9 versus 8.5 +/- 8.2, P < 0.05) but was not clinically different. Overall injury severity and hemodynamic stability were not different in the two groups. The sensitivity of DPL at detecting intra-abdominal injury was higher than the ASP group (98% versus 72%), but the specificities were equal (98%). Because +ASP patients are not more critically injured or unstable than +DPL patients, and because DPL is more accurate in detecting the need for operative intervention, aspiration should be abandoned as part of the DPL procedure in patients with abdominal trauma.

Abdominal Injuries↗
PubMed1995

Prevention of postintubation laryngotracheal stenosis.

Laryngotracheal complications after translaryngeal intubation and specifically tracheotomy are a common problem. Surgical correction of PITS is not always successful. Pathogenetic mechanisms of PITS are direct pressure necrosis by overinflated endotracheal tube and cuff material, duration of intubation, macro- and microtrauma during intubation, the specific technique of endotracheal intubation, severity of respiratory failure, infection and poor tissue perfusion due to hemodynamic instability. Following preventive guidelines are proposed: the use of high volume low pressure cuffs, cuff pressure monitoring, ventilatory support with lower airway pressures, prevention of macrotrauma during intubation and microtrauma during maintenance, adapted policy of choice between translaryngeal and tracheotomy techniques, anti-infectious strategy and swift hemodynamic stabilization.

Hemodynamics↗
PubMed1994

A computational model with ionic conductances for the fusiform cell of the dorsal cochlear nucleus.

A computational model of a fusiform cell of the dorsal cochlear nucleus was developed. The results of model simulations are compared with the results of in vitro experimental observations obtained by other investigators. The structure of the present model is similar to that of Hodgkin-Huxley [J. Physiol. 117, 500-544 (1952)]. The model incorporates five nonlinear voltage-dependent conductances (three potassium and two sodium types) and their associated equilibrium-potential batteries, a leakage conductance, the membrane capacitance, and a current source. Model responses were obtained under both current- and voltage-clamp conditions. When a hyper- and depolarizing current sequence was applied [Manis, J. Neurosci. 10, 2338-2351 (1990)], the cell model was able to reproduce builduplike and pauserlike discharge patterns closely resembling Manis' observations. A transient "A"-type potassium conductance in the model played a major role in generating this phenomenon. The model predicts that blocking the "A" conductance should convert a builduplike or pauserlike pattern into a sustained regular pattern. A persistent sodium conductance in the model played the main role in reproducing: Spontaneous regular discharge; a discharge after a long latency under a long small (+0.025 nA) current; and nonlinear voltage-current characteristics with positive currents. Usefulness of the model can be seen as follows: (1) Several sets of experimental observations can be integrated into a common framework; (2) possible roles of different ionic conductances postulated to be present in the cell can be inferred by observing the model behavior with the conductances intact or blocked; and (3) time courses of ionic currents and conductance values obtained from the model under current- and voltage-clamp conditions can serve as predictions to be tested in future experimental studies.

Cochlea↗
PubMed1993

Diversion colitis in patients scheduled for colostomy closure.

Despite recent work, diversion colitis remains poorly defined. Thirty-four patients, scheduled for colostomy closure, were prospectively evaluated with flexible sigmoidoscopy for diversion colitis. Biopsies and cultures were obtained if colitis was identified at endoscopy. All biopsy materials and cultures were consistent with inflammation only. The vast majority of patients were in good general health, and their colostomies were constructed as the result of trauma. Eight patients (24 percent) had normal-appearing colons at an average of 16.6 weeks following diversion. Twenty-six patients (76 percent) demonstrated mild to severe colitis at an average of 29.9 weeks following diversion. Three complications occurred in 22 patients after colostomy closure: two wound infections in patients with colitis and one in a patient with a normal colon. We conclude that diversion colitis in an otherwise individual constitutes no increased risk of infection following colostomy closure.

Adult↗
PubMed1993

Distortion-product and click-evoked otoacoustic emissions of preterm and full-term infants.

Full-term and preterm infants were evaluated with click-evoked and distortion-product otoacoustic emissions (CEOEs and DPOEs). The CEOEs and DPOEs recorded from each individual ear were analyzed by calculating the root-mean-square levels within half-octave bands. The fail criterion of the OE tests was that the half-octave RMS DPOE or CEOE levels of an ear under test were below the 10th percentile of full-term newborns in two or more bands. The DPOE data were collected from 118 ears of 61 premature babies; 80 (68%) ears passed the DPOE test, 30 (25%) ears without middle ear effusions failed the test, and 8 (7%) ears with effusions also failed. The CEOE data were collected from 128 ears of 65 premature babies; 102 (80%) ears passed the CEOE test, 18 (14%) ears without middle ear effusions failed the test, and 8 (6%) ears with effusions also failed. In 23 of 80 ears (29%) that passed the DPOE test and in 23 of 102 ears (23%) that passed the CEOE test, RMS OE levels of preterm infants were above the 90th percentile of full-term newborns. The analyses of the combined DPOE and CEOE data obtained from a group of 25 ears of full-term newborns and from a group of 72 ears of preterm babies showed statistically significant correlations between the DPOE and CEOE root-mean-square levels in each of the half-octave bands in the 1.4 to 4 kHz region. For 42 preterm infants tested with auditory brain stem response (ABR), specificity was 86% for CEOE and 74% for DPOE. All infants who failed the ABR also failed OE tests. To the best of our knowledge, this study is the first using combined DPOEs, CEOEs, and ABRs for preterm babies. It showed the feasibility of DPOEs and CEOEs for this population.

Acoustic Impedance Tests↗
PubMed1993

Discharge suppression in the silent interval preceding the tone burst in pause-build units of the dorsal cochlear nucleus of the unanesthetized decerebrate cat.

A recent intracellular study of dorsal cochlear nucleus (DCN) neurons in vitro by Manis [P. B. Manis, J. Neurosci. 10, 2338-2351 (1990)] suggests that the expression of the pause-build discharge pattern is in large part dependent on hyperpolarization of their membrane potentials in a period just preceding a depolarizing stimulus ("hyperpolarization conditioning" hypothesis). Our examination of the activity of a sample of pause-build units (n = 72) revealed suppression of discharge activity during a time window of the silent interstimulus interval (SII) just preceding the tone burst relative to the spontaneous rate in 74% of all units. The discharge suppression of a subset of DCN pause-build units in the SII satisfies a requirement of the "hyperpolarization conditioning" hypothesis, and thus supports the hypothesis.

Acoustic Stimulation↗
PubMed1993

Otoacoustic emissions in full-term newborns at risk for hearing loss.

Distortion product otoacoustic emissions (DPOEs) and click-evoked otoacoustic emissions (CEOEs) characteristics of the normal newborn population have been previously reported in the literature. There is little information about DPOE evaluations in the newborn population at risk for hearing loss. The authors now report the DPOE and/or CEOE data from six full-term subjects at risk for hearing loss or with highly suspected hearing loss. These subjects were less than 1 year of age and at risk for hearing loss secondary to a history of hereditary hearing loss, meningitis, hyperbilirubinemia, and ototoxic drug exposure. Audiometric evaluation included auditory brainstem responses (ABR), behavioral observation audiometry, and tympanometry. The CEOEs and DPOEs were found to be decreased or absent in the subjects with suspected hearing loss secondary to cochlear pathology; they were found to be normal in a subject with a suspected central hearing loss. This study's data suggest that otoacoustic emissions when combined with ABR can provide a frequency-specific evaluation of cochlear function and help determine the anatomic site of a pathologic lesion.

Acoustic Impedance Tests↗
PubMed1992

Amplitude-modulated tone encoding behavior of cochlear nucleus neurons: modeling study.

A recent study of amplitude-modulated (AM) tone encoding behavior of dorsal and posteroventral cochlear nucleus (DCN and PVCN) neurons by Kim et al. [Hear. Res. 45, 95-113, 1990] observed that certain neurons (e.g., pause/build type-III neurons and chop-S neurons) tended to exhibit band-pass modulation transfer functions (MTFs) and intrinsic oscillations (IOs) whereas certain other neurons (e.g., chop-T neurons) tended to exhibit low-pass MTFs and no IOs. The goal of the present study was to develop models of these response characteristics in an attempt to understand the underlying neuronal mechanisms. We hypothesized that chopper neurons corresponded to stellate cells and pause/build neurons corresponded to fusiform cells. We also hypothesized that, with right input combination, appropriate models of a single stellate and fusiform cell could account for band-pass and low-pass MTFs as well as the associated IOs. The neuron models developed by Arle and Kim [Biol. Cybern. 64, 273-283, 1991] for the stellate and fusiform cells were used in this study. The models are modified versions of MacGregor type neuron model incorporating cell-specific nonlinear voltage-dependent conductances. The AM tone excitation via the auditory nerve fibers was represented by a current at the soma of the neuron model, which consisted of dc, ac and a zero-mean Gaussian noise. The dc, ac and noise represent a high-frequency carrier beyond the neuron's phase-locking limit, an envelope, and randomness of the system, respectively. With systematic variation of dc, ac and noise amplitudes, we observed the following: the band-pass MTF behaviors of pause/build and chop-S neurons were reproduced by the fusiform cell model and the stellate cell model with a strong dc/noise ratio, respectively. The low-pass MTF behavior of a chop-T neuron was reproduced by the stellate cell model with a weak dc/noise ratio. It was observed that the stellate cell model was more susceptible to the noise, in the sense that an increase in noise tended to abolish the IO and change the MTF of the model from band-pass to low-pass more readily in the stellate cell model than in the fusiform cell model. Kim et al. (1990) observed a close correlation between the IO frequency and the best envelope frequency (BEF). In the models, a similar correlation was observed between the two measures for both the stellate and fusiform cell models.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

Distortion-product and click-evoked otoacoustic emissions of normally-hearing adults.

The purpose of this study was to compare distortion-product otoacoustic emissions (DPOEs) and click-evoked otoacoustic emissions (CEOEs) for normally-hearing human adults. The statistical analysis consisted of computing the DPOE and CEOE levels versus frequency corresponding to the 10th, 25th, 50th, 75th, and 90th percentiles among normal adult ears. The mean and standard deviations of the DPOEs and CEOEs were computed. A direct comparison of the DPOE and CEOE data obtained from the same ears showed that, in a 1-4 kHz frequency region, there was a statistically significant correlation between the levels of the two types of otoacoustic emissions. This finding supports the hypothesis that DPOEs and CEOEs arise from some common mechanisms of the cochlea such as active nonlinear biomechanical mechanisms of the outer hair cells.

Acoustic Stimulation↗
PubMed1992

Analysis of temporal discharge characteristics of dorsal cochlear nucleus neurons of unanesthetized decerebrate cats.

1. We examined the mean and standard deviation (SD) of interspike intervals (ISI) and the coefficient of variation (CV, the ratio of SD of ISI to mean ISI) of ISIs versus time to study discharge regularity of units in the dorsal cochlear nucleus (DCN) of decerebrate unanesthetized cats. The units were characterized by the use of both poststimulus time histograms (PSTH) and excitatory-inhibitory area (EI-area) schemes. We present results of a systematic examination of all of 87 DCN pause-build units recorded in this study. In addition, we present examples of chopper subtypes of the DCN. 2. A major finding of this study is that a majority of the pause-build units in the present sample exhibited regular discharges in response to short (50 ms) tone bursts at characteristic frequency (CF), as revealed by CVs less than 0.5. A predominant portion of pause-build units (80% of 44 units with sufficient number of spikes for CV analysis) exhibited mean CVs less than 0.5 in the 20- to 39.9-ms time window in response to 50-ms tone burst at CF at 60 dB SPL re 20 microPa; 39% of the 44 units exhibited highly regular discharges (mean CV less than 0.35). During the onset (2-14.9 ms) time window, 77% (of 53 units with sufficient number of spikes for CV analysis) of the units had mean CVs less than 0.5, and 55% were less than 0.35. 3. In our sample of 87 DCN pause-build units, 59% had spontaneous rates (SR) greater than 15 spikes/s. The pause-build units of the present sample were distributed across four different EI-area types: III (51%), I/III (25%), II (15%), or IV (9%). In the 20- to 39.9-ms time window, the pause-build units with mean CVs less than 0.35 were exclusively of types III and I/III. All of the above EI-area types were represented in the lowest CV group for the 2- to 14.9-ms window. 4. The mean ISIs of DCN pause-build units typically showed a decrease during the first 20-25 ms of the response to 50-ms CF tone bursts, and stable mean ISIs in the latter half, when off-discharges were absent. In the presence of off-discharges, the mean ISIs decreased further in the last 5-10 ms of the response.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Distortion-product and click-evoked otoacoustic emissions in healthy newborns.

Distortion-product otoacoustic emissions (DPOEs) are believed to provide frequency-specific information about cochlear function. The DPOEs have been reported in the adult population but have not been reported previously in the neonatal population. We recorded DPOEs from a group of healthy full-term newborn human subjects (35 ears) to establish the characteristics of these emissions in the newborn population. To our knowledge, this is the first study of DPOEs in newborns. The "DPOE audiograms" from the newborns tested revealed characteristics qualitatively similar to those seen in adults with normal hearing. This study demonstrates the feasibility of DPOE measurements among newborns and provides a normal baseline for this age group, thus fulfilling a necessary step toward the development of an objective, noninvasive frequency-specific test of cochlear function. Click-evoked otoacoustic emissions were also recorded from the newborn population and compared with click-evoked otoacoustic emissions from adults. The spectrum of the click-evoked emissions was variable and individualistic, similar to findings previously reported in adult subjects. The click-evoked otoacoustic emissions of the newborns had a higher overall level and contained stronger high-frequency (4.5 to 6 kHz) spectral components than those of the adults. We also found that the low-frequency components of the click stimulus spectrum were attenuated in the neonatal ears exhibiting a high-pass slope below about 2.5 kHz, whereas the stimulus spectrum was nearly flat in this frequency region in adult ears.

Acoustic Stimulation↗
PubMed1991

Neural modeling of intrinsic and spike-discharge properties of cochlear nucleus neurons.

The purpose of this study was to develop neurobiologically plausible models to account for the response properties of several types of cochlear nucleus neurons. Three cell types--the bushy cells, stellate cells, and fusiform cells--were selected because useful data from intracellular recordings were available for these cell types, and because these three cell types exhibit distinct contrasts in their neuronal signal coding strategies. Stellate cells have primarily linear current-voltage (I-V) characteristics, but both bushy and fusiform cells have highly non-linear I-V characteristics. In light of this, we hypothesize that some of these cells have non-linear voltage-dependent conductances which alter their response properties. We modeled the bushy cell membrane conductance as an exponentially increasing function of membrane voltage, that of the fusiform cell as an exponentially decreasing function of the voltage, and that of the stellate cell as being voltage-independent. We have combined the voltage-dependent non-linear conductances of the cell membrane with a simple R-C circuit type of neuron model. These models reproduced the salient features of the experimentally observed I-V characteristics of the cells. In addition, we found that the models reproduced the spike discharge behavior to intracellularly injected current steps. Moreover, a more detailed study of stellate cell 'chopper'-type response patterns yielded hypotheses regarding the nature of the current that must exist at the soma during a pure-tone stimulus in order for the cells to exhibit various chopper subtype patterns, such as chop-S, chop-T, and Oc. The chop-S pattern requires a steady average current level with a relatively small variability during the tone-burst stimulus. The chop-T pattern, in contrast, requires that the current become more irregular during the tone-burst stimulus. The Oc pattern arises, however, when the input is similar to the chop-T case but the intrinsic properties of the cell model have been changed to increase the accommodation of the threshold. The implications of these findings for circuitry in the cochlear nucleus are discussed. Our analysis of these models revealed that this approach can be used to simulate neuronal cell types where I-V characteristics are known but more detailed ion channel data are not known.

Animals↗
PubMed1991

Auditory nerve spatial encoding of high-frequency pure tones: population response profiles derived from d' measure associated with nearby places along the cochlea.

We examined a measure of discriminability in auditory nerve (AN) population responses that may underlie behavioral frequency discrimination of high-frequency pure tones in the cat. Population responses of high- (greater than = 15 spikes/s) and low- (less than 15 spikes/s) spontaneous rate (SR) AN fibers in unanesthetized decerebrate cats to 5 kHz pure tones were measured in the form of mean, mu, and standard deviation, sigma, of spike counts for 0.2 s tone bursts. The AN responses were analyzed in terms of a d'e(x, delta x) associated with adjoining cochlear places as defined in the manner of signal detection theory. We also examined sigma d'e(x, delta x), a spatial summation of the discriminability measure. The major findings are: (1) the d'e(x, delta x) function conveys information about 5 kHz pure tone frequency over a region of +/- 0.5 to 1.0 octave, or +/- 1.67 to 3.33 mm, around the characteristic place (CP), with the region being narrower at lower stimulus levels; (2) at 30 dB SPL, the integrated d'e(x, delta x) discriminability scores are similar for the apical and basal regions surrounding the CP whereas, at 70 dB SPL, the scores are higher for the apical region than for the basal region; and (3) at 50 and 70 dB SPL, the integrated d'e(x, delta x) discriminability scores of low-SR fibers were higher than those of high-SR fibers although, at 30 dB SPL, the latter were higher than the former. By using the cat cochlear frequency-place relationship and the inner hair cell (IHC) spacing, we interpret that the cat's frequency difference limen, delta f/f = 0.0088 at 4 kHz [Elliott et al., 1960, J. Acoust. Soc. Am. 32, 380-384], corresponds to a shift of cochlear excitation profile by 4.5 IHCs. From the present analysis of AN responses, we conclude that, for high-frequency pure tones, the d'e(x, delta x) code, an example of rate-place code, of frequency provides sufficient information to support the cat's behavioral frequency discrimination.

Acoustic Stimulation↗