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Biomedical subjects

J C Sun

Publications and source records attributed to J C Sun.

At least 19 recordsLinked to original sources
PubMed2001

Origin of vestibular dysfunction in Usher syndrome type 1B.

It is still debated to what extent the vestibular deficits in Usher patients are due to either central vestibulocerebellar or peripheral vestibular problems. Here, we determined the origin of the vestibular symptoms in Usher 1B patients by subjecting them to compensatory eye movement tests and by investigating the shaker-1 mouse model, which is known to have the same mutation in the myosin-VIIa gene as Usher 1B patients. We show that myosin-VIIa is not expressed in the human or mouse cerebellum and that the vestibulocerebellum of both Usher 1B patients and shaker-1 mice is functionally intact in that the gain and phase values of their optokinetic reflex are normal. In addition, Usher 1B patients and shaker-1 mice do not show an angular vestibuloocular reflex even though eye movement responses evoked by electrical stimulation of the vestibular nerve appear intact. Finally, we show histological abnormalities in the vestibular hair cells of shaker-1 mice at the ultrastructural level, while the distribution of the primary vestibular afferents and the vestibular brainstem circuitries are unaffected. We conclude that the vestibular dysfunction of Usher 1B patients and shaker-1 mice is peripheral in origin.

Animals↗
PubMed2001

Hereditary familial vestibular degenerative diseases.

Identification of genes involved in hereditary vestibular disease is growing at a remarkable pace. Mutant mouse technology can be an important tool for understanding the biological mechanism of human vestibular diseases.

Animals↗
PubMed2001

Recognition and management of atlanto-occipital dislocation: improving survival from an often fatal condition.

OBJECTIVE: To provide an overview of atlanto-occipital dislocation and associated occipital condyle fracturcs so as to alert physicians to this rare injury and potentially improve patient outcome. The pertinent anatomy, mechanism of injury, clinical and radiologic evaluation and the management of these rare injuries are discussed in an attempt to alert physicians to this type of injury and to improve outcome. DATA SOURCES: The data were obtained from a MEDLINE search of the English literature from 1966 to 1999 and the experience of 4 spine surgeons at a quaternary care acute spinal cord injury unit. STUDY SELECTION: Detailed anatomic and epidemiologically sound radiology studies were identified and analyzed. Only small retrospective studies or case series were available in the literature. DATA EXTRACTION: Valid anatomic, biomechanical and radiologic evaluation was extracted from studies. Clinical data came from limited studies and expert opinion. DATA SYNTHESIS: Early diagnosis is essential and is facilitated by a detailed clinical examination and strict adherence to an imaging algorithm that includes CT and MRI scanning. When the dislocation is identified, timely gentle reduction and prompt stabilization throuigh nonoperative or operative means is found to optimize patient outcome. CONCLUSIONS: Atlanto-occipital dislocation should be suspected in any patient involved in a high speed motor vehicle or pedestrian collision. Once suspected, proper imaging and appropriate management of these once fatal injuries can improve survival and neurologic outcome.

Atlanto-Occipital Joint↗
PubMed2000

Hemorrhagic moyamoya disease during pregnancy.

BACKGROUND: Intracranial hemorrhage in pregnant patients with Moyamoya disease is rare. We review the case of one such patient who presented with pre-eclampsia and a catastrophic intracerebral hemorrhage in order to highlight the associated management difficulties. METHODS: A case of a pregnant (31 weeks) female brought to the emergency department with hypertension and a progressive decrease in her level of consciousness is presented. She rapidly developed a dilated right pupil and left extensor posturing. A CT scan of her head showed a large putamenal intracerebral hemorrhage. She was intubated, ventilated and given intravenous mannitol and magnesium sulfate. She underwent a simultaneous craniotomy and Cesarean section. Post-operatively the patient's ICP and jugular venous saturation were monitored in the intensive care unit. RESULTS: The patient delivered a 1185 g infant who did well. The patient's ICP was well controlled until the tenth post-operative day when she developed malignant brain edema and died. CONCLUSION: This case highlights three important points. First, simultaneous craniotomy and Cesarean section can be performed. Second, intraoperative control of bleeding Moyamoya vessels is described. Third, the difficult post-operative management of these cases is highlighted. The literature regarding Moyamoya disease and pregnancy is reviewed and some recommendations for the management of this rare but potentially deadly condition are presented.

Adult↗
PubMed2000

Post-exposure chemoprophylaxis (PECP) against SIV infection of macaques as a model for protection from HIV infection.

We report that simian immunodeficiency virus (SIV) infection in macaques is a valuable animal model for studying post-exposure chemoprophylaxis (PECP). PECP with the acyclic nucleoside reverse transcriptase inhibitors 9-(2-phosphonylmetho-xyethyl)adenine (PMEA) and (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) at early viral infection can provide long-term protection against subsequent heterologous SIV challenge. Eight macaques previously treated with PECP (called PECP macaques) and four naive controls were challenged intravenously with the most virulent form of SIV, SIV(PBj14). All controls showed signs of SIV(PBj14)-induced acute disease syndrome on days 6 and 7 post-inoculation (PI). One had a fatal viral infection and two surviving controls had persistent infection and decreased CD4+ cell count. Virologic studies of the three surviving controls revealed SIV in multiple lymphoid tissues and peripheral blood mononuclear cells (PBMCs) at necropsy. In contrast, the PECP macaques showed none to mild signs of acute disease syndrome at day 9 PI and exhibited only transient SIV infection in PBMCs between weeks 1 and 8 PI. In virologic studies of five PECP macaques necropsied, two macaques were SIV-negative and the other three were SIV-positive only in either lymph node or bone marrow. Three SIV(PBj14)-challenged PECP macaques, that were randomly reserved for a follow-up study for > 4.0 years PI showed extremely low to undetectable levels of PBMC-associated viremia and normal to increased levels of CD4 + and CD8 + cell counts throughout the study. Our results indicate that early PECP could activate immune responses to protect against subsequent infection with heterologous challenge virus.

Adenine↗
PubMed2000

Cervical myelocystoceles and meningoceles: long-term follow-up.

Little is known about the long-term prognosis of patients with cervical myelocystoceles and meningoceles. In this study, we report the long-term follow-up (average 10 years and 8 months) of 8 patients with cervical myelocystoceles and meningoceles. Neurologic, orthopedic, urologic and psychosocial status was assessed on long-term follow-up. The results indicate that in patients with cervical myelocystoceles, neurologic deficits become noticeable in the first year of life as the infant matures. Motor deficit was common in these patients, whereas sensory and urologic deficits did not occur. We believe that this is related to underlying myelodysplasia. In addition, patients with cervical myelocystoceles tend to have significant orthopedic problems. In contrast, patients with cervical meningoceles do not have neurologic deficits, but do develop mild orthopedic problems.

Adolescent↗
PubMed2000

Traumatically induced lymphangioma of the ulnar nerve. Case report.

Lymphangiomas, benign hamartomatous lesions involving lymphatic tissue, result from a failure of lymphatic channels to communicate with the venous system or normal lymphatic channels. The authors describe a case in which a lymphangioma arising within the ulnar nerve developed after trauma to the same area. This is the second reported case of a lymphangioma that originated from a peripheral nerve and the first case in which the lesion was associated with trauma. The authors propose that a lymphangioma involving the peripheral nerve may be the result of trauma.

Humans↗
PubMed2000

Spontaneous resolution and recurrence of a Chiari I malformation and associated syringomyelia. Case report.

The spontaneous resolution of syringomyelia has been reported infrequently. In patients with Chiari I malformations, resolution of the syringomyelia has sometimes been associated with improvement of their malformation. The authors present a case of spontaneous resolution followed by recurrence of syringomyelia and a corresponding change in the Chiari malformation. This case is of interest in light of the theories postulated to explain spontaneous resolution of syringomyelia.

Arnold-Chiari Malformation↗
PubMed1999

Effect of speech processor program modifications on cochlear implant recipients' threshold and maximum acceptable loudness levels.

This study's purpose was to determine whether or not modifications in speech processor electrical stimulation levels were associated with changes in five Nucleus 22 cochlear implant recipients' thresholds or maximum acceptable loudness levels (MALs). These modifications in minimum and maximum stimulation levels were made to optimize hearing in everyday life. One threshold and one MAL were obtained on each active electrode during six, weekly test sessions, three before and three after program modification. Only one participant had a significant change in threshold after program modification; this participant and four others had significant changes in MAL. Participants' threshold variability was the same, but MAL variability was higher than that observed in other studies. Because these participants had no experience making MAL judgments prior to this study, this result suggests that implant recipients should be given sufficient practice in making MAL judgments to provide a stable clinical estimate of the upper boundary of the electrical dynamic range.

Acoustic Stimulation↗
PubMed1998

Optimization of speech processor fitting strategies for Chinese-speaking cochlear implantees.

OBJECTIVES: To compare speech recognition performance in Chinese-speaking cochlear implant patients with a speech processor program selected by the clinical audiologist in Taiwan and with a new speech processor program based on the Washington University clinical procedure developed by Skinner et al. STUDY DESIGN: Six adult Chinese-speaking patients implanted with the Nucleus cochlear implant system participated in this study. METHODS: A fitting procedure developed in 1995 by Skinner et al. at Washington University School of Medicine was used to create a new speech processor program to optimize each patient's hearing in everyday life. Speech tests (vowels, consonants, tones, and words), sound-field thresholds, and a self-report questionnaire were used to evaluate each patient's performance with his or her previous speech processor program and a new one. RESULTS: Four of the six patients had significant changes from the previous to the new speech processor program. These changes were associated with improvement in score on at least one speech test, more sensitive sound field thresholds, and reported improvement in some everyday listening situations on the questionnaire. CONCLUSIONS: These results suggest that use of this procedure with adult cochlear implantees may improve benefit in everyday life. Analysis of the speech test stimuli and patients' responses provides a basis for modification or creation of new Mandarin Chinese speech tests for preoperative and postoperative evaluation of adult cochlear implant patients.

Adolescent↗
PubMed1997

Marginal leakage of amalgam restorations pretreated with various liners.

PURPOSE: To evaluate and compare the microleakage of amalgam restorations lined with four different liners. MATERIALS AND METHODS: Cylindrical occlusal cavities were prepared in extracted human molars and the teeth were then divided into four groups and lined with one of four liners: Amalcoden, AM (glass-metal ionomer), FujiDuet, FD (glass ionomer), Amalgambond, AB (adhesive resin), or copal varnish, CV. Each cavity was then restored with a high-copper amalgam alloy and aged for 7 days in 37 degrees C distilled water. The specimens were then thermocycled for 300 cycles followed by immersion in 0.5% basic fuchsin dye solution for 24 hours. The teeth were then embedded in resin, sectioned, and dye penetration at the tooth/amalgam interface evaluated microscopically at x 100 and scored from 0 to 4 (0 = no leakage and 4 = greatest leakage). RESULTS: The median values were: AM = 1.0; FD = 0.5; AB = 1.1; and CV = 4.0. Statistical analysis using Kruskal-Wallis and Mann-Whitney U indicated no significant differences between AM and AB or FD and AB. CV was however, significantly worse at P < 0.01.

Dental Amalgam↗
PubMed1995

Tibial mononeuropathy from a lower limb synovial cyst.

BACKGROUND: Tibial mononeuropathy due to compression by a synovial cyst is uncommon with fewer than 10 cases reported in the literature. METHOD: Case Study. RESULTS: Tibial motor mononeuropathy with focal conduction block between the popliteal fossa and ankle was identified by electrophysiological testing. Magnetic resonance imaging and surgical exploration identified a synovial cyst compressing the nerve just distal to the popliteal fossa. CONCLUSIONS: The combination of electrophysiological localization and imaging in cases of unexplained tibial mononeuropathy may identify an unexpected structural cause.

Adult↗
PubMed1994

Effects of blood-volume distribution on the characteristics of the carotid baroreflex in humans at rest and during exercise.

Seven supine subjects were studied at rest and during mild to moderate dynamic leg exercise with and without unloading of the cardiopulmonary baroreceptors accomplished by exposing the lower portion of the body to a subatmospheric pressure of 20 mmHg (Lower Body Negative Pressure, LBNP). The function of the cardiac branch of the carotid baroreflex was studied over its full operational range by measuring R-R intervals during application of pulse synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) induced increasing R-R intervals in all conditions. In conformity with previous results from our laboratories it was found that the maximal rate of change in relative R-R intervals and the corresponding transmural pressure were higher during exercise than at rest, indicating that exercise increased the carotid baroreflex sensitivity and shifted its optimal buffering range to higher arterial pressures. LBNP did not affect the characteristics of the reflex at rest nor during exercise. It is concluded that reduced central venous pressure with consequent selective cardiopulmonary receptor disengagement exerts no influence on the carotid baroreflex control of heart rate (HR), as tested over the entire arterial pressure-effector response relation, either at rest or during mild-moderate exercise.

Adult↗
PubMed1994

Shivering thermogenesis during acute hypercapnia.

The effects of acute hypercapnia on human thermoregulation during cold exposure were investigated by immersion of eight male subjects to the neck in a 15 degrees C water bath until their core temperatures dropped to 35 degrees C or until 1 h of immersion had elapsed. Air was inspired throughout each experiment, with the exception of a 15-min period commencing with the attainment of an esophageal temperature (Tes) of 36.5 degrees C, during which subjects inspired a gas mixture containing 4% CO2, 20% O2, and 76% N2. Oxygen uptake (VO2, L.min-1), inspired minute ventilation (Vi, L.min-1), esophageal temperature (Tes, degrees C), rectal temperature (Tre, degrees C), mean unweighted skin temperature (Tsk, degrees C), mean heat flux (Q, W.m-2), and electromyographic activity (EMG, mV) of the trapezius and masseter muscles were recorded continuously. VO2 and integrated EMG activity (IEMG) were used as the primary indicators of shivering thermogenesis. Shivering EMG was attenuated immediately following the switch of the inhaled gas mixture from air to 4% CO2. For both the masseter and trapezius muscles the IEMG was significantly suppressed (p < 0.05) during the hypercapnic period. The IEMG values preceding the switch to the hypercapnic mixture were 15% greater than those during the CO2 period. Similarly, IEMG values in the post-CO2 period were 55% greater than during the CO2 period. It is concluded that acute periods of hypercapnia during cold exposure may result in transient suppression of shivering tremor, but this does not appear to affect thermal balance, as reflected in the absence of any significant effect on Tes.

Acute Disease↗
PubMed1994

Is the older ear more susceptible to noise damage?

Eight chinchillas aged 8.9 to 12.8 years were used to examine the effect of noise on the aging ear. The left malleus/incus complex was removed to produce a 50-dB conductive hearing loss which protected those ears from noise damage. The animals were then exposed for 36 days to an octave band of noise with a center frequency of 0.5 kHz and a sound pressure level of 95 dB. After 1 hour (n = 2) or 1 month (n = 6) of recovery, their cochleas were prepared for microscopic examination. The percentages of missing inner hair cells (IHCs) were 7.4 +/- 6.0% and 7.8 +/- 5.1% for their protected and exposed ears, respectively. Outer hair cell (OHC) loss was 12.8 +/- 8.7% and 20.6 +/- 7.8% for their protected and exposed ears, respectively. A paired sample Student's t test revealed that OHC loss was significantly greater (P = .003) in the older-exposed compared to the older-protected ears whereas IHC loss was not significantly different. For younger-exposed ears (i.e., 1 to 3 years), the percentages of missing IHCs and OHCs averaged 2.6 +/- 2.0% and 12.3 +/- 4.6%, respectively. When the aging-related cell loss was subtracted from total loss in the younger- and older-exposed ears, the noise-induced loss of sensory cells in the older ears was not significantly different from that in the younger ears. Therefore, it is concluded that older chinchilla ears are not more susceptible to noise damage than younger ears.

Aging↗
PubMed1993

Autonomic nervous control of heart rate during blood-flow restricted exercise in man.

Power spectra of instantaneous heart rate (fc) allows the estimation of the contribution of sympathetic and parasympathetic control of fc during steady-state conditions. The present study was designed to examine autonomic control of fc as influenced by normal dynamic leg exercise and by ischemic leg exercise. Eight subjects performed supine cycle ergometry at 30% of their control peak work rate, with and without blood-flow restriction. Blood-flow restriction was induced by exposing the exercising legs to a supra-atmospheric pressure of 6.7 kPa (leg positive pressure; LPP). The exercise responses of arterial pressure and fc increased (P < 0.05) by LPP exposure. The exaggerated pressor response may be attributed to a chemoreflex drive originating in the ischemic muscles. Exposure to LPP during exercise also produced a significant decrease in parasympathetically mediated high frequency (HF; 0.15-1.00 Hz) fluctuation of fc, as indicated by a decrease (P < 0.05) in percent HF power compared to the control exercise level. During LPP exercise, the sympathetically mediated very low frequency (VLF; 0-0.05 Hz) fluctuation of fc increased, as indicated by an increase (P < 0.05) in percent VLF power above control exercise levels. Both LPP and control exercise conditions decreased (P < 0.05) power in all frequency ranges of interest compared to their respective resting conditions. The results suggest that the increase in fc associated with normal dynamic exercise was mediated predominantly by parasympathetic withdrawal, whereas the exaggerated fc response during ischemic exercise resulted from a combination of cardiac sympathetic drive and parasympathetic withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗