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Biomedical subjects

H A Jenkins

Publications and source records attributed to H A Jenkins.

At least 37 records · Page 2Linked to original sources
PubMed1995

Radiation therapy in the management of paragangliomas of the temporal bone.

The use of radiation therapy for the treatment of paragangliomas of the temporal bone remains controversial. Few studies exist that provide sufficient information on staging the long-term follow-up to clarify this issue. A retrospective study was undertaken of 38 patients with temporal bone paragangliomas treated with radiation therapy between 1956 and 1991. All patients received radiation therapy, either as a primary modality (14 patients), in combination treatment with surgery (13 patients), or as salvage therapy (11 patients). Mean disease stage (Fisch classification system) for each group was C2, B, and C1, respectively. The follow-up period ranged from 1 to 27 years (median 11.5 yr). Local control was achieved in 79% of the primary radiation therapy group, 100% of the combined treatment group, and 91% of the salvage therapy group. Complications resulting from radiation therapy were few and minor. This study demonstrates that the use of radiation therapy for temporal bone paragangliomas offers effective local control as a primary treatment modality, in combination with surgery, and as salvage therapy with few long-term complications.

Adult↗
PubMed1994

Intralabyrinthine schwannoma.

Intralabyrinthine schwannoma is a rare tumor. Until the present time, the diagnosis, for the most part, has been made either incidentally during labyrinthectomy or described as a pathologic finding during temporal bone histologic studies. This article presents a patient with long-standing dysequilibrium and hearing loss due to an intralabyrinthine schwannoma. Diagnosis was made on the basis of a magnetic resonance imaging with gadolinium prior to surgery and confirmed pathologically on excision.

Adult↗
PubMed1994

alpha-Difluoromethylornithine delays behavioral recovery and induces decompensation after unilateral labyrinthectomy.

Biochemical and pharmacologic studies suggest a role for the ornithine decarboxylase-polyamine system as a modulator of behavioral changes during vestibular compensation. alpha-Difluoromethylornithine specifically blocks the rate-limiting step of polyamine biosynthesis. To assess the effects of alpha-difluoromethylornithine on the acute phase of postural compensation, guinea pigs were divided into groups subjected to either unilateral labyrinthectomy only (n = 7), alpha-difluoromethylornithine (500 mg/kg/day) for 4 days before labyrinthectomy (n = 10), equivalent volumes of saline for 4 days before labyrinthectomy (n = 8), and sham operations (n = 5). Yaw head tilt and roll head tilt, trunk curvature, and air-righting reflex were measured at baseline and at regular intervals up to 4 weeks. alpha-Difluoromethylornithine significantly delayed recovery of normal air-righting but had no effect on yaw head tilt, roll head tilt, and trunk curvature. We also evaluated effects of alpha-difluoromethylornithine in compensated guinea pigs. Fully compensated animals from phase 1 were randomly assigned to receive alpha-difluoromethylornithine (500 mg/kg/day) or saline once daily for 4 days. Only 33% of alpha-difluoromethylornithine animals maintained air-righting, compared with 100% of saline-treated animals (p = 0.003). Maximum trunk curvature was greater in the alpha-difluoromethylornithine group (p = 0.02). Thus alpha-difluoromethylornithine not only delayed the time course for postural recovery after unilateral labyrinthectomy, it also transiently disrupted the maintenance of the compensated state.

Animals↗
PubMed1994

Histopathology of temporal bone fractures: implications for cochlear implantation.

Temporal bone fractures often cause loss of audiovestibular function. Those patients with bilateral profound sensorineural hearing losses secondary to temporal bone fractures become candidates for cochlear implantation. The authors present the histopathology of five temporal bone fractures in three patients, evaluating specifically the traumatic effects on the neural elements of the inner ear. Transverse fractures of the temporal bone result in severe loss of hair cells, ganglion cells, and other supporting cells in the inner ear. Occasionally labyrinthitis ossificans may occur as a consequence of trauma or infection. While longitudinal fractures do not violate the otic capsule, these same neural elements may be damaged by concussion.

Adult↗
PubMed1993

Glucose and glutamine metabolism of a murine B-lymphocyte hybridoma grown in batch culture.

The energy metabolism of a mammalian cell line grown in vitro was analyzed by substrate consumption rates and metabolic flux measurements. The data allowed the determination of the relative importance of the pathways of glucose and glutamine metabolism to the energy requirements of the cell. Changes in the substrate concentrations during culture contributed to the changing catalytic activities of key enzymes, which were determined. 1. A murine B-lymphocyte hybridoma (PQXB1/2) was grown in batch culture to a maximum cell density of 1-2 x 10(6) cells/mL in 3-4 d. The intracellular protein content showed a maximum value during the exponential growth phase of 0.55 mg/10(6) cells. Glutamine was completely depleted, but glucose only partially depleted to 50% of its original concentration when the cells reached a stationary phase following exponential growth. 2. The specific rates of glutamine and glucose utilization varied during culture and showed maximal values at the midexponential phase of 2.4 nmol/min/10(6) cells and 4.3 nmol/min/10(6) cells, respectively. 3. A high proportion of glucose (96%) was metabolized by glycolysis, but only limited amounts by the pentose phosphate pathway (3.3%) and TCA cycle (0.21%). 4. The maximum catalytic activity of hexokinase approximates to the measured flux of glycolysis and is suggested as a rate-limiting step. In the stationary phase, the hexokinase activity reduced to 11% of its original value and may explain the reduced glucose utilization at this stage. 5. The maximal activities of two TCA cycle enzymes were well above the measured metabolic flux and are unlikely to pose regulatory barriers. However, the activity of pyruvate dehydrogenase was undetectable by spectrophotometric assay and explains the low level of flux of glycolytic metabolites into the TCA cycle. 6. A significant proportion of the glutamine (36%) utilized by the cells was completely oxidized to CO2. 7. The measured rate of glutamine transport into the cells approximated to the metabolic flux and is suggested as a rate-limiting step. 8. Glutamine metabolism is likely to occur via glutaminase and amino transaminase, which have significantly higher activities than glutamate dehydrogenase. 9. The calculated potential ATP production suggests that, overall, glutamine is the major contributor of cellular energy. However, at the midexponential phase, the energy contribution from the catabolism of the two substrates was finely balanced--glutamine (55%) and glucose (45%).

Adenosine Triphosphate↗
PubMed1993

Prospective study of resident-performed stapedectomy.

Because of the diminishing number of patients diagnosed with otosclerosis, the adequacy of residency training in stapedectomy techniques remains controversial. A prospective study, conducted from 1986 to 1991, assessed whether or not surgical outcome obtained by residents, under close supervision by otologic faculty, could be improved using a single stapedectomy technique. Comparison of pre- and postoperative hearing results (pure-tone averages of 500, 1000, and 2000 Hz) from 49 cases revealed closure of the air-bone gap to within 10 dB in 68 percent of procedures. Complications included failure to improve the conductive hearing loss, tympanic membrane perforations, transient facial nerve weakness, subluxation of the incus, and adhesions. The failure to improve the success rate in resident-performed procedures relates to the individual learning curve and the limited number of training cases.

Audiometry, Pure-Tone↗
PubMed1992

Histopathology of the temporal bone following multichannel cochlear implantation.

The temporal bone histopathologic findings of a patient having received a Nucleus 22-channel cochlear implant (Cochlear Corp, Englewood, Colo) following bilateral transverse otic capsule fractures is presented. The case was complicated by perilymph fistulas, labyrinthitis, meningitis, and death due to drowning. The left cochlea revealed complete labyrinthitis ossificans; the implanted right cochlea demonstrated new bone formation in the basal turn of the scala tympani, degeneration of the organ of Corti, but normal ganglion cell counts. Results of psychophysical and speech perception 4 months after implantation are presented.

Adult↗
PubMed1992

Characterization of glutamine metabolism in two related murine hybridomas.

Aspects of glutamine metabolism were examined in two related hybridomas, a high-producing line (PQX B1/2) and a low-producing line (PQX B2/2). The growth and metabolic characteristics of both cell lines were identical or very similar. During batch growth glutamine was completely exhausted from the medium and an examination of the fate of [14C]glutamine highlighted the importance of this amino acid as an energy source. The relative enzyme activities and the amount of ammonia produced during growth indicated that glutamine is oxidized preferentially via the transamination pathway. The overall rate of glutamine utilization from the growth medium was similar to the rate of [14C]glutamine uptake which suggests that transport may regulate glutamine metabolism.

Animals↗
PubMed1992

Hearing preservation in acoustic neuroma surgery.

With advances in imaging, intracanalicular acoustic neuromas are identified readily in patients including, oftentimes, those with serviceable hearing. Fourteen patients were operated on in an attempt to preserve hearing. Hearing was retained in 10 (71%) of the 14. Serviceable hearing was present in 7 (50%), borderline serviceable hearing in 2 (14%), and nonserviceable hearing in 1 (7%). The problems, advantages, and disadvantages of the differing approaches are discussed.

Adolescent↗
PubMed1992

Temporal bone histopathology of a patient with a nucleus 22-channel cochlear implant.

The temporal bone histopathology of a patient with profound sensorineural hearing loss attributable to cochlear otosclerosis is presented. The patient had a Nucleus 22-channel cochlear prosthesis implanted in the right ear prior to his demise. Unintentional scala media insertion of the electrode array resulted from labyrinthitis ossificans obliteration of the scala tympani. Inadvertent facial nerve stimulation necessitated program exclusion of electrodes 11 to 16 located in proximity to the labyrinthine and geniculate segments of the facial nerve. The patient received significant benefit from use of the device. The histopathologic findings are correlated with psychophysical and speech perception results.

Cochlear Diseases↗
PubMed1991

Positional envelope as a response parameter in caloric testing.

Bithermal caloric testing was carried out in 57 normal subjects and 374 patients presenting with subjective complaints of vertigo over a 4-year period from December 1984 to December 1988. Responses were quantitatively assessed using a DEC PDP 11/73 laboratory minicomputer. Patients were classified as normal and abnormal according to caloric responses based on standard methods of calculating unilateral hypoexcitability and directional preponderance using the maximum slow component velocity. Results obtained from the slow component velocity for unilateral hypoexcitability and directional preponderance were compared to the same values obtained from the overall positional envelope calculated by an integration of the slow component velocity vs. time curve. Although duration of nystagmus varies extensively in normal subjects and has not proven clinically useful in identifying abnormalities, the integral of response amplitude over time gives a more complete description of the vestibular response. However, when compared to the maximum slow component velocity in abnormal patients, the positional envelope identified only 94 of the total 119 abnormalities (79%). Therefore, maximum slow component velocity is the more sensitive response parameter in identifying vestibular pathology.

Algorithms↗
PubMed1991

Vestibular testing in hearing loss.

The basic electonystagmography battery (saccade, gaze, position, caloric tests, and spontaneous nystagmus) are described along with rotational testing and dynamic posturography. Emphasis is placed on interpretation, relative benefits, and limitations as an aid in diagnosis.

Caloric Tests↗
PubMed1990

The diagnostic dilemma of otosyphilis. A new western blot assay.

Currently, the diagnosis of otosyphilis applies to any patient with otologic symptoms of unknown cause and a positive fluorescent treponemal antibody-absorption (FTA-ABS) test result. However, the FTA-ABS assay can have false-positive results and does not distinguish between active and treated disease. The VDRL test, which has been used to distinguish inactive disease, frequently yields negative results in patients who are nonetheless given the diagnosis of otosyphilis. A new Western blot assay can eliminate the possibility of a false-positive result and can confirm whether the infection is active. This assay was used to diagnose unsuspected active syphilis in a patient believed to have autoimmune ear disease. In three other cases of suspected otosyphilis, the diagnosis was refuted when the Western blot demonstrated that the FTA-ABS result was false-positive or that the infection was inactive.

Adult↗