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Biomedical subjects

J C Han

Publications and source records attributed to J C Han.

At least 19 recordsLinked to original sources
PubMed2001

Recent developments in turbine blade internal cooling.

This paper focuses on turbine blade internal cooling. Internal cooling is achieved by passing the coolant through several rib-enhanced serpentine passages inside the blade and extracting the heat from the outside of the blades. Both jet impingement and pin-fin-cooling are also used as a method of internal cooling. In the past number of years there has been considerable progress in turbine blade internal cooling research and this paper is limited to reviewing a few selected publications to reflect recent developments in turbine blade internal cooling.

Journal Article↗
PubMed1999

Endoscopic/Microscopic approach to sphenopetroclival complex: an anatomical study.

A dilemma presents itself to the otoneurologist and neurosurgeon when determining the least invasive surgical approach to giant cholesterol cysts (GCC) of the petrous apex of the temporal bone. These lesions can be diagnosed with a fair degree of certainty with imaging studies. Transmastoid and subcochlear approaches may be inadequate to access these lesions, and the transcochlear approach results in the sacrifice of hearing. A minimally invasive, combined microscopic and endoscopic sublabial transsphenoid approach to drain and marsupalize these lesions has been chosen by the authors in those cases that are anatomically possible. The purpose of this article is to establish the feasibility of exenterating anterior petrous apex cells by way of this approach, and to better conceptualize the anatomy of the Spheno-Petro-Clival Complex (SPC). Ten Fresh cadaveric "whole head" specimens were dissected with, endoscopic/microscopic control, through midline, sublabial, transseptal, and transsphenoidal routes to the petrous apex. The three-dimensional relationships of the sphenoid sinus, petrous apex, and the clivus were further demonstrated by dissections of the same specimens from the posterior fossa. Sagittal cut sections were also performed. After confirming the feasibility of this approach by dissections, the technique was adopted for performing drainage of GCC of the petrous apex in clinical cases.

Journal Article↗
PubMed1997

Altered regulation of cell surface peptidases in human cholesteatoma.

Cholesteatoma is a destructive process involving an accumulation of desquamated keratin arising from squamous epithelium that pathologically has invaded the middle ear or mastoid process. The clinical hallmarks of cholesteatomas, namely invasion of healthy tissues, migration, unrestrained proliferation, aggressiveness, recidivism, and uncoordinated differentiation predict the existence of defects in the normal biology and biochemistry of the cellular constituents that compose a cholesteatoma, as well as in the cellular interactions between these cells, the surrounding normal tissue, and the host. In the current report, we analyzed 11 cholesteatomas and matched healthy tissue for altered expression in four different cell surface peptidases, aminopeptidase A, aminopeptidase N, dipeptidyl peptidase IV, and neutral endopeptidase. We suggest that peptidases may modulate cell growth and differentiation by inactivating stimulatory signals (or conversely, by activating inhibitory signals).

Adolescent↗
PubMed1996

Pediatric cholesteatoma: an individualized, single-stage approach.

We report our experience with a one-stage surgery for pediatric cholesteatoma in 216 ears. Our technique is based on three main principles: (1) the surgery is individualized; (2) the goal of surgery is to completely remove cholesteatoma and related disease in one operation; and (3) the reconstruction is performed to provide both good hearing and a dry, trouble-free ear. The incidence of recidivism was 10.2%, and the rate achieved was 13.3% at 5 years and 24% at 10 years. Canal wall down surgery was the predominant procedure used. The incidence of intraoperative neurosensory hearing loss, vertigo, and facial nerve injury was extremely low. The postoperative cavity problems encountered were minimal.

Adolescent↗
PubMed1994

A procedure for quantitative determination of tris(2-carboxyethyl)phosphine, an odorless reducing agent more stable and effective than dithiothreitol.

The concentration of tris(2-carboxyethyl)phosphine (TCEP) can be conveniently determined by measuring the amount of 2-nitro-5-thiobenzoate (NTB) formed after reaction with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). This method utilizes the fact that TCEP reduces DTNB rapidly and stoichiometrically to generate two equivalents of NTB which, in its anionic form, has a molar extinction coefficient of 14,150 M-1 cm-1 at 412 nm. This method is sensitive enough to detect the concentration of TCEP in the micromolar range and has proven useful in monitoring the stability or oxidation of TCEP under various conditions. TCEP is not only very stable in acidic solutions, but unlike dithiothreitol (DTT) which readily oxidizes above pH 7.5, it is also highly stable in basic solutions. The rates of reduction of DTNB by TCEP and DTT are compared in the pH range 6-9. Below pH 8, TCEP is significantly more effective than DTT in reducing this disulfide. The rates of reduction of 2,2'-dithiodipyridine (2,2'-DTDP) by TCEP and DTT are compared in the pH range 1.5-8.5. Unlike DTT which is totally inactive at pH 1.5, TCEP is still capable of reducing 2,2'-DTDP effectively at this pH. Thus, if TCEP and thiols are simultaneously present, the concentration of TCEP can be selectively determined by using 2,2'-DTDP at very low pH.

Dithionitrobenzoic Acid↗
PubMed1994

Microfiberoptic evaluation of the middle ear cavity.

Endoscopic instruments have revolutionized surgical diagnosis and treatment. Recently, a high resolution microfiberoptic endoscope has been developed that has vast potential for otologic use. This microfiberoptic endoscope was used in cadaver and human studies to visualize the middle ear cavity. The technique used involved placing a 1.0-mm or smaller microfiberoptic scope into the middle ear via a tympanic membrane perforation, through a myringotomy tube or up the eustachian tube. Using the scope, the mesotympanum and hypotympanum can be well visualized. Similarly, the round window, oval window, ossicular chain, and related structures can be clearly demonstrated and recorded photographically. This technique has great potential to enhance diagnosis without open surgery.

Adolescent↗
PubMed1993

Allicin-induced hypotension in rabbit eyes.

The intent of this work was to examine the actions of allicin on 1) intraocular pressure (IOP) in normal and unilaterally sympathectomized (SX) rabbits; 2) cAMP accumulation in the rabbit iris-ciliary body (ICB) and cultured nonpigmented epithelial (NPE) ciliary body cells; and 3) 3H-norepinephrine (NE) release by calculating fractional tritium overflow in response to electrical field stimulation (EFS, 5 Hz, 12 V/cm) in isolated, perfused rabbit ICBs. Allicin, one of the active compounds produced by garlic, was evaluated on IOP and it was determined that allicin (1, 2.5, or 10 micrograms), topically, but not the precursor, alliin (10 micrograms), lowered the IOP unilaterally in normal rabbits. Allicin (10 micrograms) reduced the IOP by 6 +/- 1 mmHg (n = 4) in normal rabbits at 2 hrs (maximum response) whereas no change occurred in sympathectomized rabbit eyes. Moreover, allicin (0.01, 0.1, or 1 microM) caused 40, 40, or 52% inhibition, respectively, of 3H-NE overflow in response to EFS. Isoproterenol (ISO, 1 microM) stimulated cAMP accumulation by 3.6 and 9 fold in isolated rabbit ICB and cultured NPE cells, respectively. Allicin (1 microM) had no effect on basal cAMP level while it inhibited ISO-stimulated cAMP accumulation by 40% and 23% in ICB and NPE cells, respectively. This study suggests that allicin lowered IOP, in part, by dual actions at the neuroeffector junction.

Animals↗
PubMed1993

Differences in dendritic cells in congenital and acquired cholesteatomas.

Cholesteatomas are histologically benign, though biologically invasive lesions that arise from the migration of squamous epithelium of the ear. Acquired cholesteatomas usually arise in an antigenically active environment, i.e., a chronically and/or recurrently inflamed middle ear. In contrast, congenital cholesteatomas occur in an uninflamed environment. The potential role of dendritic cells (DCs) in the evolution of this lesion has not been thoroughly studied. By staining for S-100 protein, the authors evaluated the presence and distribution of DCs in cholesteatomas. Sixteen cases of cholesteatomas diagnosed from 1987 to 1989 were selected for this study. The formalin-fixed, paraffin-embedded sections were processed by a standard avidin-biotin peroxidase-antiperoxidase method for S-100 protein and for leukocyte common antigen (LCA). The presence and distribution of S-100 protein-positive DCs was evaluated and compared to canal wall skin. DCs were present in all cases. Nine acquired cholesteatomas had 5 to 16 epithelial DCs per high-power field (HPF). Seven congenital cholesteatomas were examined. Four with isolated congenital pearl-like cholesteatomas had 1 to 3/HPF epithelial DCs. In contrast, the three inflamed congenital cholesteatomas had 6 to 12/HPF DCs. The control uninflamed canal wall skin had only 1 to 3/HPF DCs. All DCs were LCA negative, as expected.

Adolescent↗
PubMed1993

Alteration in cholesteatoma fibroblasts: induction of neoplastic-like phenotype.

Cholesteatomas are invasive, locally destructive skin-like lesions that, after operative removal, have a significant recidivistic rate. These aggressive characteristics suggest a fundamental alteration in the biology of one or more of its constituents (i.e., keratinocytes, fibroblasts, and inflammatory cells). The cholesteatoma matrix was studied by subculturing it into its main cellular components. Short-term cell cultures of fibroblasts from cholesteatoma matrix and controls from ear canal and postauricular skin were established. These cultured fibroblasts were tested for invasiveness using the Boyden Chamber Assay of Albini. The cells were evaluated for their ability to migrate, attach to, and invade a basement membrane. Results of the motility and attachment of fibroblasts cultured from cholesteatoma, canal wall, and postauricular skin did not differ. However, fibroblasts from 12 of 12 cholesteatoma specimens were highly invasive, while those from postauricular and ear canal skin were either weakly invasive or not invasive. This represents the first report of an intrinsic defect in the biology of cholesteatoma. Invasive fibroblasts that demonstrate a loss of growth control, may provide a contact guidance mechanism that aggressively mobilizes the squamous keratinizing epithelium contributing to the invasive, aggressive behavior of cholesteatoma.

Adolescent↗
PubMed1992

Surgery for recurrent and residual cholesteatoma.

One hundred twelve patients (116 ears) were treated for recurrent and residual cholesteatoma. A retrospective review revealed that 66% had undergone canal wall down mastoidectomy at the previous surgery. The surgical procedure at revision was selected on the basis of an intraoperative assessment of the extent of disease, and clinical prediction of eustachian tube function. The average period of follow-up was 3.4 years. Revision surgery was successful in providing the patient with a safe, dry ear in 105 (91%) of 116 cases. Surgical principles and hearing results are presented.

Adult↗
PubMed1991

Management of labyrinthine fistulas caused by cholesteatoma.

The surgical management of labyrinthine fistulas caused by cholesteatoma remains controversial. Forty cases (41 ears) of labyrinthine fistulas were reviewed. This represented 10% of our total series of cholesteatomas in adults and children (426 ears). Clinical presentation, extent of disease, results of fistula testing and audiometric studies, and radiographic findings were analyzed. A canal wall-down procedure was performed in all but one patient. Generally an attempt was made to completely remove the cholesteatoma, to graft the fistulous area, and to reconstruct the middle ear mechanism in one stage. The matrix was preserved in patients with large fistulas where the involved ear was the only hearing one, when the matrix was adherent to the underlying optic duct, and in selected elderly persons. Long-term followup did not reveal a significant difference in hearing, degree of vertigo, or incidence of recidivism when those patients in whom the matrix was removed were compared with those in whom the matrix was preserved. The importance of recognizing the presence of a labyrinthine fistula preoperatively is stressed, along with the need to be prepared for an unexpected fistula. Operative management is described.

Adolescent↗
PubMed1989

Acquired cholesteatoma in the pediatric age group.

Successful treatment of cholesteatoma in children is based on the same principles of therapy used in adults. A clinical profile of children with acquired cholesteatoma is compared with that of adults. Issues related to aggressiveness of disease, pathophysiology, diagnostic problems, and treatment approaches are discussed.

Adolescent↗
PubMed1989

Management of congenital pediatric cholesteatomas.

During the past 10 years discrete middle ear congenital cholesteatomas have been detected with greater frequency in young children. The increased recognition of this condition is probably related to the pediatricians' greater awareness of this defect, their improved facility with pneumatic otoscopy, and effective audiometric and tympanometric screening procedures. This early detection while the lesions are small and localized facilitates their surgical removal. Clinically, it would appear that congenital cholesteatomas can be subdivided into two categories according to their anatomic locations. The anterior lesions present as an isolated pearl that arise from an area on the anterior surface of the malleus, are usually associated with normal hearing, and have pneumatized mastoids. The posterior lesions do not seem to originate from a clearly defined anatomic area, have a higher incidence of sclerotic mastoids, and erode the ossicular chain commonly producing a hearing loss. The anterior middle ear cholesteatoma probably arises from a persistent epidermoid formation, a structure that normally is present during fetal development of involutes by the 33rd week of gestation. The origin of cholesteatomas arising in the posterior middle ear space remains more controversial.

Adolescent↗
PubMed1988

Digital filtering and spectral analysis of the low intensity ABR.

Spectral analysis along with zero and standard-phase shift digital filtering were performed on evoked potentials recorded from 12 normal hearing subjects. The results indicated a progressive shifting of the mean spectral content of the ABR toward the low frequencies as the stimulus intensity was lowered. Despite this, the effects of zero-phase shift high-pass digital filtering at 100 Hz (36 dB/oct) did not significantly differ between waveforms elicited by a 75 dB nHL, 55 dB nHL, and 35 dB nHL stimulus. The major response frequency of the ABR is related to the distance between the peak (IV/V) and the following major trough (approximates one-half the response period). In waveforms where the major trough occurred before 10 msec, the use of 100 Hz, 36 dB/oct, zero-phase shift high-pass filters produced only a small reduction in response amplitude, even at low stimulus intensity levels. Waveforms which had a major trough (Na1) between 10 to 15 msec were reduced in amplitude by 100 Hz, 36 dB/oct, zero-phase shift high-pass filters (the longer period of the response energy in these waveforms corresponds to a lower energy frequency). However, this trough has a latency that prevents it from being recorded on a 10 msec time base or defined as an ABR. Based on these results, the use of zero-phase shift high-pass filters with a high-pass cutoff frequency that is equal to or less than the resolution of the time base (1/time base) appears to be a desirable method of reducing muscle artifact and other electrical contamination of the ABR.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1979

Residue studies with [14C]fosamine ammonium in channel catfish.

The active ingredient in du Pont Krenite brush control agent is ammonium ethyl carbamoylphosphonate (fosamine ammonium salt, formerly known as DPX-1108). Residues in channel catfish exposed to 1.1 ppm 14C-carbonyl-labeled fosamine ammonium in water for 4 wk were found to plateau in 2-3 wk with an accumulation factor (ratio of residue in fish to residue in water) of less than 1. In a separate experiment channel catfish were placed for 4 wk in a tank containing [14C]fosamine ammonium-treated soil (15 ppm) that had been aged for 30 d prior to flooding and initiation of fish exposure. The residue levels in this latter group of catfish also plateaued in 2-3 wk with an accumulation factor of less than 1. In both experiments, after the 4-wk exposures, the fish were transferred to fresh water for 2-wk depuration periods, during which residue levels dropped 50--90%. No effects on the fish were observed during these experiments.

Animals↗