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Biomedical subjects

K Whang

Publications and source records attributed to K Whang.

16 recordsLinked to original sources
PubMed2001

Laparoscopic Heller myotomy relieves dysphagia in patients with achalasia and low LES pressure following pneumatic dilatation.

BACKGROUND: Although pneumatic dilatation is said to relieve dysphagia in achalasia if it decreases lower esophageal sphincter (LES) pressure to 10 mmHg (n = 23); group C, no previous balloon dilatation and LES pressure >10 mmHg (n = 25). All patients underwent a laparoscopic Heller myotomy and Dor fundoplication. The severity of dysphagia was gauged on a scale of 0-4. RESULTS: In group A, LES pressure was 7 +/- 2 mmHg preoperatively and 8 +/- 3 mmHg postoperatively; the dysphagia score was 3.3 +/- 0.7 preoperatively and 0.9 +/- 1.1 postoperatively. Eighty-nine percent of patients had excellent or good results. In group B, LES pressure was 23 +/- 8 mmHg preoperatively and 10 +/- 1 mmHg postoperatively; the dysphagia score was 3.3 +/- 0.7 preoperatively and 0.3 +/- 0.5 postoperatively. All patients had excellent or good results. In group C, LES pressure was 23 +/- 11 mmHg preoperatively and 14 +/- 12 mmHg postoperatively; the dysphagia score was 3.6 +/- 0.6 preoperatively and 0.2 +/- 0.5 postoperatively. All patients had excellent or good results. CONCLUSIONS: These results show that (a) a LES pressure of <10 mmHg after pneumatic dilatation does not guarantee relief of dysphagia, and (b) laparoscopic Heller myotomy relieves dysphagia in most patients with a postdilatation LES pressure <10 mmHg. Thus, a laparoscopic Heller myotomy is indicated if dilatation does not relieve dysphagia, even if LES pressure has been decreased to <10 mmHg. Esophagectomy should be reserved for the occasional failure of this simpler operation.

Adolescent↗
PubMed2001

Functional magnetic resonance imaging of visual object construction and shape discrimination : relations among task, hemispheric lateralization, and gender.

We studied the brain activation patterns in two visual image processing tasks requiring judgements on object construction (FIT task) or object sameness (SAME task). Eight right-handed healthy human subjects (four women and four men) performed the two tasks in a randomized block design while 5-mm, multislice functional images of the whole brain were acquired using a 4-tesla system using blood oxygenation dependent (BOLD) activation. Pairs of objects were picked randomly from a set of 25 oriented fragments of a square and presented to the subjects approximately every 5 sec. In the FIT task, subjects had to indicate, by pushing one of two buttons, whether the two fragments could match to form a perfect square, whereas in the SAME task they had to decide whether they were the same or not. In a control task, preceding and following each of the two tasks above, a single square was presented at the same rate and subjects pushed any of the two keys at random. Functional activation maps were constructed based on a combination of conservative criteria. The areas with activated pixels were identified using Talairach coordinates and anatomical landmarks, and the number of activated pixels was determined for each area. Altogether, 379 pixels were activated. The counts of activated pixels did not differ significantly between the two tasks or between the two genders. However, there were significantly more activated pixels in the left (n = 218) than the right side of the brain (n = 161). Of the 379 activated pixels, 371 were located in the cerebral cortex. The Talairach coordinates of these pixels were analyzed with respect to their overall distribution in the two tasks. These distributions differed significantly between the two tasks. With respect to individual dimensions, the two tasks differed significantly in the anterior--posterior and superior--inferior distributions but not in the left--right (including mediolateral, within the left or right side) distribution. Specifically, the FIT distribution was, overall, more anterior and inferior than that of the SAME task. A detailed analysis of the counts and spatial distributions of activated pixels was carried out for 15 brain areas (all in the cerebral cortex) in which a consistent activation (in > or = 3 subjects) was observed (n = 323 activated pixels). We found the following. Except for the inferior temporal gyrus, which was activated exclusively in the FIT task, all other areas showed activation in both tasks but to different extents. Based on the extent of activation, areas fell within two distinct groups (FIT or SAME) depending on which pixel count (i.e., FIT or SAME) was greater. The FIT group consisted of the following areas, in decreasing FIT/SAME order (brackets indicate ties): GTi, GTs, GC, GFi, GFd, [GTm, GF], GO. The SAME group consisted of the following areas, in decreasing SAME/FIT order : GOi, LPs, Sca, GPrC, GPoC, [GFs, GFm]. These results indicate that there are distributed, graded, and partially overlapping patterns of activation during performance of the two tasks. We attribute these overlapping patterns of activation to the engagement of partially shared processes. Activated pixels clustered to three types of clusters : FIT-only (111 pixels), SAME-only (97 pixels), and FIT + SAME (115 pixels). Pixels contained in FIT-only and SAME-only clusters were distributed approximately equally between the left and right hemispheres, whereas pixels in the SAME + FIT clusters were located mostly in the left hemisphere. With respect to gender, the left-right distribution of activated pixels was very similar in women and men for the SAME-only and FIT + SAME clusters but differed for the FIT-only case in which there was a prominent left side preponderance for women, in contrast to a right side preponderance for men. We conclude that (a) cortical mechanisms common for processing visual object construction and discrimination involve mostly the left hemisphere, (b) cortical mechanisms specific for these tasks engage both hemispheres, and (c) in object construction only, men engage predominantly the right hemisphere whereas women show a left-hemisphere preponderance.

Adult↗
PubMed2001

Laparoscopic Heller myotomy and Dor fundoplication for achalasia: analysis of successes and failures.

BACKGROUND: In the treatment of achalasia, surgery has been traditionally reserved for patients with residual dysphagia after pneumatic dilatation. The results of laparoscopic Heller myotomy have proven to be so good, however, that most experts now consider surgery the primary treatment. HYPOTHESIS: The outcome of laparoscopic myotomy and fundoplication for achalasia is dictated by technical factors. SETTING: University hospital tertiary care center. DESIGN: Retrospective study. PATIENTS AND METHODS: One hundred two patients with esophageal achalasia underwent laparoscopic Heller myotomy and Dor fundoplication. Fifty-seven patients had been previously treated by pneumatic dilatation or botulinum toxin. The design of the operation involved a 7-cm myotomy, which extended 1.5 cm onto the gastric wall, and a Dor fundoplication. Esophagrams, esophageal manometric findings, and video records of the procedure were analyzed to determine the technical factors that contributed to the clinical success or failure of the operation. MAIN OUTCOME MEASURE: Swallowing status. RESULTS: In 91 (89%) of the 102 patients, good or excellent results were obtained after the first operation. A second operation was performed in 5 patients to either lengthen the myotomy (3 patients) or take down the fundoplication (2 patients). Dysphagia resolved in 4 of these patients. The remaining 6 patients were treated by pneumatic dilatation, but dysphagia improved in only 1. At the conclusion of treatment, excellent or good results had been obtained in 96 (94%) of the 102 patients. CONCLUSIONS: These data show that a Heller myotomy was unsuccessful in patients with an esophageal stricture; a short myotomy and a constricting Dor fundoplication were the avoidable causes of residual dysphagia; a second operation, but not pneumatic dilatation, was able to correct most failures; and that the identified technical flaws were eliminated from the last half of the patients in the series.

Adolescent↗
PubMed2001

Functional, dynamic, and anatomic MR urography: feasibility and preliminary findings.

RATIONALE AND OBJECTIVES: The authors assessed the feasibility of using magnetic resonance (MR) urography to acquire functional, dynamic, and anatomic information in human subjects with normal and hydronephrotic kidneys. MATERIALS AND METHODS: In subjects known to have or suspected of having hydronephrosis, split renal filtration fractions were measured with a customized magnetization-prepared, inversion-prepared gradient-recalled echo sequence to determine the T1 of flowing blood in the inferior vena cava and aorta before and after contrast medium administration and in the renal veins and arteries after contrast medium administration. Multiple timed sets of coronal fast spoiled gradient-echo 70 degrees flip-angle images were acquired before and after contrast medium administration to derive MR renograms from changes in the signal intensity of the cortex and medulla. Precontrast T2-weighted images were obtained with a three-dimensional fast spoiled gradient-echo maximum intensity projection pulse sequence, and postcontrast T1 maximum intensity projection images were also obtained to depict the renal anatomy. RESULTS: Split filtration fraction differentiated normal from hydronephrotic kidneys. MR renograms depicted vascular, tubular, and ductal phases and differentiated between normal and hydronephrotic kidneys (P < .05, n = 20). Contrast medium dose correlated with the peak of the cortical signal intensity curves on the renogram (r = 0.7, P < .0005; n = 20). The sensitivities for the visual determination of hydronephrosis and unilateral delayed excretion of contrast material were both 100%, and the specificities were 64% and 85%, respectively. CONCLUSION: The preliminary findings show promise for the use of MR urography in the comprehensive assessment of renal function, dynamics, and anatomy.

Adult↗
PubMed2001

Tic convulsif caused by cerebellopontine angle schwannoma.

A case is presented of painful tic convulsif caused by schwannoma in the cerebellopontine angle (CPA), with right trigeminal neuralgia and ipsilateral hemifacial spasm. Magnetic resonance images showed a 4 cm round mass displacing the 4th ventricle and distorting the brain stem in the right CPA. The schwannoma, which compressed the fifth and seventh cranial nerves directly, was subtotally removed by a suboccipital craniectomy. Postoperatively, the patient had a complete relief from the hemifacial spasm and marked improvement from trigeminal neuralgia. The painful tic convulsif in this case was probably produced by the tumor compressing and displacing the anterior cerebellar artery directly.

Cerebellar Neoplasms↗
PubMed2001

Clinical usefulness of magnetic resonance cisternography in patients having hemifacial spasm.

To evaluate the usefulness of MR cisternography fourteen patients that had hemifacial spasm and 20 control patients underwent MR cisternography. All the patients with hemifacial spasm had a confirmed vascular compression after surgery. MR cisternography was performed using a 1.5-tesla superconducting MR magnet in which a 3D (dimensional) heavily T2-weighted turbo spin-echo sequence was used. In 34 randomly selected individuals, we retrospectively determined whether MR cisternography images could be used to evaluate symptoms, and what the benefits of obtaining this image was. The results were correlated with the surgical findings. The sensitivity was 100% and the specificity was 94% in all patients having a hemifacial spasm. The offending vessels were the anterior inferior cerebellar artery (AICA) in six patients cases, the posterior inferior cerebellar artery (PICA) in six, both the vertebral artery and PICA in one, and the vertebral artery in one. All the images showed good resolution and contrast, and also showed the exact correlation between the facial nerve and intracranial vessels in the multiplaner image. The findings of neurovascular compression were well correlated with the surgical findings. We believe that high-resolution 3D MR cisternography is a very useful method for evaluating the neurovascular compression in patients that have hemifacial spasm.

Adult↗
PubMed2000

A biodegradable polymer scaffold for delivery of osteotropic factors.

Despite discoveries and developments in osteotropic factors, therapies exploiting these macromolecules have been limited due to a lack of suitable delivery vehicles and three dimensional (3D) scaffolds that promote bone regeneration. To address this limitation, an emulsion freeze-drying process was developed to fabricate biodegradable scaffolds with controlled microarchitecture, and the ability to incorporate and deliver bioactive macromolecules for bone regeneration. The effect of median pore size and protein loading on protein release kinetics was investigated using scaffolds with different protein loading and median pore sizes ranging from 7 to 70 microm. Graphs of protein release from scaffolds showed an initial burst followed by a slower sustained release. Release kinetics were characterized using an unsteady-state, diffusion-controlled model with an effective diffusivity that took tortuosity (tau) and partition coefficient for protein adsorption (Kp) onto the scaffold walls into account. Tortuosity and partition coefficient significantly reduced the protein diffusivity by a factor of 41 +/- 43 and 105 +/- 51 for 60 and 30-microm median pore-sized scaffolds, respectively. The activity of the protein released from these scaffolds was demonstrated by delivering rhBMP 2 and [A-4] (an amelogenin derived polypeptide) proteins from the scaffold and regenerating bone in a rat ectopic bone induction assay [Whang et al. J Biomed Mater Res 1998;42:491-9, Veis et al. J Bone Mineral Res, Submitted].

Biocompatible Materials↗
PubMed1999

Engineering bone regeneration with bioabsorbable scaffolds with novel microarchitecture.

Critical-sized defects (CSDs) were introduced into rat calvaria to test the hypothesis that absorption of surrounding blood, marrow, and fluid from the osseous wound into a bioabsorbable polymer matrix with unique microarchitecture can induce bone formation via hematoma stabilization. Scaffolds with 90% porosity, specific surface areas of approximately 10 m2/g, and median pore sizes of 16 and 32 microm, respectively, were fabricated using an emulsion freeze-drying process. Contact radiography and radiomorphometry revealed the size of the initial defects (50 mm2) were reduced to 27 +/- 11 mm2 and 34 +/- 17 mm2 for CSDs treated with poly(D,L-lactide-co-glycolide). Histology and histomorphometry revealed scaffolds filled with significantly more de novo bone than negative controls (p < 0. 007), more osteoid than both the negative and autograft controls (p < 0.002), and small masses of mineralized tissue (< 15 mm in diameter) observed within the scaffolds. Based on these findings, we propose a change in the current paradigm regarding the microarchitecture of scaffolds for in vivo bone regeneration to include mechanisms based on hematoma stabilization.

Absorbable Implants↗
PubMed1998

Ectopic bone formation via rhBMP-2 delivery from porous bioabsorbable polymer scaffolds.

Drug delivery devices have received considerable interest in the field of tissue engineering due to the advent of proteins that can induce proliferation and differentiation of various cells to form specific tissues and organs, for example, bone morphogenetic protein (BMP-2) for osteogenesis. In this work the delivery of a clinically relevant bioactive factor, recombinant human rhBMP-2, was tested in vivo in a rat ectopic bone induction assay. Contact radiography and radiomorphometry showed significantly more radiopacity (1798+/-183 mm2 versus. 784+/-570 mm2 radiopaque area/g scaffold) in the BMP scaffolds than controls (p < 0.002). De novo woven bone and abundant osteoid formation were confirmed from histological sections while controls contained minimal amounts of tissue. Histomorphometry revealed significantly more bone (124+/-93 mm2 versus 7+/-12 mm2) and osteoid (72+/-43 mm2 versus 20+/-21 mm2) in the BMP implants (p < 0.001). These scaffolds demonstrated the ability to deliver viable rhBMP-2 and to induce bone formation in an ectopic site.

Absorption↗
PubMed1998

Vibrotactile stimulus order effects in somatosensory cortical areas of rhesus monkeys.

This study demonstrated effects of stimulus order on single-cell responses in the macaque primary and secondary somatosensory and 7b cortical areas. As part of a study of tactile attention, two monkeys (Macaca mulatta) received similar constant amplitude, sinusoidal tactile vibration patterns (125 Hz) at two glabrous skin, hand locations. The stimuli started asynchronously with offsets of 150 or 300 ms. In cells with bilateral receptive fields and increased firing to a stimulus, we observed an average lowering of 30% in the firing rates to the contralateral stimulus when preceded by stimulation of the ipsilateral hand. Some cells with only contralateral receptive fields showed similar depressed responses to a contralateral stimulus when preceded by an ipsilateral stimulus. Stimulus order effects were more prominent during dual stimulation of the receptive field on one hand. In six cells whose background activity was inhibited by the first stimulus, higher rates appeared at the onset of the second stimulus. These results suggest a possible substrate for psychophysical findings of stimulus masking in which a preceding stimulus depresses detection thresholds. The spatial and temporal characteristics of in-field inhibitory mechanisms best account for the observed stimulus order effects.

Animals↗
PubMed1998

The effects of serial stretch loading on stretch work and stretch-shorten cycle performance in the knee musculature.

Training methods to optimize stretch-shorten cycle performance and an active muscle's ability to resist a sudden stretch (stretch work) and the relationship between the two have not been fully explored. The purpose of this study was to examine the effects of an 8-week strengthening program of serial stretch loading on stretch work and stretch-shorten cycle performance in the quadriceps and hamstring muscles. Thirty-one asymptomatic subjects participated in pre- and post-tests of maximum voluntary isometric contractions, stretch work and stretch-shorten cycle trials, and single-leg vertical jumps. The training portion consisted of progressively resisted isotonic single-leg squats. One leg exercised against an isotonic load with serial stretch loading, while the other leg exercised against isotonic load alone. Training resulted in strength gains in both legs indicated by the increase in weight lifted during training, but not by maximum voluntary isometric contractions. Vertical jump height increased in both legs. In the hamstring, stretch work decreased and stretch-shorten cycle performance increased in both legs. In the quadriceps, serial stretch loading intervention resulted in increased stretch-shorten cycle performance and no significant change in stretch work. The correlation between stretch-shorten cycle and stretch work was weak but significant. These findings suggest that the use of serial stretch loading could improve muscular performance and enhance a muscle's potential for dynamic stabilization.

Adult↗
PubMed1997

Human keratinocytes maintain reversible anti-apoptotic defenses in vivo and in vitro.

Human keratinocytes proliferate and differentiate in an epidermal environment where induction of apoptosis can be triggered by ultraviolet radiation (UVR), activated lymphocytes and cytokines. The purpose of this study was to determine whether keratinocytes were susceptible to apoptosis induced by ionophore, ultra-violet radiation, cytokines or crosslinking of CD95 (Fas/APO-1). In normal human skin exposed to two minimal erythema doses of ultraviolet radiation, suprabasal cells were the first keratinocytes to demonstrate apoptotic nuclei, and by 48 h apoptotic cells were identified throughout the mid to upper epidermis. However, most keratinocytes resisted apoptosis and UVR-induced apoptosis was not observed in basal cells, or in the most differentiated epidermis. Human keratinocytes and keratinocyte cell lines cultured in vitro developed maximal apoptosis 48 h after radiation. Human keratinocytes cultured in full growth factor supplements were resistant to UVR-induced apoptosis compared to keratinocyte cell lines or to a lymphoid cell line (HL60) susceptible to apoptosis. Keratinocyte cell lines were completely resistant to apoptosis induced by interferon-gamma, interferon-alpha, IL-2, IL-6, TNF-alpha, IL-1Ra, and GM-CSF. A subset of the cells in cultures of keratinocytes and transformed keratinocyte cell lines died by apoptosis in response to anti-Fas, IL-1alpha and TNF-alpha plus IFN-gamma and ionophore. Second passage freshly isolated human keratinocytes were much more resistant to apoptosis induced by ionophore, anti-Fas and cytokines than were transformed keratinocyte cell lines. Calcium shift to induce differentiation in second-passage keratinocyte cultures made keratinocytes even more resistant to UVR-induced apoptosis. This parallels the lack of UVR-induced apoptosis observed in the most differentiated keratinocytes in irradiated human skin. Both keratinocytes and keratinocyte cell lines express rather low levels of the anti-apoptotic proteins bcl-2 and bcl-x compared to other apoptosis-resistant cell types. The differences between keratinocytes and keratinocyte cell lines in susceptibility to apoptosis are not explained by difference in expression of bcl-2 or bcl-x. Finally, withdrawal of growth factors from keratinocytes decreased cell survival following UVR and increased the induction of apoptosis. Inhibition of protein synthesis with cyclo-heximide also made keratinocytes more susceptible to UVR-induced apoptosis, indicating that anti-apoptotic defences in cultured keratinocytes are dependent on active protein synthesis. These experiments show that the strong keratinocyte defences against apoptosis are stratified within the epidermis, and can be altered by differentiation and growth factor withdrawal.

Journal Article↗
PubMed1988

Oligotrophic bacteria from rendzina forest soil.

Oligotrophic bacteria were shown to exist abundantly in all layers of a rendzina forest soil throughout the year. Two-hundred-three oligotrophic bacteria were isolated from forest soil (Aoba, Sendai) at different layers (L, F, H and A layers) throughout the year, and their morphological and physiological characteristics were examined. A high proportion (95%) of the isolated oligotrophs were Gram-negative, non-spore forming bacteria. Based on the cell shape, the isolates were divided into four groups: regular rods, curved/spiral bacteria, irregular rods, and buddin and/or prosthecate bacteria. Each group of bacteria is discussed in relation to the physiological characteristics. Notably oligotrophic bacteria of different cell types showed a marked zonal distribution in respect to profile depth.

Bacteria↗
PubMedDate not supplied

Giant serpentine intracranial aneurysm: a case report.

The authors present a case of giant serpentine aneurysm (a partially thrombosed aneurysm containing tortuous vascular channels with a separate entrance and outflow pathway). Giant serpentine aneurysms form a subgroup of giant intracranial aneurysms, distinct from saccular and fusiform varieties, and in this case, too, the clinical presentation and radiographic features of CT, MR imaging and angiography were distinct.

Cerebral Angiography↗