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Biomedical subjects

C K Cheng

Publications and source records attributed to C K Cheng.

At least 19 recordsLinked to original sources
PubMed1995

Contact areas and pressure distributions in the subtalar joint.

We investigated how foot position and ankle arthrodesis affect the contact characteristics of the subtalar joint. Nine fresh-frozen specimens of amputated lower legs were used. Pressure-sensitive films were inserted into the anterior and posterior articulation of the subtalar joint. The contact areas and pressure for various foot positions and under axial loads of 600, 1200, and 1800 N were determined based on the gray level of the digitized film. In neutral position and under a 600 N load, the maximum contact pressure in the subtalar joint was 5.13 +/- 1.16 MPa. The contact area (1.18 +/- 0.35 cm2) was only 12.7% of the whole subtalar articulation area (9.31 +/- 0.66 cm2), and the total force (348.5 +/- 41.7 N) transmitted via this contact area was about 58% of the applied load (600 N). Dorsiflexion of the foot increased the contact area and the force transmitted, but decreased the average contact pressure in the subtalar joint, while the reverse occurred in plantar flexion. Eversion increased the subtalar contact stress, whereas inversion up to 10 degrees decreased it. Ankle joint arthrodesis shifted the contact areas in the subtalar joint posteriorly in all inversion/eversion positions. Moreover, total force transmitted through the subtalar joint as well as the contact pressure increased.

Adult↗
PubMed1995

A cellular automata model of the hydrophobic effect.

Dynamic simulations of solute molecules in water are made using cellular automata. By varying the parameter governing the breaking probability of water-solute tesselated pairs, sets of configurations were modeled of solutions ranging from polar to non-polar solutes. The emergent behavior of the non-polar solute models leads us to believe that this is a possible model of the hydrophobic effect.

Models, Chemical↗
PubMed1995

Acyclovir treatment for linear endotheliitis on grafted corneas.

Two patients with previous corneal transplants developed unusual rejection-like episodes of the grafted cornea. Both had a migrating line of keratic precipitates and stromal edema involving both the donor and recipient corneas. Intensive steroid treatment attained little effect, but oral acyclovir treatment dramatically suppressed the disease process. The facts suggest that a virus-related immune mechanism against both the donor and recipient endothelia, rather than simple allograft rejection, may have been responsible for the clinical presentations. Oral acyclovir therapy might be considered in patients with steroid-nonresponsive corneal endotheliitis mimicking allograft rejection.

Acyclovir↗
PubMed1995

The application of cepstral coefficients and maximum likelihood method in EMG pattern recognition.

A new technique for classifying patterns of movement via electromyographic (EMG) signals is presented. Two methods (conventional autoregressive (AR) coefficients and cepstral coefficients) for extracting features from EMG signals and three classification algorithms (Euclidean Distance Measure (EDM), Weighted Distance Measure (WDM), and Maximum Likelihood Method (MLM)) for discriminating signals representative of broad classes of movements are described and compared. These three classifiers are derived from Bayes classifier with some assumptions, the relationship among them is discussed. The conventional MLM is modified to avoid heavy matrix inversion. Six able-bodied subjects with two pairs of surface electrodes located on bilateral sternocleidomastoid and upper trapezius muscles were studied in the experiment. The EMG signals of 20 repetitions of 10 motions were analyzed for each subject. Experimental results showed that mean recognition rate of the cepstral coefficients was at least 5% superior to that of the AR coefficients. The improvement achieved by the cepstral method was statistically significant for all the three classifiers. Reasons for the superiority of cepstral features were investigated from the feature space and frequency domain, respectively. The cepstral coefficients owned better cluster separability in feature space and they emphasized the more informative part in the frequency domain. The discrimination rate of the MLM was the highest among three classifiers. Incorporation of the cepstral features with the MLM could reduce the misclassification rate by 10.6% when compared with the combination of AR coefficients and EDM. Proper choice of five of ten motions could further raise the recognition rate to more than 95%.

Adult↗
PubMed1995

The center of ground reaction force during lifting.

The center locations of the ground reaction force were estimated when subjects assumed upright and bending postures as well as when they lifted at low and high speeds. Ten subjects participated in this study and were instructed to assume two postures and to perform two liftings sequentially in a random order. The center locations of the ground reaction force were calculated using a Computerized Dyno Graphic system (INFOTRONIC). The center of the ground reaction force in the full bending posture had a more anterior location than it did in the upright standing posture. When measured during the lifting activity, the center of the ground reaction force shifted forward and then backward during the whole activity. The center location shifted to a more anterior location during high-speed lifting than it did during low-speed lifting.

Adult↗
PubMed1995

Intravitreal sustained-release dexamethasone device in the treatment of experimental uveitis.

PURPOSE: Uveitis often runs a chronic course requiring long-term therapy. Topical treatment results in poor intravitreal penetration, and systemic therapy is associated with significant side effects. The authors investigated whether an intravitreal sustained-release dexamethasone device was effective in the treatment of severe panuveitis in a rabbit model. METHODS: Twenty New Zealand white rabbits were immunized twice subcutaneously with 10 mg of Mycobacterium tuberculosis H37Ra antigen. Twelve days later, sustained-release dexamethasone devices were implanted into the vitreous of the right eye of 10 rabbits. Ten control rabbits received a sham device. One day later, rabbits were challenged with an intravitreal injection of 33 micrograms of antigen. Three animals in each group were sacrificed on post-challenge days 7 and 13 for aqueous white blood cell (WBC) count, protein determination, and histologic examination. To simulate chronic inflammation with exacerbations, the eight remaining eyes were rechallenged with intravitreal antigen on day 15 and were observed for 3 1/2 months. Inflammation was graded clinically by two masked observers. Retinal function was evaluated by electroretinography (ERG). Light microscopy was used to evaluate the eyes histopathologically. The amount of residual drug in the devices was measured on day 13 and at the end of the experiment. RESULTS: By all clinical criteria measured--anterior chamber cells, flare, and vitreous opacity--treated eyes had significantly less inflammation than untreated eyes (P < 0.05). Clinical examination correlated well with objective data. Both protein concentration (P < 0.05) and aqueous WBCs (P < 0.02) were approximately 10-fold higher, and ERGs were significantly depressed (P < 0.05) in untreated eyes compared to treated eyes. Histopathologic examination showed marked inflammation and tissue disorganization in the untreated compared to the treated eyes. After antigen rechallenge, inflammation in experimental eyes was still less than in control eyes. Late complications such as corneal neovascularization, cataract, and hypotony were also less in the treated eyes than in the untreated eyes. At the end of the experiment (99 days after device implantation), approximately 30% of drug remained in the devices. CONCLUSIONS: The intravitreal sustained-release dexamethasone device is highly effective in suppressing inflammation and preventing complications after two episodes of experimental uveitis in a rabbit model for at least 3 1/2 months. This device may be useful in the management of patients with severe chronic posterior uveitis who cannot tolerate systemic or periocular therapy.

Animals↗
PubMed1994

Biomechanical analysis in ladder climbing: the effect of slant angle and climbing speed.

This paper presents the findings of a study conducted to determine the peak forces generated in the articulated joints and the foot/floor contact point of a ladder while an individual was engaged in ladder climbing. A kinematic description of joint movements and the calculation of forces acting on each body segment as well as the foot of the ladder were obtained on the basis of videographic data. Task variations were (1) slant angle (70 degrees and 75 degrees with the horizontal) and (2) climbing speed (86 steps/min and 106 steps/min). It was identified in this study that the ladder's friction forces had a time variant nature as a result of biodynamic movements. There were two peak friction coefficients, in opposite directions, occurring at 7% and 38% of each half of the strike time. The primary differences between climbing the ladders at 70 and 75 degrees were a greater posterior displacement of the body's center gravity and smaller peak center gravity shearing forces in climbing the 75 degree ladder. There were greater posterior displacement of the center gravity of body and a larger biomechanical load while climbing at 106 steps/min than at 86 steps/min.

Adult↗
PubMed1994

The use of surface EMG in knee extensor moment prediction.

A systematic method of EMG quantification is developed to estimate the isometric muscle moment directly from quantified surface EMG. This method includes the EMG Signals acquired from an acupuncture point Fu-Tu located on the quadriceps muscle group, an EMG smoothing scheme, an electromechanical time lag estimation, and a mathematical model with the polynomial regression function to quantify the EMG. Three subjects were asked to be tested on the CYBEX II dynamometer with a knee joint angle of 90 degree flexion and hip joint angle of also 90 degrees. They were asked to perform "two" trials of maximal voluntary contraction and "three" trials of free voluntary contraction of the isometric exercise. The first two trials were used to build up the quantification model, and the latter three trials served as data for the validation of the method. A Medelec MS92 EMG system with surface EMG electrodes was used to acquire the EMG Signals. In the determination of the regression order of the polynomial equations, the threshold value 0.0001 of the difference of the coefficient of determination values was used. The results of the polynomial regression orders are all 6 for three subjects, which reflects a tendency of nonlinear behavior of the EMG/moment relationship. A validation scheme was proposed to calculate the root mean square difference (RMSD) of the measured knee extensor moments from the CYBEX II dynamometer and estimated moments from the EMG quantification. The mean values of the RMSD of the three subjects were 0.0597, 0.0679 and 0.1080. These results demonstrate that the present approach can estimate the isometric muscle moment exerted by the quadriceps muscle group.

Acupuncture Points↗
PubMed1991

Gait analysis after total knee replacement for degenerative arthritis.

Using quantitative gait analysis and clinical evaluation, the functional results of 18 total knee replacement (TKR) in 13 patients who had osteoarthritis were evaluated. Nine knees each were replaced by Insall-Burnstein (I/B) posterior stabilized design or Miller-Galante (M/G) prosthesis. The former was fixed by cement and needed to sacrifice posterior cruciate ligament (PCL), while the latter was inserted without cement, and PCL could be reserved. The follow-up period ranged from 21 to 77 months. At the final follow-up, the overall functional knee score was 94.1 points (I/B 95.0 versus M/G 92.2). The average active knee flexion was 109.7 degrees (I/B 116.4 degrees versus M/G 102.9). For gait analysis, three cameras synchronized with 2 AMTI force plates were connected to the VICON system to provide kinetic and kinematic data during level walking. The data were compared with the non-operated side; and with younger subjects as normal control. They were supposed to possess normal knee functions. In patients after knee prosthesis, they tended to have slower velocity, shorter step length and less cadence. They also showed shorter swing and longer stance phases. In the M/G knee ground, the duration for double-limb support was longer, but shorter for single-limb support. The angles of knee flexion-extension of both prosthetic groups became narrower. Their ground reaction forces in both vertical and medio-lateral directions were larger than in the control groups, probably due to quadriceps dysfunction and subtle imbalance of the soft tissue-prosthesis complex around the joint.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Biomechanical studies of the anterior spinal fixators after corpectomy in pigs.

An unstable corpectomy porcine spinal model was created for the testing of anterior spinal fixators including: Kaneda device (KD), combination of Polster-Brinckmann prosthesis and Zielke implant (PBZ), and a new prototype device (CH). These spinal implants were examined in a one above/one below corpectomy model to determine the relative stiffness of each construct and the deformation of the adjacent discs under loading. The results indicated that the relative torsion and flexion stiffness were higher for the tested spines fixed with KD and CH. However, the relative compression stiffness of the tested spines was the same for all devices. The rigidity of the spinal constructs, which were measured around the corpectomy region showed the same tendency as above. However, the stiffness of CH and KD constructs were significantly higher than that of the PBZ construct under flexion and torsion. The difference in deformation of the upper and lower adjacent discs was not obvious among the intact spine and the spinal constructs with different devices. Clinical relevances: The corpectomy model represents a "worst case" scenario of spinal instability. In many conditions, spinal reconstructive surgery can restore axial compressive, torsional, and flexural rigidity to normal levels. These experimental conclusions apply to acute restoration of stability, rather than to rigidity after long-term cyclical loading. These three anterior fixators extended to only one cephalad level and one caudal level beyond the corpectomy defect. The new prototype device (CH) has a stability to the Kaneda device. The superior mechanical strength and simpler operative procedure of the new device provide for a potential clinical advantage in restoration of unstable spinal conditions.

Animals↗
PubMed1991

Choroideremia: a study of two families.

Choroideremia is a bilateral and progressive chorioretinal degenerative disease of X-linked inheritance. In Taiwan, the disease has rarely been reported. We recently found 8 male patients and 5 female carriers in two Chinese families with choroideremia and studied the clinical, psychophysical and electrophysiological properties of the disease. All patients revealed characteristic fundus and fluorescein angiographic changes in retinal pigment epithelium, and choroidal atrophy of variable extent. The severity of the functional impairments paralleled the fundus changes and the patients' age. However dark adaptation and the visual field were affected earlier than visual acuity and color sensation. In addition, rod cell impairment was found to be more severe than cone cell impairment in the electroretinographic studies. On the other hand, all carriers revealed similar diffuse punctate pigmentary changes and only mild abnormalities in dark adaptation. These findings may suggest that in choroideremia patients the photoreceptor cells are very sensitive to the influence of the choroidal atrophy, and that rod cells may be even more vulnerable than cone cells.

Adult↗
PubMed1990

Spinal stresses in simulated raking with various rake handles.

Five young male subjects performed a simulated raking task by pushing and pulling 14 different rake handles at 60 N and 110 N simulated soil resistance in a random order. The raking action was performed at a self-selected uniform pace over a 60 cm stroke length with initial, middle and final phases marked. During this action the raking force and angle of the rake was measured by a load cell and a potentiometer respectively. The posture was recorded with a video cassette recorder. The posture and force values were used for the determination of the spinal compression load. In rake pulling the 13 modified rake handles generated a spinal compression of only 20% to 50% of the straight handle, whereas in rake pushing the modified handles generated compression up to five times that of the straight handle. The compression generated with the straight handle never reached the action limit, whereas those of the 13 modified handles rarely stayed within the action limit. Therefore, a straight handle is considered the handle of choice.

Adult↗
PubMed1990

The joint distribution problem with multiple articular contact forces.

The single joint distribution problem with two or more unknown bony contact forces is considered, and an optimal solution procedure free of ad hoc assumptions is described. If two bony contact forces are present, a strictly muscle force dependent equality constraint exists that allows for initial independent estimation of muscle forces, followed by unique estimation of all bony contact force components perpendicular to the straight line connecting their known points of application. However, if three or more bony contact forces are present, no strictly muscle force dependent equality constraint exists, solution separability is lost, and optimal muscle and bony contact forces are obtained simultaneously.

Biomechanical Phenomena↗
PubMed1988

Transcriptional control of high molecular weight keratin gene expression in multistage mouse skin carcinogenesis.

Monospecific antikeratin antisera and specific complementary DNA probes were used to analyze expression of keratin genes in newborn mouse skin and skin papillomas and carcinomas by indirect immunofluorescence, immunoblotting, and in situ hybridization. Tumors were induced by initiation with 7,12-dimethylbenz[a]anthracene and promotion with 12-O-tetradecanoylphorbol-13-acetate. Type I epidermal keratin K14 protein (Mr 55,000) is found in all living layers of the newborn skin but is most abundant in the lower strata. K1 (Mr 67,000) and K10 (Mr 59,000) proteins are predominantly suprabasal and K1 is processed in the stratum corneum. Transcripts for K14 were confined largely to the basal cell layer by in situ hybridization. Transcripts for K1 and K10 were highly expressed in suprabasal cells including the granular cell layer. In benign tumors, distribution of K14 protein is similar to that in newborn skin, while the abundance of K1 and K10 appears to be somewhat reduced although the tissue distribution remains suprabasal. Transcription of K14 is aberrant in benign tumors and transcripts persist throughout much of the suprabasal cell layers. Transcripts of K1 and K10 are normally distributed in papillomas but grain density is less intense than in newborn epidermis. Keratin expression in carcinomas is highly disturbed. K14 protein and transcripts are highly expressed in all strata in carcinomas while protein and transcripts for K1 and K10 are essentially absent. These results suggest that papilloma cells fail to respond to or generate signals to regulate K14 expression in the differentiating suprabasal cell layers and may not fully express their suprabasal cell keratins. Carcinomas fail to express suprabasal cell keratins and this is regulated at the transcriptional level. The loss of suprabasal keratin expression may provide a marker for malignant conversion in the mouse skin carcinogenesis model.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1988

Molecular cloning of mouse epidermal cystatin A and detection of regulated expression in differentiation and tumorigenesis.

A gamma gt 11 cDNA expression library representing mouse epidermis mRNA was screened with polyclonal rabbit antiserum directed against 10-13 kDa epidermal antigens that had previously been shown to be regulated during epidermal differentiation. A cDNA clone was detected and isolated and its identity as the coding sequence for one of the antigens was confirmed by translation of hybrid-selected mRNA from mouse epidermis. The cDNA sequence predicted a peptide homologous to the reported sequence of rat epidermis cystatin A, a thiol proteinase inhibitor. This identification was confirmed by cross-reactivity of the gamma clone fusion protein with authentic antiserum to rat epidermis cystatin A. Southern gel analysis showed that mouse DNA may contain several closely related genes homologous to the cystatin probe. An mRNA of about 0.6 kb from epidermis and cultured mouse epidermal cells hybridized with the cystatin probe on northern analysis. The abundance of the message was high in cultured basal cells and was selectively diminished by inducing terminal differentiation in culture with an elevated Ca2+ concentration in the medium. Cystatin message was abundant in chemically induced mouse skin papillomas but reduced in carcinomas. In epidermis, mRNA was localized to the less differentiated basal and lower spinous layers by in situ hybridization. Regulation of expression of cystatin A in epidermis and tumors suggests that it may be important in the control of normal keratinocyte proliferation and differentiation and in malignant conversion.

Amino Acid Sequence↗
PubMed1986

An extrachromosomal plasmid is the etiological precursor of kalDNA insertion sequences in the mitochondrial chromosome of senescent neurospora.

In the kalilo strains of N. intermedia, senescence is initiated by insertion of a 9.0 kb foreign nucleotide sequence, kalDNA, into mitochondrial DNA. A 9.0 kb linear DNA plasmid that is structurally homologous to the mitochondrial kalDNA insertion sequences exists in high copy numbers in close association with the nuclei of presenescent and senescent kalilo cells, but is not present in cells of long-lived normal strains. The free kalilo plasmid has not been detected in mitochondria, suggesting that the element does not contain a mitochondrial origin of replication. Unexpectedly, the nuclear plasmid, like the mitochondrial insertion element, follows a strict pattern of maternal inheritance. We surmise that the extramitochondrial plasmid is the etiological precursor of the kalDNA insertion sequences that appear in the mtDNAs of senescent cell lines and conclude that the kalilo element induces senescence because it is a mutator of mitochondrial genes.

DNA Replication↗