Search PubMed⌕ Search

Biomedical subjects

J W Chow

Publications and source records attributed to J W Chow.

At least 37 records · Page 2Linked to original sources
PubMed1999

Knee joint forces during isokinetic knee extensions: a case study.

OBJECTIVE: To describe the procedures to obtain knee joint forces during isokinetic knee extensions and evaluate the patellar ligament force, quadriceps tendon force, patellofemoral and tibiofemoral joint forces at different speeds measured from a female subject. DESIGN: A technical note with a case study. BACKGROUND: Two previous studies examined knee joint forces during isokinetic knee extension using different techniques reported inconsistent findings. Also, the highest speed used in these two studies (180 degrees s(-1)) were much lower than the maximum speeds available in modern isokinetic dynamometers. METHODS: The subject performed maximum effort isokinetic knee extensions at 16 different speeds ranged from 25 to 400 degrees s(-1). The gravitational and inertial effects were included in determining the resultant knee torque. Knee radiographs were used to determine the knee joint geometry. A combination of knee torque and geometric data was used to determine different knee joint forces. RESULTS: All knee joint forces were found to decrease with increasing isokinetic speed. The tibiofemoral shears forces indicated that the anterior cruciate ligament was loaded throughout the range of motion. CONCLUSIONS: The magnitudes of knee joint forces are largely depending on the knee torque values. RELEVANCE: Isokinetic knee extensions are considered appropriate for the early part of the rehabilitation for patients with knee dysfunctions due to the lesser demand of coordination. However, to reduce the knee joint forces, submaximal efforts at lower speeds or maximal efforts at higher speeds are recommended.

Adult↗
PubMed1999

Combination antibiotic therapy versus monotherapy for gram-negative bacteraemia: a commentary.

Whether combination antimicrobial therapy is more efficacious than monotherapy for gram-negative bacteraemia remains controversial. Although there are theoretical advantages to combination therapy that are buttressed by in vitro and animal studies, the data from studies of patients with gram-negative bacteraemias have been conflicting. A review of selected clinical studies suggests that combination therapy is associated with improved outcome typically only in severely ill patients and its efficacy may be further limited to those with Pseudomonas aeruginosa, Klebsiella spp. or Enterobacter spp. bacteraemia.

Anti-Bacterial Agents↗
PubMed1999

The role of prostaglandins and nitric oxide in the response of bone to mechanical forces.

We have developed an experimental model whereby bone is exposed to a brief episode of mechanical stimulation, which is followed by bone formation. The earliest response is in osteocytes, which express c-fos and insulin-like growth factor (IGF-1) within 30-60min. Thirty-six to 72h after loading bone matrix gene expression occurs on bone surfaces. The osteogenic response can be suppressed by a single dose of nitric oxide synthase (NOS) or prostaglandin (PG) synthase inhibitors, if these are administered just before mechanical stimulation: similar doses after stimulation have no effect. There is a later phase of indomethacin-sensitivity associated with COX-2 expression in bone at 6h. Thus, mechanically induced osteogenesis involves early expression of c-fos and IGF-1 by osteocytes, which are believed to be the strain-sensitive cells in bone. Both NOS and PG synthase, either in parallel or in sequence, are crucial to the initial transduction of the mechanical stimulus into an osteogenic response.

Animals↗
PubMed1999

Muscle activation during the tennis volley.

PURPOSE: To broaden our understanding of muscle function during the tennis volley under different ball placement and speed conditions by examining the activity of selected superficial muscles of the stroking arm and shoulder (flexor carpi radialis, extensor carpi radialis, triceps brachii, deltoids, and pectoralis major) and muscles related to postural support (left and right external oblique, lumbar erector spinae, and gastrocnemius) during the volley. METHODS: Seven skilled tennis players were asked to perform volley strokes under 18 experimental conditions, including variations in lateral contact location (forehand and backhand), ball contact height (high, middle, and low), and ball speed (fast, medium, and slow). A ball machine was modified so that the subjects could not predict the ball trajectory before it was released from the machine. Muscle activity was determined using surface electromyographic (EMG) techniques, and the critical instants of a volley were determined using two force platforms and two high-speed (120 Hz) video cameras. Average EMG values for different phases of the volley, defined by the critical instants, were computed. RESULTS AND CONCLUSIONS: In general, muscle activity increased with increasing ball speed. The extensor carpi radialis was more active than the flexor carpi radialis during both forehand and backhand volleys, suggesting the importance of wrist extension/abduction and grip strength. The increase in EMG levels in the forearm muscles shortly before the ball impact indicated that the subjects did not tighten their grip and wrist until moments before ball impact. Both antero-middle and postero-middle deltoids were active in most stroke phases. However, the roles of the deltoid muscles during a volley cannot be determined without knowing the actions of the other shoulder joint muscles.

Adolescent↗
PubMed1999

Movement characteristics of the tennis volley.

PURPOSE: The purpose of this study was to examine selected movement characteristics of the tennis volley by evaluating temporal and ground reaction force (GRF) parameters. METHODS: Seven skilled tennis players performed volley strokes under 18 experimental conditions including variations in lateral contact location (forehand (FH) and backhand (BH)), ball contact height (high, middle, low), and ball speed (fast, medium, slow). A ball machine was modified so that the subjects could not predict the ball trajectory before it was released from the machine. The GRF and temporal parameters were determined using two force platforms and two high-speed (120 Hz) video cameras, respectively. Average and maximum values of each measured parameter were computed for different phases of the volley. RESULTS: The average reaction times (from ball release to initial racquet movement (IRM)) for FH and BH trials were 226 and 205 ms, respectively, and the difference was statistically significant. The average stroke time (from IRM to ball impact) ranged from 381 ms in fast speed trials to 803 ms in slow speed trials. A distinct racquet forward motion immediately before ball impact occurred in 75% of the trials and they were evenly distributed between FH and BH trials. An ipsilateral side step (a side step of the foot on the same side of the oncoming ball before the crossover step of the other foot) occurred more often in FH (45%) than in BH (34%) trials. CONCLUSIONS: The GRF during the stroke phase suggest that the subjects initiated lateral movement by leaning sideward when ball velocity was low and by a vigorous pushoff of the contralateral foot when ball velocity was high.

Adolescent↗
PubMed1999

Discus throwing performances and medical classification of wheelchair athletes.

PURPOSE: The purpose of this study was to identify those kinematic characteristics that are most closely related to the medical classification and measured distance of a throw. METHODS: Two S-VHS camcorders (60 fields x s(-1) were used to record the performance of 14 males of different classes. Each subject performed 10 trials and the best two trials from each subject were selected for analysis. Three-dimensional kinematics of the discus and upper body segments at the instant of release and the range of motion and average angular speed of different segments during the final forward swing were determined. RESULTS: The speeds of the discus at release, ranging from 9.9 to 17.2 m x s(-1), were smaller than those exhibited by elite male able-bodied throwers. However, the angles of release, ranging from 24.6 to 41.4 degrees, were comparable with those observed in able-bodied throwers. Of the segmental kinematic parameters, (a) the inclination and angular speed of the upper arm at release; (b) the ranges of motion of the shoulder girdle, upper arm, and forearm during the forward swing; and (c) the average angular speed of the shoulder girdle during the forward swing were significantly correlated to both the classification and measured distance. The inclinations of different segments at the instant of release suggested that athletes with high level of spinal cord injury emphasized the elbow flexion to compensate for the deficiency in shoulder girdle movement. CONCLUSIONS: In addition to the speed of the discus at release, the shoulder girdle movement during the forward swing is an important determinant of classification and measured distance.

Acceleration↗
PubMed1999

The maximum shortening velocity of muscle should be scaled with activation.

The purpose of this study was to determine whether the maximum shortening velocity (Vmax) in Hill's mechanical model (A. V. Hill. Proc. R. Soc. London Ser. B. 126: 136-195, 1938) should be scaled with activation, measured as a fraction of the maximum isometric force (Fmax). By using the quick-release method, force-velocity (F-V) relationships of the wrist flexors were gathered at five different activation levels (20-100% of maximum at intervals of 20%) from four subjects. The F-V data at different activation levels can be fitted remarkably well with Hill's characteristic equation. In general, the shortening velocity decreases with activation. With the assumption of nonlinear relationships between Hill constants and activation level, a scaled Vmax model was developed. When the F-V curves for submaximal activation were forced to converge at the Vmax obtained with maximum activation (constant Vmax model), there were drastic changes in the shape of the curves. The differences in Vmax values generated by the scaled and constant Vmax models were statistically significant. These results suggest that, when a Hill-type model is used in musculoskeletal modeling, the Vmax should be scaled with activation.

Adolescent↗
PubMed1999

A Web-based digitized video image system for the study of motor coordination.

A Web-based instructional project for the study of motor coordination is presented. The project includes two components: a tutorial on motor coordination and an interactive digitized video image system developed for the analysis of motion, including topics in biomechanics, motor coordination, motor control, and motor skill. This interactive system allows for the quantitative analysis of stored video images that are accessible from the World-Wide Web. The use of this digitizing system for the measurement and analysis of human locomotion coordination patterns is presented.

Computer-Assisted Instruction↗
PubMed1998

In vitro susceptibility and molecular analysis of gentamicin-resistant enterococci.

Enterococci with gentamicin MICs of 256 to 1,024 micrograms/mL were evaluated for susceptibility to ampicillin plus gentamicin synergism. Sixteen of eighteen enterococcal isolates were not susceptible to synergistic killing by ampicillin plus gentamicin; 11 possessed aac(6')-aph(2"), and 4 possessed aph(2")-Ic. A gentamicin MIC of 512 or 1,024 micrograms/mL predicted lack of ampicillin/gentamicin synergism, but a gentamicin MIC of 256 micrograms/mL did not. For six enterococcal strains possessing the gentamicin-resistance gene aph(2")-Ic, ampicillin plus dibekacin, ampicillin plus netilmicin, and ampicillin plus amikacin produced synergistic killing in five, three, and two strains, respectively.

Amikacin↗
PubMed1998

Nitric oxide synthase expression in bone cells.

We have localized the expression of the three main nitric oxide synthases (eNOS, bNOS, and iNOS) in bone cells of rats and humans using immunohistochemistry. The predominant isoform expressed in normal adult bone was the constitutive isoform, eNOS, mainly in cells of osteoblastic lineage. In adult bone, the osteoblast lineage cells exhibiting eNOS expression were flat bone lining cells and osteocytes, but cuboidal osteoblasts were consistently negative. Expression for bNOS was not detected in any bone cells. iNOS expression was not detected in any cells of osteoblastic lineage in normal adult rat or human bone, but was observed in cuboidal osteoblasts of adult rats with experimental colitis, in which the suppression in bone formation may be cytokine mediated. Osteoclasts in normal rat tissue showed expression for both eNOS and iNOS, but these were patchy. As for cells of the osteoblast lineage, osteoclasts were negative for bNOS. Thus, our findings support evidence, from in vitro studies and from animal experiments, that nitric oxide may play an important role in the physiology of bone.

Animals↗
PubMed1998

Antimicrobial resistance in enterococci isolated from Turkey flocks fed virginiamycin.

From 125 separate cloacal cultures from three turkey flocks fed virginiamycin, 104 Enterococcus faecium and 186 Enterococcus faecalis isolates were obtained. As the turkeys aged, there was a higher percentage of quinupristin-dalfopristin-resistant E. faecium isolates, with isolates from the oldest flock being 100% resistant. There were no vancomycin-resistant enterococci. Results of pulsed-field gel electrophoresis (PFGE) indicated there were 11 PFGE types of E. faecalis and 7 PFGE types of E. faecium that were in more than one group of flock cultures.

Animals↗
PubMed1998

A new high-level gentamicin resistance gene, aph(2'')-Id, in Enterococcus spp.

Enterococcus casseliflavus UC73 is a clinical blood isolate with high-level resistance to gentamicin. DNA preparations from UC73 failed to hybridize with intragenic probes for aac(6')-Ie-aph(2'')-Ia and aph(2'')-Ic. A 4-kb fragment from UC73 was cloned and found to confer resistance to gentamicin in Escherichia coli DH5alpha transformants. Nucleotide sequence analysis revealed the presence of a 906-bp open reading frame whose deduced amino acid sequence had a region with homology to the aminoglycoside-modifying enzyme APH(2'')-Ic and to the C-terminal domain of the bifunctional enzyme AAC(6')-APH(2''). The gene is designated aph(2'')-Id, and its observed phosphotransferase activity is designated APH(2'')-Id. A PCR-generated intragenic probe hybridized to the genomic DNA from 17 of 118 enterococcal clinical isolates (108 with high-level gentamicin resistance) from five hospitals. All 17 were vancomycin-resistant Enterococcus faecium isolates, and pulsed-field typing revealed three distinct clones. The combination of ampicillin plus either amikacin or neomycin exhibited synergistic killing against E. casseliflavus UC73. Screening and interpretation of high-level aminoglycoside resistance in enterococci may need to be modified to include detection of APH(2'')-Id.

Anti-Bacterial Agents↗
PubMed1998

Molecular analysis of glycopeptide-resistant Enterococcus faecium isolates collected from Michigan hospitals over a 6-year period.

The purpose of this study was to evaluate the molecular relatedness of clinical isolates of glycopeptide-resistant Enterococcus faecium isolates collected from hospitals in Michigan. A total of 379 isolates used in this study were all vancomycin-resistant E. faecium isolates collected from 28 hospitals and three extended-care facilities over a 6-year period from 1991 to 1996. For the 379 isolates, there were 73 pulsed-field gel electrophoresis (PFGE) strain types. Within strain types, there were as many as six restriction fragment differences. Most isolates (70%) belonged to six strain types, which were designated M1 (36%), M2 (3%), M3 (18%), M4 (6%), M10 (4%), and M11 (3%). PFGE strain M1 was cultured from 135 patients in 13 hospitals during the period 1993 to 1996. Strain type M2 was cultured from 11 patients in two hospitals during the period 1991 to 1992 and was not observed after 1992. Strain type M3 was cultured from 70 patients in 10 hospitals during the period of 1994 to 1996. Both M4 and M10 were cultured from 23 patients in three hospitals and from 15 patients in two hospitals, respectively, during 1995 to 1996. M11 was cultured from 13 patients in four hospitals during 1996. A total of 23 of 28 hospitals had evidence of clonal dissemination of some isolates. Plasmid content and hybridization analysis done on 103 isolates from one hospital and two affiliated extended-care facilities indicated that the strains contained from one to eight plasmids. Mating experiments indicated transfer of vancomycin resistance from 94 of these isolates into plasmid-free E. faecium GE-1 at transfer frequencies of <10(-9) to 10(-4). Gentamicin resistance and erythromycin resistance were cotransferred at various frequencies. A probe for the vanA gene hybridized to the plasmids of 23 isolates and to the chromosomes of 72 isolates. A probe for the vanB gene hybridized to the chromosomes of 8 isolates. The results of this study suggest inter- and intrahospital dissemination of vancomycin-resistant E. faecium strains over a 6-year period in southeastern Michigan. The majority of isolates studied belonged to the same few PFGE strains, indicating that clonal dissemination was responsible for most of the spread of resistance that occurred.

Anti-Bacterial Agents↗
PubMed1998

Role for parathyroid hormone in mechanical responsiveness of rat bone.

We investigated the relationship between parathyroid hormone (PTH) and mechanical stimulation in mechanically induced osteogenesis. In normal rats, mechanical stimulation of the eight caudal vertebra induced an osteogenic response. This was augmented by a single injection of human PTH-(1-34) 30-45 min before loading. No osteogenic response was seen in thyroparathyroidectomized (TPTX) rats; the osteogenic response was restored by a single injection of PTH before stimulation, suggesting that physiological levels of PTH are necessary for the mechanical responsiveness of bone. c-fos expression was detected only in the osteocytes of those rats that were both mechanically stimulated and given PTH. This suggests that PTH supports mechanically induced osteogenesis by sensitizing either the strain-sensing mechanism itself or early responses of bone to strain-generated signals. The osteogenic response was not augmented by two further daily injections of PTH and was not seen in TPTX rats in which PTH administration was started 3 days after loading. These results reveal a major role for PTH in the mechanical responsiveness of rat bone.

Animals↗
PubMed1998

Mechanical loading stimulates bone formation by reactivation of bone lining cells in 13-week-old rats.

The bone formation that occurs in response to mechanical stimulation is generally considered to be a means by which bone adapts to changes in its mechanical environment. We have previously shown that the expression of genes for bone matrix proteins is maximal 72 h after a single 5-minute episode of loading of tail vertebrae of 13-week-old female rats, that the predominant increase in mineralization occurs after 3 days, and that the osteogenic response to mechanical stimulation is not dependent on prior bone resorption. We have now investigated the cellular correlates of this osteogenic response. No proliferation was detected, by pulse or flash labeling, in the trabecular bone surface cells of animals killed 1 h to 10 days after the loading episode. Ultrastructural examination revealed that most of the cells covering the trabecular bone surface of control vertebrae were flat bone lining cells. After mechanical stimulation, the trabecular bone surface cells developed ultrastructural features of osteoblastic differentiation and activity, with acquisition of an increasingly cuboidal shape, rounded nuclei, and abundant rough endoplasmic reticulum. Morphometric analysis of the mean cell area, mean nuclear area, and cell and nuclear height showed that they were all maximal 48 h after loading. By 120 h after loading, the appearances of bone surface cells had reverted to those of control vertebrae. Thus, mechanical loading appears to activate lining cells, with a temporal sequence that correlates with bone matrix production.

Analysis of Variance↗
PubMed1998

Role of nitric oxide and prostaglandins in mechanically induced bone formation.

We have previously shown that prostaglandins (PG) and nitric oxide (NO) are required in the induction of bone formation by mechanical stimulation. We therefore tested the ability of NO donors, S-nitroso-N-acetyl-D,L-penicillamine (SNAP), and S-nitroso-glutathione (GSNO) to mimic or augment the osteogenic response of bone to a minimal mechanical stimulus. In rats administered vehicle or the vasodilator hydralazine, stimulation of the 8th caudal vertebra increased bone formation. In animals treated with SNAP or GSNO, there was significant potentiation of this osteogenic response. The bone formation rate in nonloaded vertebrae was unaffected by administration of the NO donors. We also found that while inhibition of either PG or NO production at the time of loading caused a partial suppression of c-fos mRNA expression in the loaded vertebrae, administration of indomethacin and NG-monomethyl-L-arginine together markedly suppressed c-fos expression. This suggests that although both PG and NO are required in mechanically induced osteogenesis, they appear to be generated largely independently of each other. Moreover, while exogenous NO potentiates the stimulatory effect of mechanical loading on bone formation, the lack of effect in nonloaded vertebrae suggests that NO is necessary but not sufficient for induction of bone formation.

Animals↗
PubMed1998

Legionella: a major opportunistic pathogen in transplant recipients.

Legionella have a predilection for infecting immunocompromised patients, and transplant recipients have the highest risk. Legionella spp have been the most common cause of nosocomial pneumonia among transplant recipients at selected medical centers. Diagnosis is dependent on the ability of the clinical microbiology laboratory to isolate the organism by culture; therefore, the disease is easily overlooked. The mode of transmission of Legionella pneumophila is likely aspiration in transplant recipients. Clinical manifestations are similar to that of other bacterial pneumonias, although diarrhea is often prominent. The quinolone antibiotics (especially ciprofloxacin) are the antibiotics of choice because, unlike the macrolides or rifampin, they do not interact with the immunosuppressive agents used to counter rejection. Prevention of nosocomial legionellosis involves disinfection of the hospital's potable water system. Effective disinfection methods include superheat and flush or copper-silver ionization; hyperchlorination is no longer recommended. Routine culture surveillance directed at the hospital water supply for Legionella is mandatory in hospitals caring for transplant patients.

Humans↗