Biomedical subjects

J W Chow

Publications and source records attributed to J W Chow.

At least 19 recordsLinked to original sources

PubMed2003

Effect of ball size on player reaction and racket acceleration during the tennis volley.

The purpose of this study was to examine the effect of ball size on reaction time (from ball projection to initial racket movement), movement time (from ball projection to ball-racket impact), mean rectified acceleration and vibration frequency of the racket during the impact phase (100 ms duration after ball-racket impact) of the tennis volley. Twenty-nine beginning to intermediate level tennis players performed volleys under 18 experimental conditions including variations in lateral contact location (forehand and backhand), ball type (Penn oversize, Wilson oversize, regular size), and ball speed (fast, medium, slow). A ball machine was shielded so that the subjects could not predict the ball trajectory before it was released from the machine. Outcome measures were determined using a miniature uni-axial accelerometer and a Photogate timing device. ANOVA with repeated measures and Tukey's post hoc tests were used in statistical analyses (p < .025). The reaction times for the fast speed were significantly shorter than the corresponding times for the slow speed and the reaction times for the forehand volley were significantly shorter than that of the backhand volley. The significant interaction in movement time between ball speed and ball type indicates that the benefits of the larger ball (to slow the game down) increase as the ball speed increases. No significant effect of ball type or ball speed, or interactions were found on mean rectified acceleration and vibration frequency. These results suggest that oversized balls would not cause an increased load to the hitting arm while executing a tennis volley.

Acceleration↗

PubMed2003

Lower trunk muscle activity during the tennis serve.

Prior electromyographic (EMG) analyses of the tennis serve have focused on the muscles in the hitting arm and shoulder region. This preliminary study aimed to examine the muscle activation patterns of selected lower trunk muscles during three different types of tennis serve--flat, topspin, and slice. Five male highly skilled tennis players completed 10 trials for each type of serve. Surface EMG electrodes were used to monitor the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and lumbar erector spinae (ES) muscles. For each subject, the two trials with the highest self-reported ratings were analysed. Average EMG levels during each phase of a tennis serve for each muscle were analysed using a non-parametric ANOVA design. No major differences in muscle activation pattern were found across different serve types, and bilateral differences in muscle activation were more pronounced in RA and EO than in IO and ES muscles. The abdominal muscles were more active in the topspin than in the other two types of serves during the upward swing of the racket. An appreciable amount of abdominal/low back and bilateral co-activation was observed during certain phases of the serve. The co-activation of lower trunk muscles may help to stabilise the lumbar spine during the arch back and forward swing phases of the serve. The results reinforce the importance of abdominal and low back exercises in the strength and rehabilitation programs designed for tennis players.

Abdomen↗

PubMed2003

Molecular characterization of gentamicin-resistant Enterococci in the United States: evidence of spread from animals to humans through food.

We evaluated the molecular mechanism for resistance of 360 enterococci for which the gentamicin MICs were >/=128 micro g/ml. The aac(6')-Ie-aph(2")-Ia, aph(2")-Ic, and aph(2")-Id genes were identified by PCR in isolates from animals, food, and humans. The aph(2")-Ib gene was not identified in any of the isolates. Two Enterococcus faecalis isolates (MICs > 1,024 micro g/ml) from animals failed to generate a PCR product for any of the genes tested and likely contain a new unidentified aminoglycoside resistance gene. Pulsed-field gel electrophoresis (PFGE) analysis showed a diversity of strains. However, 1 human and 18 pork E. faecalis isolates from Michigan with the aac(6')-Ie-aph(2")-Ia gene had related PFGE patterns and 2 E. faecalis isolates from Oregon (1 human and 1 grocery store chicken isolate) had indistinguishable PFGE patterns. We found that when a gentamicin-resistant gene was present in resistant enterococci from animals, that gene was also present in enterococci isolated from food products of the same animal species. Although these data indicate much diversity among gentamicin-resistant enterococci, the data also suggest similarities in gentamicin resistance among enterococci isolated from humans, retail food, and farm animals from geographically diverse areas and provide evidence of the spread of gentamicin-resistant enterococci from animals to humans through the food supply.

Animal Diseases↗

PubMed2001

Determinants of vancomycin resistance and mortality rates in enterococcal bacteremia. a prospective multicenter study.

BACKGROUND: Enterococcus species are major nosocomial pathogens and are exhibiting vancomycin resistance with increasing frequency. Previous studies have not resolved whether vancomycin resistance is an independent risk factor for death in patients with invasive disease due to Enterococcus species or whether antibiotic therapy alters the outcome of enterococcal bacteremia. OBJECTIVE: To determine whether vancomycin resistance is an independent predictor of death in patients with enterococcal bacteremia and whether appropriate antimicrobial therapy influences outcome. DESIGN: Prospective observational study. SETTING: Four academic medical centers and a community hospital. PATIENTS: All patients with enterococcal bacteremia. MEASUREMENTS: Demographic characteristics; underlying disease; Acute Physiology and Chronic Health Evaluation (APACHE) II scores; antibiotic therapy, immunosuppression, and procedures before onset; and antibiotic therapy during the ensuing 6 weeks. The major end point was 14-day survival. RESULTS: Of 398 episodes, 60% were caused by E. faecalis and 37% were caused by E. faecium. Thirty-seven percent of isolates exhibited resistance or intermediate susceptibility to vancomycin. Twenty-two percent of E. faecium isolates showed reduced susceptibility to quinupristin-dalfopristin. Previous vancomycin use (odds ratio [OR], 5.82 [95% CI, 3.20 to 10.58]; P < 0.001), previous corticosteroid use (OR, 2.43 [CI, 1.22 to 4.86]; P = 0.01), and total APACHE II score (OR, 1.06 per unit change [CI, 1.02 to 1.10 per unit change]; P = 0.003) were associated with vancomycin-resistant enterococcal bacteremia. The mortality rate was 19% at 14 days. Hematologic malignancy (OR, 3.83 [CI, 1.56 to 9.39]; P = 0.003), vancomycin resistance (OR, 2.10 [CI, 1.14 to 3.88]; P = 0.02), and APACHE II score (OR, 1.10 per unit change [CI, 1.05 to 1.14 per unit change]; P < 0.001) were associated with 14-day mortality. Among patients with monomicrobial enterococcal bacteremia, receipt of effective antimicrobial therapy within 48 hours independently predicted survival (OR for death, 0.21 [CI, 0.06 to 0.80]; P = 0.02). CONCLUSIONS: Vancomycin resistance is an independent predictor of death from enterococcal bacteremia. Early, effective antimicrobial therapy is associated with a significant improvement in survival.

APACHE↗

PubMed2001

Biomechanical comparison of two racing wheelchair propulsion techniques.

PURPOSE: The purpose was to compare the conventional (CVT) and para-backhand (PBT) techniques used for racing wheelchair propulsion. Selected 3-D kinematic characteristics of the upper body and the electromyographic (EMG) signals of selected muscles during racing wheelchair propulsion over a roller system were examined. METHODS: Eight CVT and seven PBT elite performers served as the subjects. Each subject performed maximum effort pushing for 30 s at a load that simulated overground pushing. Two S-VHS camcorders (60 Hz) were used to obtain 3-D kinematic parameters and muscle activity was monitored using surface electrodes. RESULTS: The CVT was found to have significant shorter push time, smaller relative push time, and greater relative recovery time than the PBT. The CVT is a more compact stroke (smaller joint range of motion) and the PBT has a faster overall movement speed. Significant differences in arm positions were found between the two techniques at the instants of hand contact and hand release, and the upper arm was more internally rotated at these two instants in the CVT when compared with the PBT. The EMG data showed that large variations in muscle activation patterns existed in each technique group. In general, the flexor carpi radialis and triceps brachii were most active in the push phase. The upper trapezius and postero-middle deltoids were most active in the ascending recovery phase, whereas the extensor carpi radialis, biceps brachii, antero-middle deltoids, and pectoralis major were most active during the descending recovery phase. CONCLUSIONS: The greater push time and push angle associated with the PBT suggest that the PBT may be more suitable for endurance athletes who are less explosive in their pushing strokes. The greater time and angle allow PBT users the opportunity to transmit more force to the wheel.

Adult↗

PubMed2001

Aminoglycoside resistance genes aph(2")-Ib and aac(6')-Im detected together in strains of both Escherichia coli and Enterococcus faecium.

Escherichia coli SCH92111602 expresses an aminoglycoside resistance profile similar to that conferred by the aac(6')-Ie-aph(2")-Ia gene found in gram-positive cocci and was found to contain the aminoglycoside resistance genes aph(2")-Ib and aac(6')-Im (only 44 nucleotides apart). aph(2")-Ib had been reported previously in Enterococcus faecium SF11770. aac(6')-Im had not been detected previously in enterococci and was found to be present also 44 nucleotides downstream from aph(2")-Ib in E. faecium SF11770. aph(2")-Ib and aac(6')-Im are separate open reading frames, each with its own putative ribosome binding site, whereas aac(6')-Ie-aph(2")-Ia appears to be a fusion of two genes with just one start and one stop codon. The deduced AAC(6')-Im protein exhibits 56% identity and 80% similarity to the AAC(6')-Ie domain of the bifunctional enzyme AAC(6')-APH(2"). Our results document the existence of a member of the aph(2") family of genes in gram-negative bacteria and provide evidence suggesting the horizontal transfer of aph(2")-Ib and aac(6')-Im as a unit between gram-positive and gram-negative bacteria.

Aminoglycosides↗

PubMed2001

Heteroresistance to vancomycin in Enterococcus faecium.

This study presents the first report of vancomycin heteroresistance in an Enterococcus faecium isolate from a patient. The original isolate was susceptible in vitro to vancomycin. E-tests showed growth of subcolonies in a zone of inhibition with a vancomycin MIC of >256 microg/ml. Both the susceptible and resistant colonies were from the same strain as determined by PFGE, and both contained the vanA gene as determined by PCR.

Anti-Bacterial Agents↗

PubMed2000

Aminoglycoside resistance in enterococci.

High-level aminoglycoside resistance in enterococci is mediated generally by aminoglycoside-modifying enzymes, which eliminate the synergistic bactericidal effect usually seen when a cell wall-active agent is combined with an aminoglycoside. Clinical microbiology laboratories currently screen for aminoglycoside resistance in enterococci by testing gentamicin and streptomycin susceptibility. If the recently detected aminoglycoside resistance genes, aph(2")-Ib, aph(2")-Ic, and aph(2")-Id, become more prevalent among clinical isolates, the approach for detecting susceptibility to aminoglycoside synergism in enterococci will require modification. More potent aminoglycosides need to be developed that will be resistant to modification by a broad spectrum of aminoglycoside-modifying enzymes present in enterococci.

Anti-Bacterial Agents↗

PubMed2000

Treatment with fluoride or bisphosphonates prevents bone loss associated with colitis in the rat.

Idiopathic inflammatory bowel disease (IBD) is associated with osteoporosis in over 30% of cases. We have previously shown that 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced colitis in rats is associated with considerable bone loss. In the current study we tested the ability of sodium fluoride (NaF) or the bisphosphonate pamidronate to prevent the bone loss associated with TNBS-induced colitis in 22-week-old male Wistar rats. As previously found, there was a 43% decrease in cancellous bone volume in rats with TNBS-induced colitis after 4 weeks. This was associated with marked suppression of the bone formation rate to less than 25% of control animals. Treatment with NaF had no effect on the severity of colitis, but the bone volume and bone formation rate were increased to levels indistinguishable from those of control animals. In animals treated with pamidronate, cancellous bone volume was also restored to that of control animals despite persistence of the colitis. In these animals there was marked suppression of bone formation, associated with suppression of bone resorption. This data shows the bone loss associated with colitis may be prevented by treatment with NaF or bisphosphonates without requiring improvement in severity of the colitis.

Animals↗

PubMed2000

Effect of resistance load on biomechanical characteristics of racing wheelchair propulsion over a roller system.

The purpose of this study was to examine how resistance load influenced the kinematic characteristics and the activity of selected muscles (flexor and extensor carpi radialis, biceps brachii, triceps brachii, antero-middle and postero-middle deltoids, pectoralis major, and upper trapezius) during maximum effort racing wheelchair stroking using 3D videographic and surface EMG techniques. Fifteen male experienced wheelchair racers served as subjects and three consecutive stroke cycles were analyzed for two load conditions. In contrast to previous studies where variations in speed were a result of variations in pushing effort or disability classification, a reduction in stroking speed caused by increasing load did not result in a decrease in stroking frequency. Increases in load significantly influenced the push and recovery times but not the stroke time or frequency. The vertical ranges of motion and vertical velocities at initial hand contact of the upper extremity joints decreased significantly from light to heavy resistance conditions. These results suggest that the vertical motion is influenced greatly by the load. Various degrees of muscle co-contractions were observed in most phases of the stroke cycle. The activation pattern of the deltoid muscle was different from what has been previously reported, probably because of the exaggerated forward lean trunk position adopted by our subjects. Although the overall EMG activity remained the same or decreased when the resistance was increased, stroking under a heavy resistance load is likely to be more demanding physiologically because of the greater push time-recovery time (work-rest) ratio with increasing resistance.

Adult↗

PubMed2000

In-vitro synergistic activity of the combination of ampicillin and arbekacin against vancomycin-and high-level gentamicin-resistant Enterococcus faecium with the aph(2")-Id gene.

The combination of ampicillin plus arbekacin produced synergistic killing against 8 of 13 vancomycin-, ampicillin-, gentamicin-, and streptomycin-resistant Enterococcus faecium isolates that possess the high-level gentamicin resistance gene, aph(2")-Id. This combination may prove useful in treating infections caused by multiresistant enterococci.

Aminoglycosides↗

PubMed2000

In-vitro activity of arbekacin alone and in combination with vancomycin against gentamicin- and methicillin-resistant Staphylococcus aureus.

In-vitro susceptibility studies were performed on 99 clinical Staphylococcus aureus isolates. A total of 68 of 73 methicillin-resistant S. aureus and 2 of 26 methicillin-susceptible S. aureus were gentamicin-resistant (gentamicin MIC range 16 to 1,024 microg/mL). All 70 gentamicin-resistant isolates contained the aac(6')-Ie-aph(2'')-Ia aminoglycoside resistance gene, and none possessed the aph(2'')-Ic or aph(2'')-Id aminoglycoside resistance genes. The arbekacin MIC for the 70 gentamicin-resistant isolates ranged from 0.25 to 4 microg/mL. The combination of arbekacin plus vancomycin produced synergistic killing against 12 of 13 gentamicin-resistant MRSA isolates. The combination of gentamicin plus vancomycin produced synergistic killing against 7 of the same 13 isolates. Arbekacin may prove useful when used in combination with vancomycin in treating infections caused by gentamicin-resistant MRSA.

Aminoglycosides↗

PubMed2000

Kinematic analysis of shot-putting performed by wheelchair athletes of different medical classes.

The aim of this study was to identify those kinematic characteristics that are most closely related to an athlete's medical classification and measured distance of a put. Two S-VHS camcorders (60 fields per second) were used to record the performance of 17 males of different classes. Each participant performed six trials and the best trial for each was selected for analysis. Three-dimensional kinematics of the shot and upper body segments at the instant of release and during the forward thrust (delivery) were determined. The average speeds and angles of the shot at release for different classes (5.3-7.8 m x s(-1) and 21.2 to 34.4 degrees, respectively) were smaller than those exhibited by elite male able-bodied throwers. The height of the shot at release, the angular speed of the upper arm at release, the range of motion of the shoulder girdle during the delivery, and the average angular speeds of the trunk, shoulder girdle and upper arm during the delivery, were all significantly correlated with both the classification and measured distance (P < 0.05). The results indicate the importance of achieving a high average angular speed for each upper body segment during the delivery.

Acceleration↗

PubMed2000

Detection of the high-level aminoglycoside resistance gene aph(2")-Ib in Enterococcus faecium.

A new high-level gentamicin resistance gene, designated aph(2")-Ib, was cloned from Enterococcus faecium SF11770. The deduced amino acid sequence of the 897-bp open reading frame of aph(2")-Ib shares homology with the aminoglycoside-modifying enzymes AAC(6')-APH(2"), APH(2")-Ic, and APH(2")-Id. The observed phosphotransferase activity is designated APH(2")-Ib.

Anti-Bacterial Agents↗

PubMed2000

Efficacy of ampicillin plus arbekacin in experimental rabbit endocarditis caused by an Enterococcus faecalis strain with high-level gentamicin resistance.

Enterococcus faecalis LC40 is an ampicillin-susceptible clinical isolate with high-level gentamicin resistance due to the aac(6')-Ie-aph(2")-Ia aminoglycoside resistance gene. The combination of ampicillin plus arbekacin reduced mean bacterial vegetation counts significantly more than ampicillin alone or ampicillin plus gentamicin in a rabbit model of aortic-valve endocarditis caused by E. faecalis LC40.

Aminoglycosides↗

PubMed2000

PCR fragment length polymorphism analysis of vancomycin-resistant Enterococcus faecium.

In this study, the glycopeptide resistance element, Tn1546, in 124 VanA Enterococcus faecium clinical isolates from 13 Michigan hospitals was evaluated using PCR fragment length polymorphism. There were 26 pulsed-field gel electrophoresis (PFGE) types, which consisted of epidemiologically related and unrelated isolates from separate patients (1992 to 1996). Previously published oligonucleotides specific for regions in the vanA gene cluster of Tn1546 were used to amplify vanRS, vanSH, vanHAX, vanXY, and vanYZ. The glycopeptide resistance element, Tn1546, of E. faecium 228 was used as the basis of comparison for all the isolates in this study. Five PCR fragment length patterns were found, as follows. (i) PCR amplicons were the same size as those of EF228 for all genes in the vanA cluster in 19.4% of isolates. (ii) The PCR amplicon for vanSH was larger than that of EF228 (3.7 versus 2.3 kb) due to an insertion between the vanS and vanH genes (79.2% of isolates). (iii) One isolate in a unique PFGE group had a vanSH amplicon larger than that of EF228 (5.7 versus 2.3 kb) due to an insertion in the vanS gene and an insertion between the vanS and vanH genes. (iv) One isolate did not produce a vanSH amplicon, but when vanS and vanH were amplified separately, both amplicons were the same size as those as EF228. (v) One isolate had a vanYZ PCR product larger than that of EF228 (2.8 versus 1.6 kb). This study shows that in a majority of the VanA E. faecium isolates, Tn1546 is altered compared to that of EF228. A total of 79.2% of the study isolates had the same-size insertion between the vanS and vanH genes. The results of this study show dissemination of an altered Tn1546 in heterologous VanA E. faecium in Michigan hospitals.

Bacterial Proteins↗

PubMed2000

Simple and reliable multiplex PCR assay for surveillance isolates of vancomycin-resistant enterococci.

Conditions have been optimized for the use of a multiplex PCR for the detection of vancomycin-resistant enterococci in nosocomial surveillance specimens. Seven primer sets targeting the genes vanA, vanB, vanC1, vanC2/C3 Enterococcus faecalis-specific, Enterococcus faecium-specific, and rrs (16S rRNA) were used in one reaction tube. The PCR method developed in the present study is simple and reliable for the rapid characterization of vancomycin-resistant enterococci.

Cross Infection↗

PubMed2000

Role of nitric oxide and prostaglandins in the bone formation response to mechanical loading.

Nitric oxide and prostaglandins are crucial early mediators in mechanically induced bone formation. They are also responsible for the associated induction of gene expression of c-fos and IGF-1 in osteocytes, key mechanosensory cells in bone. Insight into the cellular and molecular mechanisms underlying bone formation has important implications for the maintenance of structural competence of bone.

Animals↗