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Biomedical subjects

P Marks

Publications and source records attributed to P Marks.

At least 19 recordsLinked to original sources
PubMed2006

A new look into kicking a football: an investigation of muscle activity using MRI.

The kicking action predominantly used in Australian Rules football is considered to be responsible for many lower limb injuries. The aim of this study was to describe a non-invasive method of identifying the thigh muscles involved in kicking an Australian Rules football, using MRI. Both upper thighs of 10 recreational footballers were examined using a 1.5-T General Electric MRI scanner before and immediately after carrying out a set kicking exercise protocol. The signal intensity (SI) changes in 14 individual muscles were investigated using a standardized region of interest to determine the levels of muscle activity. Significant SI changes were observed in several muscles of the kicking and stance legs among all participants. In the kicking leg, the greatest SI changes were observed in the adductor longus and tensor fascia latae muscles (49.38% (+/-8.95) and 45.47% (+/-7.91), respectively; P < 0.05), whereas in the stance leg, the muscles displaying the highest changes were the semitendinosus and tensor fascia latae muscles (46.48% (+/-9.97) and 33.68% (+/-8.36), respectively; P < 0.05). This study has shown that MRI can be useful for observing the activity of individual muscles in the upper thigh during the kicking motion. This non-invasive approach provides a detailed analysis of anatomy and emphasizes the muscles at high risk of injury.

Adult↗
PubMed2005

The electromechanics of DNA in a synthetic nanopore.

We have explored the electromechanical properties of DNA on a nanometer-length scale using an electric field to force single molecules through synthetic nanopores in ultrathin silicon nitride membranes. At low electric fields, E < 200 mV/10 nm, we observed that single-stranded DNA can permeate pores with a diameter >/=1.0 nm, whereas double-stranded DNA only permeates pores with a diameter >/=3 nm. For pores <3.0 nm diameter, we find a threshold for permeation of double-stranded DNA that depends on the electric field and pH. For a 2 nm diameter pore, the electric field threshold is approximately 3.1 V/10 nm at pH = 8.5; the threshold decreases as pH becomes more acidic or the diameter increases. Molecular dynamics indicates that the field threshold originates from a stretching transition in DNA that occurs under the force gradient in a nanopore. Lowering pH destabilizes the double helix, facilitating DNA translocation at lower fields.

Biophysics↗
PubMed2005

A randomized trial of ultrasound-guided brachial plexus anaesthesia in upper limb surgery.

Ultrasound guidance allows real-time identification of relevant anatomy and needle position when performing brachial plexus regional anaesthesia. The aim of this investigation was to determine whether the use of surface ultrasound could improve the quality of brachial plexus anaesthesia for upper limb surgery. Forty patients were randomized to either conventional "landmark-based" plexus anaesthesia, or to an ultrasound-guided approach using a 13 mHz linear array transducer Both interscalene and axillary techniques were used. The use of ultrasound significantly improved the onset and completeness of sensory (P=0.011) and motor (P=0.002) block. Ultrasound guidance also significantly reduced (P=0.012) the incidence of paraesthesia during the performance of the blocks. Ultrasound guidance increases the quality of sensory and motor blockade in brachial plexus regional anaesthesia, and by reducing the incidence of paraesthesia during performance of the blocks, may confer greater safety.

Analysis of Variance↗
PubMed2004

Adhesion of Staphylococcus to orthopaedic metals, an in vivo study.

This study describes a new model of biofilm study in rabbits. The primary focus of this study was to assess biofilm adhesion to orthopaedic metals in their first 48 h in a femoral intramedullary implantation model. Two previous inoculation methods i.e. that of pre- and direct inoculation were studied with two bacterial isolates namely Staphylococcus aureus and epidermidis, on titanium and stainless steel metallic implants. A method of sonication and log dilution/plating was used to assess biofilm bacteria adhering to implants. Silver coated metals were then compared with their respective control metals in the new model. The direct inoculation model gave larger and more reproducible biofilm adhesion to implanted metals. Staphylococcus epidermidis shows lower adhesion ability to metals, and biofilms adhere in greater numbers to stainless steel over titanium. Silver coated metals show no statistical difference over control metals when exposed to orthopaedic biofilms.

Animals↗
PubMed2003

Etiology and risk factors of 339 cases of infective endocarditis: report from a 10-year national prospective survey in the Slovak Republic.

The authors studied the etiology, outcome and risk factors of 339 cases of infective endocarditis (IE) in Slovakia over the last 10 years. Aortic valve was infected in 59.9%, mitral in 38.1% and tricuspidal/pulmonary in 5.0% of cases. The majority of IE were caused by staphylococci (29.2%), 15.0% were due to viridans streptococci, 7.4% due to Enterococcus faecalis, 3.9% due to the HACEK group (Haemophilus spp., Actinobacillus spp., Corynebacterium spp., Eikenella spp., Kingella spp.) and 39.2% were culture negative. The following risk factors were the most frequently identified: rheumatic fever in 24.2%, dental surgery in 13.3%, previous cardiosurgery in 7.1% and neoplasia in 7.1%. All patients were treated with antimicrobials and 42.5% of patients also with surgery (valvular prosthesis replacement): 61 (18.0%) died, and 278 (82.0%) survived at day 60 after the diagnosis of endocarditis was made. Univariate analysis did not show significant differences in most of the recorded risk factors between patients who died and those who survived: apart from staphylococcal etiology (44.3% vs. 26.6%, P < 0.01), persistent bacteremia (with three or more positive blood cultures 24.6% vs. 9.7% P < 0.002) which were significantly associated with higher attributable mortality, as was absence of surgery (55.7% vs. 6.1% P < 0.001), whereas antibiotic therapy in combination with surgery significantly predicted better outcome (P < 0.001). We compared risk factors, etiology, therapeutic strategies and outcome of IE in two periods: from 1991-1997 (180 cases) and from 1998-2001 (159 cases). Rheumatic fever was less commonly observed in second period (1998-2001) P < 0.01 since its prevalence in Slovakia is rapidly decreasing. Dental surgery was less frequent as well (20.5% vs. 5.0% P < 0.001). There was a significant shift in etiology within the second study period: negative-culture endocarditis (despite better bacteriological techniques) (P < 0.001) was more frequently observed in the 1st period and represented 53.3% of all cases in 1998-2001 in comparison to 26.7% in 1991-1997. Enterococci (P < 0.0002) were also more frequent in the 2nd period. Persistent bacteremia (3 or more positive blood cultures 20.5% vs. 3.1%, P < 0.001 was less commonly observed within the 2nd period (1998-2001) in comparison to 1991-1997. More patients in the second period (1998-2001) had complications of IE (P < 0.001) than in the 1st period. However mortality was lower (22.2% vs. 13.2%, P < 0.044) because of more surgical intervention in the 2nd period (52.8% vs. 33.3%, P < 0.001).

Adult↗
PubMed2001

Production and characterization of an antiserum which recognizes the native receptor for thyrotropin-releasing hormone.

Despite attempts in several laboratories, it has been difficult to prepare antiserum to the thyrotropin-releasing hormone receptor (TRHR). We have prepared a polyclonal anti-rat TRHR antiserum by immunization of rabbits with a synthetic peptide corresponding to the C-terminus of the TRHR. The specificity of the antiserum was assessed by enzyme-linked immunosorbent assay. The affinity-purified antibody recognized a major broad band at 50-60 kDa and a minor broad band at 100-120 kDa in Western blot analysis of membrane proteins from TRHR-transfected, but not control, HEK293t cells. Binding to both bands was abolished by preincubation with the immunizing peptide but not control peptide. The approach was repeated with rat pituitary F4C1 cells, which lack endogenous TRHRs; membranes from F4C1 cells transfected with TRHR cDNA, but not control cells, showed specific binding by Western blot. Using laser confocal microscopy, the TRHR was visualized on the plasma membrane of transfected, but not control, F4C1 cells. Similar confocal findings were observed in TRHR-transfected HEK293t cells. Within 5 min after TRH addition, the TRHR signal translocated from the plasma membrane to the cytoplasm of F4C1 cells transfected with TRHR cDNA. Ten minutes after TRH addition, the TRHR signal formed aggregates in the cytoplasm. Thirty minutes after TRH treatment, both cytoplasmic and plasma membrane localizations were observed, suggesting recycling of some TRHRs back to the plasma membrane. These observations are consistent with our previous findings using an epitope-tagged TRHR. In conclusion, we have prepared an antiserum that recognizes the native TRHR by Western blot analysis and confocal microscopy.

Animals↗
PubMed2001

Histone deacetylases and cancer: causes and therapies.

Together, histone acetyltransferases and histone deacetylases (HDACs) determine the acetylation status of histones. This acetylation affects the regulation of gene expression, and inhibitors of HDACs have been found to cause growth arrest, differentiation and/or apoptosis of many tumours cells by altering the transcription of a small number of genes. HDAC inhibitors are proving to be an exciting therapeutic approach to cancer, but how do they exert this effect?

Acetylation↗
PubMed2001

Ependymoma of the neurohypophysis.

There are two reported cases of ependymomas arising in the pituitary fossa; one in a human, the other in a horse. Both died during their stay in hospital. The case presented here is the first published case of a patient who is well 3 months after surgery.

Diagnosis, Differential↗
PubMed2001

Safety, efficacy and acceptability of a new power toothbrush: a 3-month comparative clinical investigation.

PURPOSE: To compare the safety and efficacy of a new power toothbrush (Braun Oral-B D17) with an ADA reference manual toothbrush. MATERIALS AND METHODS: 110 healthy subjects, 18-65 yrs of age, with a mean plaque index of > or = 1.80 and a gingival index of > or = 1.00, were enrolled in this 3-month, randomized, parallel-group, examiner-blind study. Oral soft and hard tissues were examined for safety, and plaque, gingivitis and bleeding were measured to evaluate efficacy. Measurements were made at baseline and after 1 and 3 months of product use. Following the baseline visit and randomization, subjects were instructed to brush twice daily for 2 mins with their assigned brush. RESULTS: 101 subjects completed the study with evaluable data for all time periods, 52 in the D17 group and 49 in the manual group. None of the nine withdrawals from the study were related to product use and no product-related adverse effects were reported. There was no clinically significant soft or hard tissue abrasion observed at any time point in either group. After 1 and 3 months, significant reductions from baseline in whole mouth and interproximal plaque, gingivitis and bleeding were observed in both groups. A comparison of the two groups revealed that the whole mouth and approximal plaque indices were reduced to a significantly greater extent in the D17 group after both 1 and 3 months. The whole mouth gingival index was also reduced to a greater extent in the D17 group at 1 and 3 months, but a difference in the approximal gingival index was only apparent after 3 months. With respect to the bleeding index, there was a significant difference between the two groups for the whole mouth at both 1 and 3 months, but the differences in favor of the D17 for approximal values did not achieve statistical significance. In conclusion, the D17 was found to be safe and had increased efficacy with respect to reduction of plaque and gingivitis, compared with a manual toothbrush.

Adolescent↗
PubMed2000

Use of a non-penetrating staple device for spinal dural closure.

Closure of the spinal dura by suture can be technically demanding and a watertight closure is rarely achieved. A method of dural closure using non-penetrating staples is described which permits rapid watertight closure of the dura even in confined spaces.

Dura Mater↗
PubMed2000

Acute neurologic deterioration following lumbar puncture in an epidural abscess occurring 14 months after epidural catheter placement.

We report the case of a 19-year-old girl admitted to the hospital with a 2-month history of back pain and a 1-week history of severe weakness, who underwent a diagnostic lumbar puncture which was swiftly followed by acute neurologic deterioration requiring ventilation. She was subsequently shown to have an epidural abscess extending from the second cervical to the fifth lumbar vertebrae. She had received uneventful epidural analgesia for childbirth 14 months previously. The case is unusual in both the acute deterioration following lumbar puncture, and also in the length of time from epidural siting to abscess formation, if this were indeed the source of the infection.

Adult↗
PubMed2000

Impact of heterogeneity within cultured cells on bacterial invasion: analysis of Pseudomonas aeruginosa and Salmonella enterica serovar typhi entry into MDCK cells by using a green fluorescent protein-labelled cystic fibrosis transmembrane conductance regulator receptor.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride ion channel that also serves as a receptor for entry of Pseudomonas aeruginosa and Salmonella enterica serovar Typhi into epithelial cells. To evaluate heterogeneity in CFTR protein expression in cultured cells and the effect of heterogeneity on internalization of different P. aeruginosa and serovar Typhi strains, we used two-color flow cytometry and confocal laser microscopy to study bacterial uptake by Madin-Darby canine kidney (MDCK) type I epithelial cells stably expressing a green fluorescent protein (GFP)-CFTR fusion construct (MDCK-GFP-CFTR cells). We found a strong correlation between cell size and GFP-CFTR protein expression, with 60 to 70% of cells expressing low levels of GFP-CFTR protein, 20 to 30% expressing intermediate levels, and <10% expressing high levels. The cells were sorted into low-, intermediate-, or high-level producers of CFTR protein; in vitro growth of each sorted population yielded the same distribution of CFTR protein expression as that in the original population. Cells expressing either low or high levels of CFTR protein internalized bacteria poorly; maximal bacterial uptake occurred in the cells expressing intermediate levels of CFTR protein. Treatment of MDCK cells with sodium butyrate markedly enhanced the production of CFTR protein without increasing cell size; butyrate treatment also increased the proportion of cells with internalized bacteria. However, there were fewer bacteria per butyrate-treated cell and, for P. aeruginosa, there was an overall decrease in the total level of bacterial uptake. The most highly ingested bacterial strains were internalized by fewer total MDCK-GFP-CFTR cells, indicating preferential bacterial uptake by a minority of epithelial cells within a given culture. Confocal fluorescence microscopy showed that P. aeruginosa and serovar Typhi induced cytoplasmic accumulation of CFTR protein close to the plasma membrane where the bacteria were adherent. These results show that within a population of MDCK-GFP-CFTR cells, there are cells with markedly different abilities to ingest bacteria via CFTR, the majority of the P. aeruginosa and serovar Typhi cells are ingested by the one-fourth to one-third of the cells that exhibit an intermediate size and level of CFTR protein expression, and overexpression of the CFTR receptor does not increase total bacterial uptake but rather allows more epithelial cells to ingest fewer total bacteria.

Animals↗