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Biomedical subjects

W Schenk

Publications and source records attributed to W Schenk.

At least 19 recordsLinked to original sources
PubMed2001

Atypical hamstrings electromyographic activity as a compensatory mechanism in anterior cruciate ligament deficiency.

Anterior cruciate ligament (ACL) deficiency may cause functional instability of the knee (noncopers), while other patients compensate and perform at the same level as before injury (copers). This pilot study investigated whether there is a compensatory electromyographic (EMG) activity of the hamstrings in copers, noncopers and control patients. Ten patients with an ACL deficiency were equally divided into two groups of copers and noncopers. All patients underwent gait analysis with EMG of six muscles around the knee. Ten healthy young men formed the control group. In contrast to noncopers, copers showed an atypical semitendinosus activity during stance phase; the corresponding trend was found in biceps femoris activity. There was no difference between copers and controls in knee extension during stance phase. The noncopers had less knee extension. Atypical hamstring muscle activity may thus be a compensatory mechanism by which copers enable themselves to perform on a normal level.

Adaptation, Physiological↗
PubMed2001

Staphylococcus aureus biofilm formation on different gentamicin-loaded polymethylmethacrylate bone cements.

In this in vitro study, the formation of a Staphylococcus aureus biofilm on six gentamicin-loaded bone cements (CMW1, CMW3, CMW Endurance, CMW2000, Palacos, and Palamed) was determined in a modified Robbins device over a 3 days time span and related with previously (Van de Belt et al., Biomaterials 21 (2000) 1981) measured kinetics of antibiotic release by these cement brands. The influence of gentamicin release on biofilm formation was quantified by expressing the number of colony-forming units on gentamicin-loaded cement relative to the number of viable organisms on unloaded cement of the same brand. Biofilms formed on all gentamicin-loaded cements, despite the release of antibiotics, followed a consistent pattern in time with a maximum number of colony-forming units per unit cement area found between 24 and 30 h after inoculation. None of the gentamicin-loaded cements showed a reduction in biofilm formation relative to unloaded cements within 6 h after inoculation, whereas only gentamicin-loaded CMW1 and Palacos reduced biofilm formation 24 h after inoculation. Alternatively, CMW Endurance, CMW2000, and Palamed did not exhibit any initial reductions in biofilm formation, but effects started after 72, 48, and 72 h, respectively. Biofilm reduction by gentamicin-loaded CMW3 lasted the longest from 24 to 72 h. Interestingly, each cement seemed to have a different "window-of-effectiveness" with regard to reduction in biofilm formation that did not relate with the gentamicin-release kinetics. Summarising, this study demonstrates that although gentamicin loading of bone cements yields reductions in biofilm formation, S. aureus is able to grow on gentamicin-loaded bone cements.

Biocompatible Materials↗
PubMed2001

Infection of orthopedic implants and the use of antibiotic-loaded bone cements. A review.

Infections by bacteria are a serious complication following orthopedic implant surgery, that can usually only be cured by removing the implant, since the biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. Over the past few decades, attempts have been made to prevent and cure orthopedic implant infections by incorporating antibiotics in polymethylmethacrylate bone cements, in primary and revision surgery. However, the clinical efficacy of antibiotic-releasing bone cements is not accepted by all and the long-term exposure to low doses from antibiotic-releasing bone cements in patients is strongly related to the emerging threat of antibiotic resistance in medicine today. In this article, we start by reviewing the mechanisms governing the formation of an infectious biofilm on orthopedic implant materials, the release mechanisms and properties of clinically-used, antibiotic-loaded bone cements. The clinical efficacy of antibiotic-loaded bone cements is evaluated analyzing separatedly the prophylactic and therapeutic uses of these products.

Antibiotic Prophylaxis↗
PubMed2000

Surface roughness, porosity and wettability of gentamicin-loaded bone cements and their antibiotic release.

In this study, the release of gentamicin as a function of time was measured for six different gentamicin-loaded bone cements and related with the surface roughness, porosity and wettability of the cements. Initial release rates varied little between the six bone cements (CMW1, CMW3, CMW Endurance, CMW 2000, Palacos, and Palamed) and ranged from 8.6 to 14.1 microg/cm2/h. The total amounts of gentamicin released after 1 week varied between 4.0 and 5.3% of the total amount of antibiotic incorporated for the CMW cements and was 8.4% for Palacos. Palamed released after 1 week significantly more of the gentamicin incorporated (17.0%). The wettability of all cements was similar (water contact angles between 70 and 80 degrees), but the surface roughness and the porosity of the cements varied markedly. Initial release rates increased with surface roughness, although the correlation coefficient was low (0.64), while total amounts released increased linearly (correlation coefficient 0.97) with the bulk porosity of the cements. Consequently, it can be concluded that the release kinetics of gentamicin from bone cements is controlled by a combination of surface roughness and porosity.

Bone Cements↗
PubMed2000

Gentamicin release from polymethylmethacrylate bone cements and Staphylococcus aureus biofilm formation.

We measured the formation of a Staphylococcus aureus biofilm in vitro on unloaded and gentamicin-loaded bone cements (CMW3 and Palacos R) and related the formation to antibiotic release rates. All experiments were done in triplicate. Microbial growth on gentamicin-loaded cements occurred despite the release of antibiotic. Biofilm formation on gentamicin loaded CMW3 bone cement was one fourth to one fifth less than on the unloaded bone cement, while biofilm formation on Palacos R bone cement was not significantly affected by antibiotic loading. More gentamicin was released from CMW3 (79 mg) than from Palacos R (70 mg), but the percentage gentamicin released after one week relative to the total amount incorporated was significantly lower for CMW3 (4.7%) than for Palacos R (8.4%). After one day, subinhibitory concentrations of antibiotics were eluted from the cements. We concluded that antibiotic-loaded bone cement does not necessarily inhibit the formation of an infectious biofilm in vitro.

Anti-Bacterial Agents↗
PubMed1991

The effects of thyroid state on sarcomere dynamics of ventricular cells and contraction of papillary muscles in the rat heart.

Diastolic sarcomere length, amplitude of maximal sarcomere shortening, maximal rate of sarcomere shortening, maximal rate of sarcomere re-lengthening, time to peak sarcomere shortening and trans-sarcolemmal ion currents were measured in isolated ventricular cells from euthyroid, hypothyroid and hyperthyroid rats. The data were compared with the developed tension and time to peak tension of papillary muscles. The diastolic sarcomere length was not affected by the changes in thyroid state. Hypothyroidism led to an increased time to peak sarcomere shortening, an increased time to peak tension of the papillary muscle, and a depression of the maximal rates of shortening and elongation of the sarcomeres. Changes in dynamics of the sarcomere and contraction of papillary muscle did not occur in parallel under the influence of hyperthyroidism. In comparison with the euthyroid state, the time to peak tension was shortened and amplitude of shortening of the sarcomere was increased. The time to peak shortening of the sarcomere and developed tension of papillary muscle remained unaltered. In cardiac cells, hypothyroidism was associated with a decreased slow Ca2+ current and hyperthyroidism with an increased slow Ca2+ current. In contrast to euthyroid and hypothyroid cardiac cells, the hyperthyroid cardiomyocytes exhibited a trans-sarcolemmal transient inward current after repolarization. Both hypothyroidism and hyperthyroidism resulted in a depressed potentiation of sarcomere shortening and myocardial developed tension after resting.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Sarcomere dynamics in isolated cardiac myocytes investigated by high-time resolution laser light diffractometry.

Unattached single cells of the guinea pig myocardium were illuminated with laser light. From the position of the mean of the first order diffraction line at a CCD sensor the sarcomere length was calculated with a time resolution of 1 ms. The maximum velocity of the sarcomere shortening was 2.15 +/- 0.87 microns/s (mean +/- S.E.). Nearly 20% of the cells investigated were found to shorten in a stepwise manner. The intensity profiles of these myocytes deviated from the Gaussian shape at the same time as "pauses" became visible. Therefore, this phenomenon might be due to Bragg effects which result from different sarcomere populations within stepwise shortening cardiac cells.

Animals↗
PubMed1987

A study of dynamic properties in isolated myocardial cells by the laser diffraction method.

Laser diffraction patterns were investigated from enzymatically isolated, unattached myocardial cells of guinea-pigs and mice. Experiments were performed at 2.5 mM Ca2+ and room temperature. The mean sarcomere length of resting guinea-pig and mouse myocardial cells amounted to about 1.83 micron and 1.75 micron, respectively. When paced with alternating intervals by field stimulation carefully selected ventricular cells showed transient phenomena. (1) The staircase following a rested state contraction was positive in the case of guinea-pig and negative in the case of mouse myocardial cells; (2) The rested state as compared to the steady state sarcomere shortening of guinea-pig and mouse cardiac myocytes amounted to 35% and 600%, respectively; (3) The interval strength curve of guinea-pig myocardial cells passed through a maximum which was 0.26 +/- 0.06 micron (mean +/- S.D.) at a pacing interval of 2 s whereas myocardial cells of mice showed a rise of shortening with increasing intervals reaching a maximum at the rested state (0.24 +/- 0.08 micron). Results were similar to those obtained from multicellular preparations. We conclude therefore, dynamic properties of multicellular preparations are nicely reflected at the sarcomere level.

Animals↗
PubMed1987

Sarcomere dynamics by the laser diffraction method of isolated myocardial cells from guinea pigs.

The sarcomere dynamics of enzymatically isolated cardiac myocytes obtained from guinea pig ventricles was studied by the laser diffraction method (He-Ne laser, 3 mW). Unattached cells were stimulated electrically with a frequency of 0.5 s-1 thus producing stable contraction relaxation cycles for more than five minutes. The extent of shortening varied from cell to cell between 0.05 micron and nearly 0.25 micron/src (src = sarcomere) in the steady state. Starting with a rested state contraction repetitive stimulation resulted in a positive staircase and a nearly threefold extent of shortening after reaching the steady state. Synchronous contractions often consisted of two components that were changed markedly during application of ultrasound (5 W cm-2, 1 MHz). The late component disappeared completely while the first one increased continuously. Differences in extent and velocity of sarcomere shortening are probably due to different contributions of the sarcoplasmic reticulum to the total amount of calcium that controls the myofilament activation.

Animals↗
PubMed1986

Laser diffraction and speckling studies in skeletal and heart muscle.

The optical setup including a low power helium-neon laser as well as microcomputer system based U 880 for on line investigation of laser diffraction and scattering in skeletal and heart muscle is described. Frog muscle single fibres yield excellent laser diffraction patterns which are best adapted to measurements of the sarcomere dynamics. In the presence of 6 mM caffeine the diffraction disappears gradually and a moving speckle pattern occurs. Diffraction and speckle phenomena are compared of skeletal and heart muscle preparations. From autocorrelation and Fourier transformation of intensity fluctuations ("speckling") in resting mammalian cardiac muscle tissue results a favoured frequency of 1 Hz. It is supposed that clusters of sarcomeres move rhythmically but independent from each other as long as the preparation is not stimulated repetitively.

Animals↗
PubMed1985

Preserved irradiated homologous cartilage implants in canine eyelids.

Preserved irradiated homologous costal cartilage implants were placed in six canine lower lids for a period of 7-12 weeks. The three implants placed under a covering of conjunctiva simulating current clinical technique were well tolerated and demonstrated little change. Exposed implants produced obvious clinical inflammation and two of three exposed grafts disappeared during the 4- to 5-week interval. The single exposed implant that was retained demonstrated partial epithelialization but suffered extensive absorption and remodeling.

Animals↗
PubMed1979

Long-term effects of interval laparoscopic sterilization by bipolar electrocoagulation on menstruation.

We studied the menstrual patterns of 258 patients before and after laparoscopic sterilization by bipolar diathermy. The observed changes were obtained were mainly related to the kind of contraception used before sterilization. The frequency of menstrual disorders after sterilization were compared to those in a control group of non-sterilized women matched for age and parity: 12--42 months after the operation, the sterilized women did not have more irregular cycles, menorrhagia, metrorrhagia, hysmenorrhea or dyspareunia than the control group but the sterilized women did have a slightly higher incidence of polymenorrhea (p less than 0.05) and menses lasting less than 3 days (p less than 0.01). We conclude that interval laparoscopic sterilization by bipolar diathermy can be recommended for patients with normal menstrual cycles.

Adult↗
PubMed1978

[Possible late complications after peridural anaesthesia (author's transl)].

140 women who had received peridural anaesthesia (PDA) during childbirth at the University Gynaecological Hospital, Basel, in 1977, were retrospectively questioned on the occurrence of backache and headache during the puerperium subsequent to peridural anaesthesia. The "matched pairs" technique was employed for the controls. The inquiry revealed that in the PDA group 69 women (49%) and in the control group 39 women (28%) complained of increased backache during the puerperium. For 30 patients (44%) the complaints were a frequently disturbing factor in their everyday work. In the control group, this was true of 11 women (28%). 46 patients (33%) of the PDA group complained of increased headache during the puerperium, against 16 patients (11%) of the control group. 22 women (49%) of the PDA group felt disturbed in their daily work against 4 women (25%) among the controls. The findings are compared with data in literature, and the aetiology of the symptoms is discussed.

Anesthesia, Epidural↗