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Biomedical subjects

M Kon

Publications and source records attributed to M Kon.

At least 37 records · Page 2Linked to original sources
PubMed2000

Improving the preservation of isolated rat skeletal muscles stored for 16 hours at 4 degrees C.

BACKGROUND: Limiting factors for long-term cold preservation of isolated skeletal muscles are increased intracellular calcium levels, the occurrence of hypercontraction, and the overproduction of oxygen free radicals. In the present study, we investigated whether muscle preservation during cold storage could be improved by additives that can protect against such processes or by oxygen supply. METHODS: The soleus (SOL) and a strip of the cutaneus trunci muscle (CT) from the rat were isolated and stored for 16 hr at 4 degrees C in Bretschneider's Histidine Tryptophane Ketoglutarate (HTK) and subsequently acclimatized in Krebs-Henseleit solution for 90 min at room temperature. The protective effects of 2,3-butanedione monoxime (BDM; reduces intracellular calcium release and inhibits fiber contraction) and of the following antioxidants were investigated: N-tert-butyl-alpha-phenylnitrone (PBN), trolox, desferal, and deferione. The antioxidants and BDM were added to both HTK and Krebs-Henseleit solution. Dose-response curves were made for each of the additives (n> or =4 for each dose). To evaluate the effect of oxygen supply, HTK was aerated with 95% O2/5% CO2. Muscle function (P0), energy metabolism (ATP), and cytoarchitecture were analyzed. The measured values were compared with those of fresh unstored muscles (% of control) and with those of muscles stored in HTK without any additive (multivariate analysis of variance, P<0.05). RESULTS: We found a significant protection of the contractile function (P0) of both muscles after the addition of 1 mM of trolox (SOL: 46% of control; CT: 53%) and after the addition of 3 mM or 0.3 mM of deferione to the SOL and CT, respectively (P0 for both muscles: 55%), whereas no protection was found with PBN (0.03-1 mM) and Desferal (0.001-1 mM). The addition of BDM (10 or 30 mM) resulted in the highest increase of P0 (84% and 60% for the SOL and CT, respectively). The combinations BDM-trolox and BDM-deferione did not further improve the preservation of the SOL function, but P0 values (88% and 91% of control, respectively) were not different from those found for control muscles. Oxygenation of HTK was only beneficial for the SOL (P0: 83%). The improved preservation of muscle function was accompanied by a reduction of the twitch threshold current, increased by storage, suggesting a protective effect of the intervention on the preservation of the muscle cell membrane integrity. Biochemical and histological data corresponded well with the functional data. CONCLUSIONS: The results showed that the addition of BDM and antioxidants (trolox and deferione) to the bathing solutions improved the preservation of the function, metabolism, and cytoarchitecture of isolated skeletal muscles after cold storage for 16 hr.

Animals↗
PubMed2000

Effect of vascular freezing on the histopathology of dissected small vessels in the rat: vascular freezing does induce intimal hyperplasia in arteries and veins.

Intimal hyperplasia is the primary response of a vessel wall after injury. It may be the single most significant factor affecting long-term patency. The purpose of this study was to find out whether freeze injury, inflicted on rat microvessels, would be followed by intimal hyperplasia. Toward this aim, we exposed the superficial femoral vessels in the rat. On one side they were frozen using liquid nitrogen spray. The other side was dissected as the control. Vessel segments, harvested immediately and after 1, 2, 3, and 5 months, were studied light microscopically for the occurrence and content of intimal hyperplasia. In the arteries a considerable intimal hyperplasia was found within a 4-week interval, persisting for at least 5 months, as a result of the freeze injury. In the veins, the intimal hyperplasia was much less marked but was nevertheless demonstrable. These findings are not in agreement with earlier studies, in which freezing of injured rat microarteries with liquid nitrogen spray was followed by complete regeneration of the vessel wall, without intimal hyperplasia taking place. The factors contributing to these differences are discussed. It is concluded that freezing of a vessel wall is followed by intimal hyperplasia, which is part of the normal healing process.

Animals↗
PubMed2000

Strengthening of glass-ionomer cement by compounding short fibres with CaO-P2O5-SiO2-Al2O3 glass.

The purpose of this study was to determine if short fibres of CaO-P2O5-SiO2-Al2O3 (CPSA) glass possessing a particular aspect ratio (length/diameter) could be used as a reinforcing agent for glass-ionomer cement. The powder of a commercial glass-ionomer cement (not resin modified) was mixed with variously sized CPSA glass short fibres before mixing with the liquid of the glass-ionomer cement. The mixed powders containing 60 mass% CPSA glass short fibres (diameter, 9.7 +/- 2.1 microm, aspect ratio, 5.0 +/- 0.9) obtained maximum values of 18 and 35 MPa for the diametral tensile strength (DTS) and flexural strength (FS) of set cements, respectively, after 24 h. These DTS and FS values were 1.8 and 4.5 times larger, respectively, than those of the set glass-ionomer cement not containing short fibres. Moreover, it was found that the addition of CPSA glass short fibres was remarkably more effective in the strengthening than electric glass (a typical glass fibre) short fibres. The results suggested that the CPSA glass short fibres acted as a reinforcing agent for strengthening the glass-ionomer cement, because of the shape of short fibres and reactivity between the mixing liquid and short fibres.

Dental Cements↗
PubMed2000

Retrospective outcome analysis of staged flexor tendon reconstruction.

Forty staged flexor tendon reconstructions were done in 38 patients between 1991 and 1997. Results were assessed by clinical examination and questionnaire. At follow-up (mean, 35 months) a tenolysis had already been done in 12 cases. In the long fingers there was a significant difference between total active motion (187 degrees ) and total passive motion (237 degrees ). There was also a significant difference between active (24 degrees ) and passive (58 degrees ) IP motion in the thumbs. The mean power grip was 82%, pinch grip 74% and key grip 63% of the contralateral hand. None of the ten FPL reconstructions could be graded as excellent; four were good, using the criteria of Buck-Gramcko et al. (1976). Twenty-eight of the FDP reconstructions had excellent or good results. These results were better than the subjective scores given by the patients, 24 of whom complained of functional problems in daily life at follow-up.

Adolescent↗
PubMed2000

Sequential segmental neuromuscular stimulation reduces fatigue and improves perfusion in dynamic graciloplasty.

Dynamic graciloplasty is used as a treatment modality for total urinary incontinence caused by a paralyzed sphincter. A problem with this application is undesirable fatigue of the muscle caused by continuous electrical stimulation. Therefore, the neosphincter must be trained via a rigorous regimen to transform it from a fatigue-prone state to a fatigue-resistant state. To avoid or shorten this training period, the application of sequential segmental neuromuscular stimulation (SSNS) was examined. This form of stimulation proved previously to be highly effective in acutely reducing fatigue caused by electrical stimulation. The contractile function and perfusion of gracilis muscles employed as neosphincters were compared between conventional, single-channel, continuous stimulation, and multichannel sequential stimulation in 8 dogs. The sequentially stimulated neosphincter proved to have an endurance 2.9 times longer (as measured by halftime to fatigue) than continuous stimulation and a better blood perfusion during stimulation (both of which were significant changes, p < 0.05). Clinically, this will not antiquate training of the muscle, but SSNS could reduce the need for long and rigorous training protocols, making dynamic graciloplasty more attractive as a method of treating urinary or fecal incontinence.

Animals↗
PubMed2000

Use of the rectus abdominis muscle for abdominal stoma sphincter construction: an anatomical feasibility study.

Permanent fecal abdominal stomas significantly decrease quality of life. Previous attempts to create continent stomas by using dynamic myoplasty procedures have resulted in disappointing outcomes, primarily owing to denervation atrophy of the muscle flap that was used in the creation of the sphincter and because of muscle fatigue resulting from continuous electrical stimulation that is received by the flap to force contraction. On the basis of these problems, we designed two separate studies: an anatomical study addressing flap denervation and a functional study addressing muscle fatigue. The present study addresses the first topic and was designed to develop a rectus abdominis muscle flap into a sphincter that was anatomically situated to create a stoma while preserving as much innervation as possible. In 24 rectus abdominis muscles of human cadavers, the neurovascular anatomy was defined, then the anatomical feasibility of two different muscle flap configurations was considered. The flaps investigated were the peninsula flap and island flap designs, with both using the most caudal segment of the rectus abdominis muscle in construction of the sphincter. Neither flap design required the killing of a nerve for stoma sphincter creation, resulting in minimal muscle denervation. The conclusion of our comparison was that the above, in conjunction with other features of the island flap design, such as muscle overlap after sphincter formation and abdominal wall positioning of the sphincter, made the island flap design better suited to stoma sphincter construction.

Abdomen↗
PubMed2000

Sequential segmental neuromuscular stimulation: an effective approach to enhance fatigue resistance.

Electrical stimulation of skeletal muscle flaps is used clinically in applications that require contraction of muscle and force generation at the recipient site, for example, to assist a failing myocardium (cardiomyoplasty) or to reestablish urinary or fecal continence as a neo-sphincter (dynamic graciloplasty). A major problem in these applications (muscle fatigue) results from the nonphysiologic manner in which most of the fibers within the muscle are recruited in a single burst-like contraction. To circumvent this problem, current protocols call for the muscle to be put through a rigorous training regimen to transform it from a fatigue-prone to a fatigue-resistant state. This process takes several weeks during which, aside from becoming fatigue-resistant, the muscle loses power and contraction speed. This study tested the feasibility of electrically stimulating a muscle flap in a more physiologic way; namely, by stimulating different anatomical parts of the muscle sequentially rather than the entire muscle all at once. Sequential segmental neuromuscular stimulation (SSNS) allows parts of the muscle to rest while other parts are contracting. In a paired designed study in dogs (n = 7), the effects of SSNS on muscle fatigability and muscle blood perfusion in gracilis muscles were compared with conventional stimulation: SSNS on one side and whole muscle stimulation on the other. In SSNS, electrodes were implanted in the muscles in such a way that four separate segments of each muscle could be stimulated separately. Then, each segment was stimulated so that part of the muscle was always contracted while part was always resting. This type of stimulation permitted sequential yet continuous force generation. Muscles in both groups maintained an equal amount of continuous force. In SSNS muscles, separate segments were stimulated so that the duty cycle for any one segment was 25, 50, 75, or 100 percent, thus varying the amount of work and rest that any segment experienced at any one time. With duty cycles of 25, 50, and 75 percent, SSNS produced significantly (p < 0.01) enhanced resistance to fatigue. In addition, muscle perfusion was significantly (p < 0.01) increased in these sequentially stimulated muscles compared with the controls receiving whole muscle stimulation. It was concluded that SSNS reduces muscle fatigue and enhances muscle blood flow during stimulation. These findings suggest that using SSNS in clinical myoplasty procedures could obviate the need for prolonged training protocols and minimize problems associated with muscle training.

Animals↗
PubMed2000

Pressure-induced skin lesions in pigs: reperfusion injury and the effects of vitamin E.

The pathogenesis of the development of pressure ulcers is still unclear. The aim of this study was to investigate the role of ischaemia and reperfusion in pressure-induced tissue necrosis in the trochanteric region in pigs. Pressure application was achieved with a newly developed computer-controlled pressure device. Histological examination showed damage in the subcutis and muscle tissue comparable with inflammation, extending in a vascular pattern beyond the area of pressure application. Electron-microscopic studies revealed neutrophil adherence to the capillary endothelium, which showed signs of injury. These observations were manifest two hours after the cessation of pressure. Pre-treatment with 500 mg vitamin E per day resulted in significantly less tissue damage compared with untreated animals. Pressure alone caused a significant decrease in reduced glutathione and total glutathione, suggesting oxidative stress. After pressure release there was a significant increase in hydrogen peroxide concentration, suggesting a decreased antioxidant protection. After pre-treatment with vitamin E, however, there was no increase of hydrogen peroxide. It is concluded that the early signs of necrosis after pressure application are concordant with typical ischaemia-reperfusion damage and this can be prevented in part by treatment with vitamin E. Prophylactic administration of vitamin E may influence the occurrence of pressure ulcers in humans undergoing elective surgery.

Animals↗
PubMed1999

Right ventricular function after pulmonary autograft replacement of the aortic valve.

BACKGROUND: The pulmonary autograft operation (the Ross procedure) involves excision of a portion of the right ventricular (RV) outflow tract, prolonged cross-clamp times, and insertion of a pulmonary homograft. There is concern about the effect of such operations on right ventricular function. METHODS AND RESULTS: Twenty-five patients undergoing either pulmonary autograft or homograft replacement of the aortic valve as part of a prospective randomized trial had echocardiographic RV long-axis measurements performed before surgery and 6 months (range 3 to 12 months) after surgery. In all patients, systolic excursion (SE) and both shortening and lengthening rates (SR and LR, respectively) were reduced postoperatively (P<0.05) (homografts: SE 1.5+/-0.4 versus 2.3+/-0.6 cm, SR 6.8+/-2.1 versus 9. 6+/-3.1 cm/s, LR 6.0+/-1.8 versus 8.9+/-3.0 cm/s; autografts: SE 1. 4+/-0.4 versus 2.2+/-0.4 cm, SR 5.8+/-3.0 versus 8.2+/-3.0 cm/s, LR 5.7+/-1.9 versus 8.5+/-3.7 cm/s). There were no differences between the 2 groups. Eighteen patients who had undergone either aortic homograft or pulmonary autograft surgery were studied between 6 and 35 months after surgery. RV volumes were assessed with the use of MRI in addition to echocardiographic RV long-axis measurements. Global volumes were increased to a similar amount in both groups (homografts: end-diastolic volume 145+/-34 mL, end-systolic volume 78+/-23 mL; autografts: end-diastolic volume 157+/-33 mL, end-systolic volume 89+/-25 mL; P=NS), whereas stroke volumes were maintained in both groups (homografts 67+/-15 mL, autografts 67+/-16 mL; P=NS). RV SE was depressed in both groups to a similar degree to that seen with the previous group (homografts 1.5+/-0.3 cm, autografts 1.4+/-0.2 cm). CONCLUSIONS: Aortic valve replacement with either a pulmonary autograft or an aortic homograft leads to a degree of persistent RV longitudinal dysfunction that is not more pronounced in those undergoing the Ross procedure. The mechanisms and long-term effects of these changes must be further studied.

Adolescent↗
PubMed1999

[Free muscle transplantation after complex fractures of the lower leg and ankle: results from 32 patients].

OBJECTIVE: To describe the results of free vascularized muscle transfer for treatment of complications of severe open fractures of the distal tibia and ankle region. DESIGN: Retrospective. METHODS: In 1994-1998, 32 patients underwent free muscle transfer for soft tissue reconstruction after high energy injury to the distal tibia and ankle region. In six patients reconstruction took place within one week after the injury (group 1); 13 patients underwent free muscle transfer in combination with (re)osteosynthesis and cancellous bone grafting for treatment of infected (defect) pseudarthrosis (group 2); chronic posttraumatic osteitis existed for an average of 12 years in six patients (group 3); in seven patients the indication was determined by unstable scar tissue, cosmetic reasons, or as preparation for corrective osteotomy (group 4). RESULTS: Three haematomas and two thrombembolic complications were encountered. Amputation could not be avoided in three patients. Consolidation of the fracture, pseudarthrosis or arthrodesis and/or eradication of infection was accomplished in all remaining 29 patients. An average of 2.2 (range: 0-7) reinterventions were additionally needed in groups 1-3, including reosteosynthesis, sequestrectomy, cancellous bone grafting and/or arthrodesis. CONCLUSION: In case of severe open fracture of the distal tibia and/or ankle region, free vascularized muscle transfer provided cover of the fracture or pseudarthrosis region, thereby improving local vascularisation. This treatment protects the underlying bone, enhances osteogenesis and improves resistance to infection.

Adult↗
PubMed1999

Microcirculatory changes following different temperature washouts in a free flap model.

In spite of the extensive experimental work on vascular washout in free flap surgery, an optimal temperature for the washout solution has not been established. This study was designed to determine the effect of the washout solution temperature on the degree to which the microcirculation is cleared of blood. The cremaster muscle flap in the rat was used, in which the microcirculation can be directly viewed and the presence of blood and perfusion parameters within various vessels can be measured during and after washout. Washout was started with a single, high-pressure infusion and continued at 130 mmHg for 15 minutes. The temperature of the washout solution was either 2-3, 20-22, or 35 degrees C. In all three groups, washout cleared the microcirculation almost completely within the first minute. However, we observed that a cold or room temperature washout cleared the microcirculation more completely than a warm washout did. The temperature of the washout solution did not effect post washout capillary perfusion and/or arterial diameters.

Animals↗
PubMed1999

Contractile properties of rat skeletal muscles following storage at 4 degrees C.

The purpose of this study was to assess the potential of preservation solutions for protecting skeletal muscle function during storage at 4 degrees C. The soleus and the cutaneus trunci (CT) from the rat were stored for 2, 8 or 16 h at 4 degrees C in University of Wisconsin solution (UW), HTK-Bretschneider solution (HTK) or Krebs-Henseleit solution (KH). After storage, muscles were stimulated electrically to analyse the isometric contractile properties, such as the maximum tetanic tension (P(0)). Histological analysis was also performed. In separate experiments, the effect of the diffusion distance on muscle preservation was studied by bisecting the soleus. After 8 h of storage in UW or HTK, the contractile properties of the CT were similar to those of the control, whereas those of the soleus were reduced (P(0) values of 16% and 69% of control in UW and HTK respectively). At 16 h, the contractile properties of the CT (P(O) 28%) were again better preserved than those of the soleus (P(0) 9%). Muscle function deteriorated most after storage in KH (P(0) at 16 h: soleus, 3%; CT, 17%). The bisected soleus was equally well preserved as the CT (P(O) of bisected soleus at 8 h in UW and HTK: 86%). The functional data corresponded well with the histological data, which showed increasing muscle fibre derangement with increasing storage time. For both muscles and all solutions, the threshold stimulus current increased with increasing storage time (control, 0.1 mA; 16 h, 1.2 mA) and was strongly correlated with the deterioration in contractile properties. It is concluded that, at 4 degrees C, muscle is preserved better in UW and HTK (intracellular-like solutions) than in KH (extracellular-like solution). The soleus and CT were best protected in HTK. The diffusion distance is a critical factor for successful preservation of muscle function at 4 degrees C. The reduced function after 16 h of storage at 4 degrees C was caused by hypercontraction and necrosis of about 25% of the muscle fibres, and by deterioration of the electrical component of excitation-contraction coupling of the remaining fibres.

Animals↗
PubMed1999

Three parameters optimizing closed-loop control in sequential segmental neuromuscular stimulation.

In conventional dynamic myoplasties, the force generation is poorly controlled. This causes unnecessary fatigue of the transposed/transplanted electrically stimulated muscles and causes damage to the involved tissues. We introduced sequential segmental neuromuscular stimulation (SSNS) to reduce muscle fatigue by allowing part of the muscle to rest periodically while the other parts work. Despite this improvement, we hypothesize that fatigue could be further reduced in some applications of dynamic myoplasty if the muscles were made to contract according to need. The first necessary step is to gain appropriate control over the contractile activity of the dynamic myoplasty. Therefore, closed-loop control was tested on a sequentially stimulated neosphincter to strive for the best possible control over the amount of generated pressure. A selection of parameters was validated for optimizing control. We concluded that the frequency of corrections, the threshold for corrections, and the transition time are meaningful parameters in the controlling algorithm of the closed-loop control in a sequentially stimulated myoplasty.

Algorithms↗
PubMed1999

Fracture toughness and durability of chemically or thermally tempered metal-ceramic porcelain.

Thermocycling and water storage effects on fracture toughness (KIC) of chemically or thermally tempered metal-ceramic disks were investigated to evaluate the durability of tempering effects with regard to oral aqueous environment. Metal-ceramic disks (phi 10 mm x 2.0 mm) consisting of opaque porcelain (0.2 mm thick), body porcelain (1.3 mm) and Ni-Cr-Be alloy (0.5 mm) were prepared and the porcelain surfaces were polished with 1-micron diamond paste. The disks were subjected to ion exchange (potassium or rubidium) or thermal tempering treatments, then with the as-polished or further annealed disks, thermocycled for 8000, 15,000, and 22,000 cycles between 5 degrees C and 60 degrees C or stored in water at 37 degrees C for 33 days. After aging, KIC values of disks were determined by a Vickers indentation technique. Statistical analyses indicated that the KIC values of ion-exchanged and annealed disks were not significantly affected by the limited number of cycles and water storage, while the thermally tempered and untreated disks revealed a significant decrease in mean KIC from even 8000 cycles and after storage. However, there was no significant difference between thermocycling and water-storage effects on mean KIC of all surface treatment groups. Results indicate that chemical tempering (ion exchange) produced more durable residual stresses than does thermal tempering for metal-ceramic restorations. A low-thermal load only was unlikely to affect the apparent fracture toughness of porcelain.

Chromium Alloys↗
PubMed1998

[Liposuction].

Liposuction is a frequently applied technique in aesthetic plastic surgery, with which subcutaneous adipose tissue can be removed. In recent decades new techniques of liposuction were developed. This led to better results and fewer complications. Liposuction is indicated as symptomatic treatment of obesity and (or) lipomas. Liposuction is not without risks; patients have to be informed of practical consequences and possible complications of the technique.

Adiposis Dolorosa↗
PubMed1998

Effects of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement.

The effect of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement (aw-FSCPC) was investigated in a preliminary evaluation of aw-FSCPC containing drugs. Flomoxef sodium was employed as the antibiotic and was incorporated into the powder-phase aw-FSCPC at up to 10%. The setting time, consistency, wet diametral tensile strength (DTS) value, and porosity were measured for aw-FSCPC containing various amounts of flomoxef sodium. X-ray diffraction (XRD) analysis was also conducted for the identification of products. To evaluate the drug-release profile, set aw-FSCPC was immersed in saline and the released flomoxef sodium was determined at regular intervals. The spread area of the cement paste as an index of consistency of the cement increased progressively with the addition of flomoxef sodium, and it doubled when the aw-FSCPC contained 8% flomoxef sodium. In contrast, the wet DTS value decreased with increase in flomoxef sodium content. Bulk density measurement and scanning electron microscopic observation revealed that the set mass was more porous with the amount of flomoxef sodium contained in the aw-FSCPC. The XRD analysis revealed that formation of hydroxyapatite (HAP) from aw-FSCPC was reduced even after 24 h, when the aw-FSCPC contained flomoxef sodium at > or = 6%. Therefore, the decrease of wet DTS value was thought to be partly the result of the increased porosity and inhibition of HAP formation in aw-FSCPC containing large amounts of flomoxef sodium. The flomoxef sodium release from aw-FSCPC showed the typical profile observed in a skeleton-type drug delivery system (DDS). The rate of drug release from aw-FSCPC can be controlled by changing the concentration of sodium alginate. Although flomoxef sodium addition has certain disadvantageous effects on the basic properties of aw-FSCPC, we conclude that aw-FSCPC is a good candidate for potential use as a DDS carrier that may be useful in surgical operations.

Biocompatible Materials↗