Dynamic tension spectroscopy and strength of biomembranes.
(33/240)
Rupturing fluid membrane vesicles with a steady ramp of micropipette suction produces a distribution of breakage tensions governed by the kinetic process of membrane failure. When plotted as a function of log(tension loading rate), the locations of distribution peaks define a dynamic tension spectrum with distinct regimes that reflect passage of prominent energy barriers along the kinetic pathway. Using tests on five types of giant phosphatidylcholine lipid vesicles over loading rates(tension/time) from 0.01-100 mN/m/s, we show that the kinetic process of membrane breakage can be modeled by a causal sequence of two thermally-activated transitions. At fast loading rates, a steep linear regime appears in each spectrum which implies that membrane failure starts with nucleation of a rare precursor defect. The slope and projected intercept of this regime are set by defect size and frequency of spontaneous formation, respectively. But at slow loading rates, each spectrum crosses over to a shallow-curved regime where rupture tension changes weakly with rate. This regime is predicted by the classical cavitation theory for opening an unstable hole in a two-dimensional film within the lifetime of the defect state. Under slow loading, membrane edge energy and the frequency scale for thermal fluctuations in hole size are the principal factors that govern the level of tension at failure. To critically test the model and obtain the parameters governing the rates of transition under stress, distributions of rupture tension were computed and matched to the measured histograms through solution of the kinetic master (Markov) equations for defect formation and annihilation or evolution to an unstable hole under a ramp of tension. As key predictors of membrane strength, the results for spontaneous frequencies of defect formation and hole edge energies were found to correlate with membrane thicknesses and elastic bending moduli, respectively. (+info)
Adhesively-tensed cell membranes: lysis kinetics and atomic force microscopy probing.
(34/240)
Membrane tension underlies a range of cell physiological processes. Strong adhesion of the simple red cell is used as a simple model of a spread cell with a finite membrane tension-a state which proves useful for studies of both membrane rupture kinetics and atomic force microscopy (AFM) probing of native structure. In agreement with theories of strong adhesion, the cell takes the form of a spherical cap on a substrate densely coated with poly-L-lysine. The spreading-induced tension, sigma, in the membrane is approximately 1 mN/m, which leads to rupture over many minutes; and sigma is estimated from comparable rupture times in separate micropipette aspiration experiments. Under the sharpened tip of an AFM probe, nano-Newton impingement forces (10-30 nN) are needed to penetrate the tensed erythrocyte membrane, and these forces increase exponentially with tip velocity ( approximately nm/ms). We use the results to clarify how tapping-mode AFM imaging works at high enough tip velocities to avoid rupturing the membrane while progressively compressing it to a approximately 20-nm steric core of lipid and protein. We also demonstrate novel, reproducible AFM imaging of tension-supported membranes in physiological buffer, and we describe a stable, distended network consistent with the spectrin cytoskeleton. Additionally, slow retraction of the AFM tip from the tensed membrane yields tether-extended, multipeak sawtooth patterns of average force approximately 200 pN. In sum we show how adhesive tensioning of the red cell can be used to gain novel insights into native membrane dynamics and structure. (+info)
The vacuum assisted closure of complex wounds: report of 3 cases.
(35/240)
Treatment of wounds using conventional methods is frequently limited by inadequate local wound conditions, or by a poor systemic clinical situation. Vacuum system may promote faster granulation tissue formation, remove excessive exudate, increase blood flow in the wound, and attract the borders of the wound to the center, reducing its dimension. We present 3 cases of patients with difficult wounds, due to bad local conditions, or poor clinical situation, in whom we used a vacuum system to prepare the wound for the surgical closure. One patient had a pressure ulcer, another had a diabetic foot ulcer, and the third one had an open foot stump. In the 3 cases a significant improvement of the wound conditions was achieved after 7 to 8 days, allowing successful surgical treatment with flap or skin grafts. (+info)
Decontamination of tried-in orthodontic molar bands.
(36/240)
Molar bands are commonly used to retain orthodontic attachments on posterior teeth and due to the variation in the size of such teeth, it is usually necessary to 'try in' several bands before the correct one is selected. A possible concern with re-using such bands is the lack of cross-infection control, even following autoclaving, due to the presence of one or more small bore lumen (the archwire and headgear tubes). The aim of this experiment was, therefore, to determine whether such bands could be successfully decontaminated so that they could be re-used without a cross-infection risk. Two hundred orthodontic molar bands that had previously been tried in patients' mouths, but not cemented into place, were tested. Each band was decontaminated using an enzymatic cleaner/disinfectant and then sterilized using either a downward displacement (n = 100) or a vacuum cycle autoclave (n = 100). Following autoclaving each band was inoculated into brain heart infusion culture broth and incubated at 37 degrees C for 5 days. None of the decontaminated bands exhibited growth after 5 days. It would appear that, using this methodology, there is little risk of a cross-infection hazard occurring with the re-use of previously tried-in and decontaminated molar bands. (+info)
Procedure-related complications of rapid amniodrainage in the treatment of polyhydramnios.
(37/240)
OBJECTIVE: To investigate the procedure-related complications of rapid amniodrainage in the treatment of polyhydramnios. METHODS: We followed prospectively all patients with polyhydramnios treated with rapid amniodrainage under continuous ultrasound guidance using a vacuum wound-drainage system from 1995 to 2002 in the fetal medicine unit of a university teaching hospital. We recorded: maternal age, type of pregnancy (singleton/twin), cause of polyhydramnios, gestational age at amniocentesis, volume of amniotic fluid drained, duration of the procedure, other intrauterine procedures in addition to the amniodrainage, and procedure-related complications including placental abruption, premature rupture of membranes (PROM), chorioamnionitis, fetal bradycardia and preterm delivery within 48 h of amniodrainage. RESULTS: Seventy-four consecutive women had 134 rapid amniodrainage procedures during the study period. Four procedures were excluded because the women were already in labor at the time of amniodrainage and they delivered within 48 h of the procedure. The final database therefore consisted of 70 patients with 130 procedures. Sixty-two percent (80/130) of the procedures were performed for the treatment of twin-twin transfusion syndrome (TTTS). There were altogether four procedure-related complications (3.1%; 95% CI, 1.0-8.0%). Three of them occurred in the TTTS group (3/80 procedures, 3.8%; 95% CI, 1.0-11.0%): one case each of placental abruption, PROM and fetal bradycardia. One PROM occurred in the non-TTTS group (1/50 procedures, 2.0%; 95% CI, 0-11.0%). In both cases of PROM the women presented in labor. CONCLUSIONS: Rapid amniodrainage using a vacuum wound-drainage system is safe and efficient to treat severe polyhydramnios, with a 3.1% complication rate. (+info)
Evaluation of Breast Imaging Reporting and Data System Category 3 mammograms and the use of stereotactic vacuum-assisted breast biopsy in a nonacademic community practice.
(38/240)
BACKGROUND: Breast Imaging Reporting and Data System (BI-RADS) Category 3 represents 'probably benign' mammographic abnormalities requiring close follow-up, but biopsies sometimes are performed on Category 3 abnormalities. Controversy exists as to when these biopsies are justified. The goals of the current study were to evaluate the use of stereotactic vacuum-assisted breast biopsy (SVABB) for BI-RADS 3 lesions in a nonacademic community hospital-based practice, to evaluate the false- negative rate of Category 3 mammograms, and to determine whether any specific lesions misinterpreted as BI-RADS 3 abnormalities might commonly be associated with malignant disease. METHODS: From August 2000 to December 2002, the authors performed 947 SVABB procedures on 911 patients. They focused on 156 SVABBs of BI-RADS 3 abnormalities. RESULTS: Of 634 SVABB procedures requested by outside sources, 114 (18%) were performed for BI-RADS 3 abnormalities, compared with 42 (13%) of 313 SVABB procedures that were performed based on mammographic findings at the authors' practice (P = 0.075). After SVABB, 7 of 156 patients with BI-RADS 3 lesions were diagnosed with breast carcinoma and 1 was diagnosed with atypical ductal hyperplasia. Therefore, the false-negative rate of BI-RADS 3 mammograms was 4.5% (i.e., 7 of 156 patients). Patients with linear microcalcifications had the highest rate of cancer (4 of 14 [29%]) compared with patients without microcalcifications (1 of 64 [1.5%]) and patients with nonlinear microcalcifications (2 of 69 [2.9%]). CONCLUSIONS: The use of SVABB for BI-RADS 3 lesions reflected uncertainty regarding the potential for a diagnosis of malignant disease rather than the financial incentive of performing a biopsy. SVABB was not necessary for patients with BI-RADS 3 lesions without microcalcifications or for patients with nonlinear microcalcifications. Lesions with linear (casting or branching) microcalcifications should not be considered BI-RADS 3 abnormalities. (+info)
Variation in palatability and biochemical traits within and among eleven beef muscles.
(39/240)
The objective of this study was to determine the extent of variation in, and relationships among, biochemical and palatability traits within and among 11 major beef muscles. Longissimus thoracis et lumborum (LD), psoas major (PM), gluteus medius (GM), semimembranosus (SM), adductor (AD), biceps femoris (BF), semitendinosus (ST), rectus femoris (RF), triceps brachii (TB), infraspinatus (IS), and supraspinatus (SS) from one side of 31 Charolais x MARC III steer carcasses were vacuum-packaged, stored at 2 degrees C until 14 d postmortem, and then frozen at -30 degrees C. The 2.54-cm-thick steaks were obtained from two or three locations within muscles in order to assess biochemical traits and Warner-Bratzler shear force, and from near the center for sensory trait evaluation. The PM was most tender and was followed by IS in both shear force and tenderness rating (P < 0.05). The other muscles were not ranked the same by shear force and tenderness rating. The BF had the lowest (P < 0.05) tenderness rating. The PM, GM, and LD had lower (P < 0.05) collagen concentration (2.7 to 4.5 mg/g muscle) than muscles from the chuck and round (5.9 to 9.0 mg/g), except for the AD (4.9 mg/g). Desmin proteolysis was highest (P < 0.05) for BF and LD (60.7 and 60.1% degraded), and was lowest (P < 0.05) for PM (20.2%). The PM, TB, IS, RF, and ST had relatively long sarcomere lengths (> 2.1 microm), whereas the GM had the shortest (P < 0.05) sarcomere length (1.7 microm). Cooking loss was lowest (P < 0.05) for BF (18.7%) and was followed by LD and IS (20.7%); it was highest (P < 0.05) for ST (27.4%). Across all muscles, tenderness rating was highly correlated (r > 0.60) with shear force, connective tissue rating, sarcomere length, and collagen content. Within a muscle, correlations among all traits were generally highest in LD and lowest in AD. Within muscle, location effects were detected (P < 0.05) for shear force (PM, ST, BF, SM, and RF), sarcomere length (PM, ST, BF, LD, SS, IS, SM, and RF), collagen concentration (PM, BF, SS, IS, SM. AD, TB, and RF), desmin degradation (PM, GM, BF, SM, AD, and, RF), and cooking loss (all muscles except SS and AD). There is a large amount of variation within and among muscles for tenderness traits and tenderness-related biochemical traits. These results increase our understanding of the sources of variation in tenderness in different muscles and provide a basis for the development of muscle-specific strategies for improving the quality and value of muscles. (+info)
Mammographic features and correlation with biopsy findings using 11-gauge stereotactic vacuum-assisted breast biopsy (SVABB).
(40/240)
BACKGROUND: Mammograms are assigned a BI-RADS (Breast Imaging Reporting and Data System) category, which indicates the level of suspicion for cancer. OBJECTIVES: (i) To evaluate the use of BI-RADS categories in a non-academic radiology practice based in a community hospital compared with local radiology private offices; (ii) to determine positive predictive value (PPV), sensitivity and specificity of mammograms; and (iii) to explore the correlation of BI-RAD 3-5 and lesion description with diagnosis of cancer. PATIENTS AND METHODS: We performed 947 SVABBs (stereotactic vacuum-assisted breast biopsies) on 911 patients with BI-RADS 3-5. Lesions were classified as: 1=microcalcifications; 2=asymmetric density; 3=circumscribed mass; and 4=spiculated mass. RESULTS: BI-RADS category correlated with diagnosis of breast cancer (atypia excluded): category 3=4%; category 4=15%; and category 5=79%. The PPV of BI-RADS 4 and 5 for breast cancer or atypia was 20%, in contrast to 5% for BI-RADS 3. Sensitivity and specificity were 95% and 19%, respectively. For BI-RADS 3 without microcalcifications only 3% were positive, in contrast to 8% for remainder. CONCLUSIONS: First, there is a stepwise increase in cancer for each of the BI-RADS categories 3-5. Secondly, in BI-RADS 3 with microcalcifications, a biopsy is indicated according to our findings. Finally, the sensitivity of mammograms is 95% but the specificity is 19%. (+info)