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Biomedical subjects

X Deng

Publications and source records attributed to X Deng.

198 records · Page 11Linked to original sources
PubMedDate not supplied

Gas chromatographic--mass spectrometric determination of etomidate in mouse brain.

A simple, rapid and reliable method was developed to determine the concentration of etomidate [ethyl-1-(1-phenylethyl)-1 H-imidazole-5-carboxylate] in mouse brain tissue by gas chromatography-mass spectrometry (GC-MS). Ethyl 5-amino-1-phenyl-4-pyrazolecarboxylate was used as internal standard (IS) and liquid-liquid extraction using ethyl ether as the solvent. The method demonstrated excellent recovery (93%) and a linear calibration range of 50-2500 ng/0.2 g. Intra-day accuracy and precision had an error and coefficient of variation of less than 8.7% and 4.2%, respectively. The limit of detection was 1 ng in mouse brain. Our results suggest that this new method is suitable for the quantitative analysis of etomidate in mouse brain tissue.

Anesthetics, Intravenous↗
PubMedDate not supplied

Dissociation of modular humeral head components: a biomechanical and implant retrieval study.

In vivo dissociation of the Morse-taper of shoulder arthroplasty modular humeral components has been reported. The incidence of this complication appears to be approximately 1:1000. The objective of this study was to identify conditions that might affect the Morse-taper interface strength in humeral components. Mechanical tests were performed to load and dissociate humeral heads from the humeral stems (titanium). The effect of loading rate, load amplitude, and number of impactions was investigated. Dissociation force was measured after the taper was contaminated with water, oil, blood, and bone cement particles. The mean dissociation force after two impactions with a mallet was 2926 +/- 955 N. Dissociation force was linearly proportional to impaction force. Repetitive loading beyond two impactions did not significantly increase taper strength. Contamination of the taper with as little as 0.4 ml of fluid could prevent fixation of the taper.

Biomechanical Phenomena↗
PubMedDate not supplied

Effect of joint compression on inferior stability of the glenohumeral joint.

UNLABELLED: To determine the relative importance of negative intraarticular pressure, capsular tension, and joint compression on inferior stability of the glenohumeral joint we studied 17 fresh, normal adult cadaver shoulders using a "3 degrees of freedom" shoulder test apparatus. Translations were measured in intact and vented shoulders while a 50-N superior and inferior directed force was applied to the shoulder. Three different joint compressive loads (22 N, 111 N, 222 N) were applied externally. Tests were performed in 3 positions of humeral abduction in the scapular plane (0 degree, 45 degrees, 90 degrees) and in 3 positions of rotation (neutral, maximal internal, and maximal external). After tests of the intact and vented shoulder, the glenohumeral ligaments were sectioned and tests were repeated. With minimal joint compression of 22 N, negative intraarticular pressure and capsular tension limited translation of the humeral head on the glenoid. Increasing the joint compressive load to 111 N resulted in a reduction of mean inferior translation from 11.0 mm to 2.0 mm at 0 degree abduction, from 21.5 mm to 1.4 mm at 45 degrees abduction, and from 4.5 mm to 1.2 mm at 90 degrees abduction. With a compressive load of 111 N, venting the capsule or sectioning of glenohumeral ligaments had no effect on inferior stability. CLINICAL RELEVANCE: Glenohumeral joint compression through muscle contraction provides stability against inferior translation of the humeral head, and this effect is more important than negative intraarticular pressure or ligament tension.

Adult↗
PubMedDate not supplied

Localization of atherosclerosis in arterial junctions. Concentration distribution of low density lipoproteins at the luminal surface in regions of disturbed flow.

To investigate the role of fluid mechanical factors in atherogenesis and anastomotic intimal hyperplasia, the effect of blood flow on the transfer of low density lipoproteins from flowing blood to the luminal surface was studied theoretically using a two dimensional T-junction model. The flow fields in the junction were obtained by solving the Navier-Stokes equations numerically and the concentration distribution of low density lipoproteins at the luminal surface was determined using a finite difference analysis. The transfer of low density lipoproteins from flowing blood to the surface of the vessel wall was greatly enhanced in the two regions of disturbed flow, one in the main vessel, the other in the subsidiary vessel. The highest concentration of low density lipoproteins on the inner surface of the vessel wall was predicted to occur in the areas of the reattachment points. The slower the recirculation flow, the higher the lipid accumulation at the luminal surface in the disturbed flow regions and the wider the highly concentrated low density lipoprotein area. In summary, the authors' mathematical model predicts that locally disturbed blood flows at arterial bifurcations and surgically created junctions provide favorable conditions for the accumulation of atherogenic substances at the luminal surface, thus increasing the potential for lipid infiltration into the vessel wall.

Anastomosis, Surgical↗
PubMedDate not supplied

Can collagen impregnated polyester arterial prostheses be recommended as small diameter blood conduits?

A collagen impregnated graft and its parent preclotted prosthesis were implanted as thoraco-abdominal bypasses in dogs for periods ranging from 4 hr to 6 months and evaluated for their ease of handling, imperviousness, and healing behavior in terms of luminal surface thrombogenicity using labeled platelets and fibrinogen, prostacyclin (PGI2) secretion, histomorphometric determination of internal capsule thickness, and histopathologic and scanning electron microscopic studies. The collagen impregnated graft was impervious to blood and both grafts showed excellent handling characteristics. Fibrin uptake was negligible on both grafts; however, platelet uptake was higher on the collagen impregnated graft than on the control graft at 4 and 24 hr. The healing behavior of the collagen impregnated graft was also found to be different than that of the control graft between 1 and 6 months post implantation. The development of a host collagenous internal capsule at the anastomoses, and a confluent endothelial lining, was observed in both grafts at 1 month; in later implantation periods, the healing of the medial region was found to be more irregular in the collagen impregnated grafts, showing a lower mean PGI2 secretion than the preclotted control grafts. Histomorphometric analysis showed the internal capsule on the collagen impregnated grafts to be thicker than on the control grafts for most periods of implantation. The current study illustrates that the healing process of collagen impregnated grafts is delayed and that bovine collagen has a stimulating effect on tissue encapsulation. Current impregnated polyester arterial prostheses therefore cannot be recommended as small diameter blood conduits.

Animals↗
PubMedDate not supplied

Polyester arterial prostheses. Recent developments from the Czech Republic and Poland.

To evaluate recent developments in the design and production of polyester vascular prostheses in eastern Europe, a series of in vitro physical and chemical tests and an in vivo study was performed on three new prototype devices from the Czech Republic and one from Poland. The in vitro results for these four prostheses, referred to as the Ra-1n (warp knitted, uncrimped), Ra-1v (warp knitted, crimped), Mikrofroté (weft knitted, uncrimped), and Dallon (warp knitted, crimped) prostheses, were compared against values for three commercial devices of western origin, namely the Triaxial, the Vasculour II, and the Cooley II grafts. The animal trial involved implanting the four prototype devices as a thoracoabdominal bypass in dogs for eight different periods ranging from 4 hrs to 6 months and undertaking histologic and structural investigations on the retrieved grafts. Because of its poor long-term dimensional stability in vivo, the continued use of a weft knitted structure, like the Mikrofroté prosthesis, is to be deprecated. Conversely, the introduction of a more dimensionally stable warp knitted structure in three prototypes is to be acknowledged. However, the presence of surface contaminants was most likely responsible for the excessive inflammatory reaction generated by all four prostheses during the first month in vivo, which resulted in delayed healing performance. In addition, an unusually high surface carbon-oxygen ratio suggests that the crimping process needs further refinement. Improved cleaning and packaging procedures are essential before these products can complete against existing commercial prostheses of western origin. In conclusion, these new developments illustrate that the technology of warp knitting, which is now spreading worldwide, should be evaluated.

Animals↗
PubMedDate not supplied

A capillary method to measure water transmission through polyurethane membranes.

A capillary method has been developed to measure the rate of water transmission through polyurethane membranes prepared for use as ventricles in artificial hearts. The system consisted primarily of a leak-proof sample chamber containing the water, a glass capillary flow meter, and a receiver compartment with continuous dry air ventilation. The capillary flow meter monitored the volume of water loss in the sample chamber. The rate of water transmission through the test membrane was found to be proportional to the water loss in the sample chamber, and dependent on the membrane thickness. For thicknesses from 0.09 mm to 0.34 mm, water vapor transmission rates ranged from 7.53 x 10(-8) to 2.76 x 10(-8) mol/s cm2, respectively. Although the concentration of water vapor in the receiver compartment did affect the rate of water vapor transmission through the membrane, within the pressure range 50-200 mmHg, there was very little effect. These findings suggest that water transmission through a polyurethane membrane is dominated by a diffusion process rather than by bulk convection.

Biocompatible Materials↗
PubMedDate not supplied

Theoretical prediction of the hemodynamic performance of slow resorbing polyester protein impregnated arterial prostheses after implantation: a plea for fast resorption of the coating.

The clinical literature cites cases where slow, incomplete, or nonuniform protein resorption from protein impregnated arterial prostheses produces undesirable localized internal capsule proliferation leading to a significant reduction of the internal diameter of the prosthesis. In an attempt to describe the hemodynamic response to this phenomenon, the blood flow in such stenotic regions was simulated and characterized numerically using FIDAP computational fluid dynamics software to determine the Navier-Stokes and continuity equations for simple channel flow. To simulate various stages of internal capsule development, numeric computations were made in an idealized tubular expansion at stenosis ratios ranging from 0.9 to 0.5 and stenosis length ratios from 10 to 40. The results indicated that a triangular annular ring vortex was formed immediately distal to the stenosis at all Reynolds numbers (Re) studied. The size of the vortex increased almost linearly with the Reynolds number. The pressure drop through the stenosis was affected by blood flow rate, severity, and stenosis length. When the stenosis ratio was low, the pressure drop through the stenosis increased gradually and almost linearly with blood flow rate. In a severe stenosis, the pressure drop was no longer a linear function of flow rate, but increased significantly with increasing flow rate. In conclusion, satisfactory healing of the internal capsule requires fast resorption of any impregnated protein. If the resorption is slow, incomplete, or nonuniform, there is a tendency for the lumen to narrow, causing stenosis, an increased pressure drop through the narrowed graft and disturbed flow distal to the stenosis. This phenomenon therefore constitutes a major limitation for using this type of graft in small diameter arterial reconstruction.

Absorbable Implants↗
PubMedDate not supplied

The effect of joint-compressive load and quadriceps muscle force on knee motion in the intact and anterior cruciate ligament-sectioned knee.

To determine the effect of an externally applied joint-compressive load and a quadriceps muscle force on knee motion, we tested nine intact cadaveric knees and four knees after sectioning of the anterior cruciate ligament. Anteroposterior translation was measured at 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 90 degrees of knee flexion after the application of an anteroposterior force of 100 N, a joint-compressive load of 0, 111, 222, 333, or 444 N, and a quadriceps force of 0 or 133 N. Both a joint-compressive load and a quadriceps force significantly decreased total anteroposterior translation by as much as 50% to 66% in intact knees and 42% to 71% in anterior cruciate ligament-sectioned knees. A substantial anterior translation was also found with the application of a joint-compressive load or a quadriceps force and no anterior force. We termed this translation an anterior neutral-position shift. The anterior neutral-position shift was significantly greater in the ligament-sectioned knees compared with the intact knees, so much so that at flexion angles greater than 15 degrees, the application of a 100-N posterior force could not translate the tibia to the most anterior position achieved in the intact knee with a 100-N anterior force.

Aged↗
PubMedDate not supplied

Strategies for an anterior capsular shift of the shoulder. A biomechanical comparison.

We evaluated the effect of two different anterior capsular shift strategies on load-induced multidirectional glenohumeral motion. Nine cadaveric shoulders were tested on a special test apparatus in which three motions were constrained but which allowed simultaneous measurement of three translations: anteroposterior, mediolateral, and superoinferior. A simulated Bankart lesion was created by detaching the inferior glenohumeral ligament and labrum from the anterior glenoid from 5 mm superior to the anterior band of the inferior glenohumeral ligament to a point just posterior to the infraglenoid tubercle. The two types of medial-based anterior capsular shifts were performed sequentially using fixation via a transglenoid drill hole and No. 2 suture. One shift medialized the anterior capsule on the glenoid by 5 mm; the other one shifted the anterior capsule 5 mm superior on the anterior glenoid. Biomechanical testing was done in two positions of humeral elevation in the scapular plane, three positions of humeral rotation, and with an externally applied joint compression load of 22 N. Glenohumeral motion was measured in the intact state, after creation of the simulated Bankart lesion, and after each of the two anterior capsular shifts. Both the superior and medial shifts of the capsule decreased anterior glenohumeral translation to equivalent extents. For posterior and inferior translation at 45 degrees elevation, the superior shift significantly decreased translation to a greater extent than did the medial shift.

Aged↗
PubMedDate not supplied

The popliteofibular ligament. Rediscovery of a key element in posterolateral stability.

We have recently become aware of a strong direct attachment of the popliteal tendon to the fibula. To investigate the importance of this attachment, we examined 20 cadaveric knees. The popliteofibular ligament was identified in all 20 knees. The cross-sectional area of the popliteofibular ligament was 6.9 +/- 2.1 mm2, compared with 7.2 +/- 2.7 mm2 for the lateral collateral ligament. Biomechanical testing of these structures, simulating a purely varus stress on the knee, revealed that the lateral collateral ligament always failed first, followed by the popliteofibular ligament, and then the muscle belly of the popliteus. The mean maximal force to failure of the popliteofibular ligament approached 425 N (range, 204 to 778), compared with 750 N (range, 317 to 1203) for the lateral collateral ligament. Our results indicate that the popliteofibular ligament contributes to posterolateral stability.

Adult↗
PubMedDate not supplied

Longitudinal forces acting on a knitted polyester arterial prosthesis when implanted as a thoracic aorta substitute in the dog.

The longitudinal forces under which arterial prostheses are held in situ are of great importance. The tension caused by the longitudinal force may be one of the factors involved in the formation of anastomotic false aneurysms. In order to measure the changes in the longitudinal force at both proximal and distal end-to-end anastomoses over different periods of implantation, we devised an experimental study in which the changes in length of a warp-knitted polyester VP1200K (Vascutek Ltd., Inchinnan, Scotland) arterial prosthesis, used as a thoracic aorta substitute in the dog, were recorded photographically at implantation and removal. The longitudinal forces acting at the two sites were then calculated using a linear relationship between the longitudinal force and the changes in length of a virgin prosthesis, which was found experimentally in vitro using a computerized laser calibration system. One-tailed Student's t-test showed no significant difference between the length indicator values at the two anastomotic sites at different periods of implantation except during the 1-month period. Textile analysis of the explanted prostheses and histopathologic observations confirmed this similar behavior at the two anastomotic sites. These observations were contrary to the theoretic prediction regarding the effect of forces applied by drag and tissue ingrowth. Nevertheless, analysis of variance confirmed that there was no difference evident at the two sites between different implantation periods. These observations may explain why the formation of anastomotic false aneurysms is less common at end-to-end anastomoses.

Animals↗
PubMedDate not supplied

Longitudinal forces acting at side-to-end and end-to-side anastomoses when a knitted polyester arterial prosthesis is implanted in the dog.

In a previous study, which investigated the tensions at the proximal and distal end-to-end anastomoses of a vascular prosthesis, no significant differences were found in the longitudinal forces between the two anastomotic sites after different periods of implantation. The present follow-up study was devised to study the longitudinal forces at a proximal side-to-end and a distal end-to-side anastomosis using a warp knitted polyester prosthesis implanted as a canine thorocoabdominal bypass. The external surface of the prosthesis contained a specially printed "tension indicator" design, which enabled changes in length to be assessed photographically at the two anastomoses at the time of implantation and at sacrifice. The longitudinal force at each site was then calculated using a relationship obtained experimentally between the total longitudinal force and the changes in length of the virgin graft in vitro. The in vitro measurements on the prosthesis were performed using a computer-controlled laser calibration system. Although the results showed a tendency toward a gradual loss in longitudinal force at both anastomoses over 7 months in situ, statistical analysis showed no significant difference in the longitudinal force at the two anastomotic sites after any period of implantation. Histopathological and textile analysis also showed that the characteristics of the prostheses were similar at both anastomotic sites. This does not mean, however, that the intramural stress concentrations experienced by the two sites were the same. While comparing the level of the longitudinal forces measured in this study with those observed in the previous thoracic aorta study using end-to-end anastomoses, no significant differences were observed due to the different types of anastomoses. It would appear that the longitudinal force is not one of the main etiological factors that cause the formation and localization of anastomotic failure.

Anastomosis, Surgical↗
PubMedDate not supplied

Influence of anti-inflammatory and antioxidant agents on endothelial permeability alterations induced by bradykinin.

Increased vascular permeability to plasma proteins and altered hemodynamics at the site of inflammation are characteristics of inflammation. In the present study, alterations in endothelial barrier permeability were evaluated in different organs/tissues 6 h after a systemic inflammatory response induced by intravenous injection of bradykinin (BK; 1.7 mg/kg). The effect of intravenous pretreatment with indomethacin or ibuprofen (cyclooxygenase inhibitors), N-acetyl-L-cysteine (NAC, an oxygen free radical scavenger), and allopurinol (a xanthine oxidase inhibitor) was determined. Endothelial permeability was evaluated by determining tissue water content (TWC), 125I-labeled human serum albumin (HSA) flux, and albumin leakage index (ALI) in various organs/tissues. The vasodilation in the local tissues was reflected by tissue blood content (TBC), measured by 51Cr-labeled red blood cells. The results indicate that albumin flux significantly increased in the peritoneum, pancreas, stomach, PSI, DSI, colon, kidneys, liver, lungs, and brain, TBC significantly increased in the kidneys, liver, lungs, and heart, as well as in the intestine, and an increased ALI, assaying endothelial permeability considering local hemodynamic alterations was noted in the pancreas, kidneys, liver, lungs, PSI, and DSI in the group with BK alone. These changes were to varying degrees reversed by pretreatment with indomethacin, ibuprofen, N-acetyl-L-cysteine, or allopurinol, where the protective effect tended to be organ-dependent.

Acetylcysteine↗
PubMedDate not supplied

Mouse Spam1 (PH-20): evidence for its expression in the epididymis and for a new category of spermatogenic-expressed genes.

The gene for the sperm adhesion molecule 1 (PH-20), SPAM1, has been known to be testis-specific and exclusively haploid expressed. We show that in mice, the 2 common isoforms of the protein (Spam1) observed in sperm are also present in the caput, corpus, and cauda epididymides. Both qualitative and quantitative variation of expression of the protein were observed in epididymis with the highest expression detected in the corpus. The endogenous production of enzymatically active (via hyaluronidase) Spam1 by epididymal cells is supported by the detection of steady-state Spam1 epididymal messenger RNA in both wild type and germ cell-deficient mice. In situ transcript hybridization shows the transcript to be localized to the principal cells of the epithelium. The protein was similarly immunolocalized to these cells, predominantly in vesicles near the apical region. The results suggest a mechanism for transportation of Spam1 from the epididymal epithelium to sperm during their transit and storage in the cauda. None of the current categories of spermatogenic-expressed genes shows the dual transcription pattern (haploid testicular/diploid epididymal) observed for Spam1. The work also confirms and extends the finding that Spam1 is expressed in the kidney.

Animals↗
PubMedDate not supplied

Uptake of 3H-7-cholesterol along the arterial wall at an area of stenosis.

Abnormal uptake of atherogenic substances and lipid infiltration have been believed to contribute to the localized genesis and development of atherosclerosis, as well as to late failures of synthetic arterial prostheses. To verify the theoretical prediction that accumulation of lipoproteins on the luminal surface of arterial walls occurs in the regions of disturbed flow, we have carried out an in vitro mass transfer experiment to test the effect of a pseudo steady recirculation flow on the uptake of 3H-7-cholesterol by the arterial wall at a surgically created stenosis. It was found that, as predicted by the theory, in the flow field of the stenosis the uptake of labeled cholesterol reached a maximum around the reattachment point of the vortex distal to the stenosis, where the wall shear stress was lowest (zero). This value of the highest uptake rate was almost twice the average, whereas the uptake level was at a minimum at the stenosis itself where the wall shear stress was highest. The lowest uptake was only 60% of the average. These results provide strong support to our hypothesis, based upon the theory that, in addition to the flow induced changes to the biologic function of endothelial cells, the disturbed flow with slow recirculation itself favors the accumulation of atherogenic lipoproteins at the blood-endothelium boundary, therefore playing an important role in the localized pathogenesis and development of atherosclerosis.

Animals↗
PubMedDate not supplied

Localization of atherosclerosis in arterial junctions. Modeling the release rate of low density lipoprotein and its breakdown products accumulated in blood vessel walls.

Arterial bifurcations and surgically created junctions at anastomoses are places where blood flow may be disturbed and slow recirculation may occur. To address the hypothesis that such disturbances in flow may result in atherogenesis, the transfer of atherogenic substances from vessel wall to flowing blood was studied theoretically using a two dimensional T-junction model. Calculations showed that the transfer of atherogenic substances from vessel wall into flowing blood was suppressed in the two regions of disturbed flow, one in the main vessel, the other in the subsidiary vessel. The lowest release rates were at the points of flow separation and were found to be much lower than those in the undisturbed flow regions. Therefore, our mathematical model predicts that locally disturbed blood flows at arterial bifurcations and surgically created junctions are responsible for two distinct phenomena. First, they provide favorable conditions for the accumulation of LDL at the luminal surface, thus increasing the potential for lipid infiltration into the vessel wall, and second, they impair the transfer into blood of atherogenic substances accumulated in the vessel wall. Such mass transfer abnormalities may account for atherogenesis and late failures of arterial grafts at these sites.

Anastomosis, Surgical↗