Biomedical subjects

W X Zhang

Publications and source records attributed to W X Zhang.

At least 37 records · Page 2Linked to original sources

PubMed1999

Use of an acellular dermal allograft for dural replacement: an experimental study.

OBJECTIVE: In this study, a nonimmunogenic, acellular, dermal collagen matrix termed XenoDerm (LifeCell Corp., The Woodlands, TX) was examined for use as a dural replacement material in a porcine model. This model was used to investigate whether AlloDerm (LifeCell), an almost identical material made from human dermis, could be safely used in neurological surgery. METHODS: Bilateral temporoparietal dural defects were surgically created in 12 Yucatan minipigs. One side was repaired with autologous pericranium, and the other was repaired with XenoDerm. The pigs were killed after 1, 3, or 6 months, and the areas of dural repair were collected and examined macroscopically and histologically. XenoDerm is derived from porcine skin collected in thin sheets. It is processed so that the epidermis and all dermal cells are removed without disruption of the collagen matrix, rendering the material immunogenically inert and resistant to calcification. It is packaged as a freeze-dried sheet and is easily rehydrated at the time of surgery. RESULTS: There were no postoperative complications, and all pigs survived. Both grafts performed well as dural replacements in all cases. There was no macroscopic evidence of inflammation or cerebrospinal fluid leakage. The XenoDerm grafts were intact, retained their original dimensions, and resembled the surrounding dura. The autologous pericranial grafts, in contrast, were thicker than when implanted and had bony excrescences firmly adhering to their surfaces. Again, however, there was no evidence of cerebrospinal fluid fistulae. There was no gross adherence to the underlying meninges or brain tissue in any specimen. Repopulation by fibroblasts and neovascularization were evident in the XenoDerm grafts as early as 1 month after surgery; by 3 months, the XenoDerm had been remodeled to assume the connective tissue appearance of the surrounding dura. CONCLUSION: In this porcine model, an allograft of acellular dermis is a nearly ideal dural replacement. AlloDerm, the human equivalent of XenoDerm, would be an allograft of acellular dermis after implantation in human subjects. On the basis of this study and previous work with AlloDerm in other reconstructive applications, it is proposed that this material could be similarly used for duraplasty in human subjects.

Animals↗

PubMed1999

[Mitochondrial DNA genetic polymorphism of Drosophila immigrans in China].

This article uses RFLP to analyze the mitochondrial DNA(mtDNA) variation in geographic populations of Drosophila immigrans from 6 regions of mainland of China. With the use of fourteen restriction endonucleases, we only discoveried a total of 11 mtDNA haplotypes among 46 isofemale lines. The mean value of I is 0.833, the mean value of J is 0.797, and the estimated Gst value is only 16.8%. We recognized that the genetic structures among the geographic populations of D. immigrans are highly uniform, and the genetic differentiation rate is low. The UPGMA analysis of nucleotide diversity of the 6 populations shows specific characteristics of mtDNA variation in population of Huayang, Qinling Mountains Regions. From the haplotypes special included in each population, the event that the population spread into the high altitute localities of Yunnan perhaps happened more recently. Referring other references, we inferred the population of D. immigrans distributed in mainland of China is more original than that in Chinese Taiwan and Japan.

Animals↗

PubMed1999

[Integrated protection capability afforded by a new type capstan anti-G equipment and anti-G straining maneuver].

Objective. To investigate the integrated protection capability afforded by a new type capstan anti-G equipment and anti-G straining maneuver, as a result we discussed the feasibility of protection for 8 G 10 s (rapid onset runs at 2 G/s) acceleration using an associated precept with the above both anti-G measures. Method. This study was accomplished using the human centrifuge with rapid onset at 2 G/s. First, we determined the relaxed +Gz tolerance of nine male aviation students, and then determined theirs most + Gz tolerance while thereinto the five aviation students using a new type capstan anti-G suit (NKH) + a new type anti-G valve (NKT) + L-1 anti-G straining maneuver (L-1) and the other four aviation students using a new type capstan counterpressure suit (NDC) + the new type anti-G valve (NKT) + L-1. Result. The most +Gz tolerance of five students was 8.80 +/- 0.27 G while using NKH + NKT + L-1 and was higher than their relaxed +Gz tolerance at 4.60 +/- 0.42 G (P< 0.01) and that the most +Gz tolerance of four students was 8.75 +/- 0.50 G while using NDC + NKT + L-1 and was higher than their relaxed +Gz tolerance at 4.50 +/- 0.46 G (P< 0.01). Conclusion. Pilot will be capable against the 8 G 10 s (rapid onset runs at 2 G/s) effectively using the new type capstan anti +/- G equipment and anti +/- G straining maneuver, and the provided precept has availability.

Acceleration↗

PubMed1999

[Technical consideration of setting up a specification for human centrifuge evaluation of anti-G equipment].

Anti-G equipment needs to be evaluated using human centrifuge before further developed. However, there isn't a general specification for human centrifuge evaluation of anti-G equipment. From related literature and from our over thirty years experience in this area, we sum up to five aspect technical consideration below: human centrifuge, medical specification for using human in +Gz stress experiment, anti-G equipment experimental assembly, principle should be abided by during human centrifuge evaluation of anti-G equipment. We hope that the technical considerations mentioned in the paper should be helpful to the work of setting up a specification for human centrifuge evaluation anti-G equipment. After we have a specification, the research will be conducted orderly and the anti-G [correction of an-G] equipment will be developed sequentially.

Acceleration↗

PubMed1998

Effect of time on the viability of ischemic skin flaps treated with vascular endothelial growth factor (VEGF) cDNA.

This study examined the efficacy of gene therapy on wound healing. The authors investigated whether delivery of the gene encoding a particular cytokine, known to be important in angiogenesis, could affect ischemic skin flaps. Anterior abdominal skin flaps, based solely on the epigastric artery and vein, were created in the Sprague-Dawley rat model. At the time of elevation, the arterial pedicle supplying each flap was infused either with the gene for vascular endothelial growth factor (VEGF) or physiologic saline alone. The flaps were resutured into place and observed for a period of either 4 or 3 days, at which time the pedicle was ligated. Twenty minutes following ligation, blood flow in the flaps was measured by dye fluorescence. Tissue viability of the flaps was subsequently measured by planimetry after a period of 7 days. Flaps that received the VEGF gene and were ligated at 4 days had an average dye fluorescence index (DFI) of 31.1 following ligation, and 93.9 percent viable tissue after 7 days. Flaps that received saline alone, and were ligated following a similar interval, had an average DFI of 14.0 and 31.9 percent viable tissue. Among the subjects that were ligated at 3 days, only a single, gene-infused flap had any noticeable viable tissue after 7 days. The DFI of these groups was 11.0 for the gene-infused group and 22.1 for the saline-infused group. The results suggest that delivery of the gene for VEGF can improve the survival of ischemic skin flaps, but that the effect of gene therapy is not limitless.

Analysis of Variance↗

PubMed1998

Locally administered vascular endothelial growth factor cDNA increases survival of ischemic experimental skin flaps.

Microvascular surgery has emerged as an attractive area for recent advances in the field of gene therapy. The present study investigated the survival of ischemic, experimental skin flaps after treatment with the gene encoding vascular endothelial growth factor (VEGF). In 30 Sprague-Dawley rats, anterior abdominal skin flaps supplied by the epigastric artery and vein were created. Ten animals were treated with a mixture of liposomes and the cDNA encoding the 121-amino acid isoform of VEGF. Another 10 animals were treated with control plasmid DNA and liposome transfection medium; a third group of 10 animals was given physiologic saline. Each solution was injected directly into the femoral artery distal to the origin of the epigastric pedicle supplying the flap. Four days after injection, the pedicle was ligated and blood flow in the flap was approximated using dye fluorescence. Seven days later, the amount of viable tissue within the flap was measured by planimetry. After the animals were killed, specimens from both the operated and nonoperated sides of the abdomen were harvested for immunohistologic evidence of VEGF protein expression. Average dye fluorescence indices of the three groups (VEGF cDNA, control plasmid, and saline) 2 hours after pedicle ligation were 35.9, 23.9, and 53.9 percent, respectively (p < 0.05). Compared with the two control groups, flaps receiving VEGF cDNA had significantly greater tissue viability at the end of 7 days: 93.9 versus 28.1 percent for the control plasmid DNA group and 31.9 percent for the saline group (p < 0.05). Immunohistochemical staining documented increased deposition of VEGF protein in flaps that were infused with the VEGF cDNA versus saline alone (p < 0.05). The results indicated that the survival of ischemic tissues can be enhanced by administration of a cDNA encoding VEGF, a protein known to be important in the process of angiogenesis and wound healing.

Animals↗

PubMed1997

Continuous tissue oxygen tension measurement as a monitor of free-flap viability.

Early recognition of vascular compromise within microvascular free-tissue transfers is essential if reexploration is to prove successful. Tissue oxygen tension is increasingly recognized to be a sensitive and reliable index of tissue perfusion, and preliminary studies suggest that it may be of value in the assessment of free-flap viability. We describe our investigation into the application of an implantable microcatheter oxygen sensor in the monitoring of free flaps used in head and neck and extremity reconstruction. In a preliminary study using the rabbit model, we sought to evaluate the response of oxygen tension as an index of tissue perfusion in myocutaneous (n = 20) and osteomyocutaneous flaps (n = 5) under conditions of arterial and venous occlusion. A clinical study was then undertaken to evaluate the role of this method in the monitoring of surface and buried free flaps. In 30 heterogeneous free-tissue transfers, sensors placed intraoperatively were used to provide continuous information about flap oxygen tension (mean monitoring period 3.2 +/- 0.8 days). The data generated were correlated with changes in clinical parameters and routine flap observations. Results for experimental and clinical data have confirmed the efficacy of continuous tissue oxygen measurements using this device as a method that provides an objective, recordable index of free-tissue transfer viability in a variety of circumstances and vascular events. Tissue oxygen tension is a suitable index by which to evaluate flap viability with the probe placed in muscle or bone but is unreliable when used for the monitoring of revascularized cutaneous flaps.

Animals↗

PubMed1996

Periadventitial delivery of heparin in the prevention of microvenous thrombosis.

PURPOSE: In spite of advances in technique and instrumentation, microvascular free tissue transfer remains associated with a persistent risk of flap failure. The use of systemic anticoagulants to overcome the formation of vasoocclusive thrombi at reactive anastomotic sites is associated with a high rate of flap hematoma and is ill advised in the operative setting. The purpose of this study was to investigate the use of a biodegradable, nontoxic polymer gel (polyvinyl alcohol, PVA) to effect a sustained localized release of perivascular heparin around thrombogenic venous anastomoses. MATERIALS AND METHODS: A modified adventitial inclusion model was created in the femoral vein of 64 adult female Sprague-Dawley rats. Animals were divided into four experimental groups: 1) no treatment (controls), 2) periadventitial PVA gel contained in a vicryl chamber, 3) periadventitial PVA gel mixed with heparin, and 4) systemic heparin (intravenous pump). Patency rates in the femoral vein were checked at 10 minutes, 1 hour, 1 day, and 4 days after surgery. Systemic coagulation parameters and histology (scanning electron microscopy, SEM) were assessed in representative animals from all groups. RESULTS: Patency rates for experimental groups showed a significant improvement in animals treated with PVA/heparin and systemic heparin over controls. Wound hematomas occurred in 7 of 16 animals in group 3, and in 4 of 16 animals in group 4. Activated partial thromboplastin times were elevated in group 4 only (> 150 seconds). CONCLUSIONS: Continuous release of periadventitial heparin using a polymeric delivery system may represent an efficient means of attenuating the reactivity of microvenous anastomoses without affecting systemic coagulation parameters. In this model, however, its use was associated with a high rate of local wound hematoma.

Animals↗

PubMed1996

Thrombolysis at a controlled pressure prolongs the survival of skin flaps treated with superoxide dismutase.

The role of thrombolysis in reestablishing patency in the microcirculation following ischemia, and thereby improving the efficacy of agents attenuating reperfusion injury, such as the oxygen free radical scavenger, superoxide dismutase (SOD), was investigated in a rat model. Abdominal skin flaps were subjected to normothermic ischemia induced by complete occlusion of the pedicle for periods of 12, 13, 14, 16, 18, 20, 22, and 24 hr. In Group 1 (n = 64), all animals received flap washout using 100,000U urokinase (manual injection) followed by 7,500 IU SOD given intra-arterially immediately prior to reperfusion. Animals in Group 2 received flap washout consisting of 100,000U urokinase given via a pressurized delivery system, followed by 7,500 IU SOD. Results demonstrated a statistically significant improvement in flap survival in Group 2. The authors concluded that thrombolytic therapy may be useful in improving the delivery of agents, such as SOD, which attenuate reperfusion injury in skin flaps.

Animals↗

PubMed1996

Increased patency of artificial microvascular grafts using arteriovenous fistula loops: a two-stage procedure for lengthening the pedicle of free-tissue transfer.

The effect of a high-flow system on the patency of artificial microvascular grafts (AMG) was investigated using arteriovenous (A-V) fistula loops made of polytetrafluoroethylene (PTFE) in a clinically useful longer length. At a second stage, the A-V loops, matured for 7 days, were used as recipient conduits for free-tissue transfer. The patency rates of 5-cm long PTFE A-V fistula loops were compared with 5-cm and 1-cm long interpositional micrografts in a rat model. The patency rate of the loops at 7 days was 80 percent, compared to 0 percent for both the 5-cm and 1-cm interpositional grafts. A-V fistula loops matured for 7 days in vivo were divided in their midsections and used as arterial and venous conduits (each 2.5 cm long) for free epigastric flaps (3 x 6 cm) raised from the contralateral groin. Sixty-seven percent (8/12) of the free flaps were viable at 7 days. The A-V fistula loop in a high-flow system has a beneficial effect in maintaining patency of AMGs. PTFE fistula loops matured for 7 days can be used as arterial and venous conduits for microsurgical tissue transfer in rats.

Animals↗

PubMed1996

Combination therapy for salvaging a failing, experimental skin flap.

The failing free flap remains a major problem for the reconstructive surgeon. Many and varied pharmacologic agents have been utilized to reverse the effects of ischemia in these flaps. Treatments have been aimed at inhibiting presumed causative factors in the no-reflow phenomenon. Therapy has generally been single in nature and designed to affect only one of these presumed factors. In this study, several pharmacologic agents were utilized individually or in combination therapy as postischemic washouts, in an effort to attack the multiple causative factors in the no-reflow phenomenon and to improve flap survival in a rat abdominal skin flap model. The treatment agents included lactated Ringer's, superoxide dismutase, and urokinase, with each used independently as a postischemic perfusion washout. Combination therapy utilized an initial postischemic perfusion with urokinase, followed by a second perfusion washout with superoxide dismutase. After 18 hr of primary ischemia, there was increased flap survival in the animals undergoing perfusion washout with either superoxide dismutase alone or with combined urokinase and superoxide dismutase washouts, compared to all other treatments (p < 0.001). It was found that flaps undergoing combined urokinase and superoxide dismutase postischemic perfusion washouts demonstrated significantly improved survival after 20 hr of primary ischemia, compared to all other therapies (p < 0.05). By demonstrating improved survival when a thrombolytic agent is used in conjunction with an oxygen free radical scavenger, these findings may have implications in the treatment of clinically failing free flaps.

Animals↗

PubMed1996

Reappraisal of the inferior epigastric flap: a new neurovascular flap model in the rat.

An anatomic, histologic, and electrophysiologic study was carried out in order to determine the distribution and cutaneous sensory territory of the epigastric nerve in the rat. Results for nerve staining (Sihler's method) and electrophysiologic nerve mapping indicate that the neurosome of the epigastric nerve has a different autonomy than the vascular territory of the inferior epigastric artery. Based on these findings, an experimental model for neurovascular free-tissue transfer is proposed.

Abdomen↗

PubMed1995

Use of the guinea pig flank flap in skin flap research.

A variety of flaps in laboratory animals have been designed that propose to parallel the behavior of human skin under different experimental conditions. In the search for a readily available and affordable island skin flap model that combines reliable anatomy with a pedicle of substantial size, we have designed in the guinea pig a cutaneous flap based on the superficial circumflex iliac artery and vein. In 22 adult female Hartley guinea pigs, an 8 x 4 cm flank flap based on the superficial circumflex iliac pedicle was raised, and its characteristics were evaluated for applications to skin flap research. Dermofluorometric studies were performed that confirm the vascularity of this flap, and 100% survival of the flap was seen 5 days after surgery in all animals. Of particular benefit was the demonstration that both afferent and efferent blood samples can be taken from the pedicle directly, which allows for the direct quantification of plasma markers after physiologic insults to the skin flap, such as burn or ischemia. This anatomically reliable and easily dissected flap lends itself well to preliminary skin flap research and may contribute to standardization of a model for further studies examining the behavior of skin microcirculation under adverse physiologic conditions.

Animals↗

PubMed1995

Improved efficacy of urokinase further prolongs ischemic skin-flap survival.

Salvage of a free-tissue transfer, when postoperative vascular compromise is detected, depends largely upon the restoration of a patent microcirculation. The therapeutic efficacy of thrombolytics infused directly into the failing flap has been clearly demonstrated. In this experiment, the authors investigated whether the method of selective administration of urokinase to failing skin flaps in 68 Sprague-Dawley rats had any effect on flap survival. In one group of animals, postischemic flaps were perfused with 100,000 IU of urokinase given by manual injection, and via a pressurized delivery system (150 mmHg) in the other group. Flap survival was assessed at 7 days. A significantly greater survival was seen in flaps treated with urokinase by controlled pressure infusion (p < 0.01). This simple method is suggested to increase the efficacy of urokinase used in the context of flap salvage.

Animals↗

PubMed1995

Evaluation of a continuous systemic infusion of iloprost, a stable PGI-2 analog, on the survival of experimental skin flaps.

Numerous investigators have attempted to enhance the survival of ischemic experimental skin flaps using various pharmacologic manipulations. Recently, the authors' laboratory demonstrated the beneficial effect of iloprost, a stable PGI2 analogue, as a post-ischemic perfusion washout, in improving the survival of ischemic skin flaps. The rat unilateral abdominal skin flap, based on the superficial epigastric vessels, was utilized in this study involving 30 animals. The animals were divided into three different treatment groups, with ischemic periods of 16 and 18 hr. Perfusion washouts were performed at the completion of the various ischemic periods. Alzet osmotic pumps were used to deliver a continuous systemic infusion of iloprost for 7 days postoperatively. The groups consisted of the following: Group 1 (single ILO)--perfusion washout with iloprost only; Group 2 (continuous LD ILO)--low-dose systemic iloprost infusion (0.066 mcg/kg/min) and perfusion washout with iloprost; and Group 3 (continuous HD ILO)--high-dose systemic iloprost infusion (0.1 mcg/kg/min) and perfusion washout with iloprost. The percentage of flap survival was assessed on postoperative day 7. Skin flaps of the animals receiving the continuous systemic infusion of iloprost were noted to have varying percentages of survival, while skin flaps undergoing perfusion washout only were found to have either complete survival using a continuous systemic infusion of iloprost, compared to iloprost perfusion washout alone. In addition, the hypotensive side effects of systemic iloprost infusion limit its use in the rat skin-flap model.

Animals↗

PubMed1995

A standardized model of microvenous thrombosis.

A standardized model of venous thrombosis is necessary when evaluating potential antithrombotic or thrombolytic agents in microsurgery. Previous studies have shown the adventitial "tuck" model to be advantageous in terms of the vascular reactivity achieved and the relative ease of performance. However, variability exists in the current design, due to the lack of standardized dimensions of the adventitial flap. Two variations of this model are presented which attempt to overcome this problem, and their reproducibility is compared to the inversion graft model of venous thrombosis in the rat femoral vein. The "femoral vein flap" is suggested as a suitable model to simulate anastomotic thrombosis during microvenorrhaphy.

Abdominal Muscles↗

PubMed1994

Use of urokinase during secondary ischemia in experimental skin flaps.

The ability of urokinase to salvage experimental flaps after a secondary ischemic insult was investigated in a rat model. Unilateral abdominal island skin flaps based on the superficial inferior epigastric vessels were raised and subjected to either 4 or 6 hours of primary ischemia followed by 12 hours of reperfusion and varying lengths of secondary ischemia. At the conclusion of secondary ischemia, the flaps were perfused with either lactated Ringer's solution or urokinase. One group of flaps served as a control and received no postischemic perfusion washout. The secondary critical ischemia time at which 50% of the flaps failed clinically was greater for flaps perfused with urokinase. Furthermore, the survival rates for all flaps perfused with urokinase were significantly greater than either control flaps or flaps perfused with lactated Ringer's solution (p < 0.05). Flap survival decreased significantly in all groups with increasing primary and/or secondary ischemia time (p < 0.05).

Animals↗

PubMed1994

Iloprost improves survival of ischemic experimental skin flaps.

The ability of the prostacyclin analogue iloprost to improve survival of ischemic experimental skin flaps was investigated. Unilateral island skin flaps based on the superficial inferior epigastric vessels were raised in 70 rats and subjected to varying lengths of primary ischemia. The flaps were divided into the following four groups: group I, no perfusion washout; group II, postischemic washout with lactated Ringer's solution; group III, postischemic washout with urokinase; and group IV, postischemic washout with iloprost. Flap survival rates for group IV were significantly higher than all other groups (p < 0.05). The primary ischemia time at which 50% of the flaps failed was 8.9 hours for group I, 9.5 hours for group II, 13.3 hours for group III, and 15.3 hours for group IV. This is the first study to investigate the effect of iloprost on skin flap survival. Iloprost was found to be significantly more effective than urokinase in salvaging ischemic experimental skin flaps.

Animals↗