The pig as an experimental animal in plastic surgery research for the study of skin flaps, myocutaneous flaps and fasciocutaneous flaps

The pig serves as an excellent model of skin flap research. Many flap types are available and flap designs can be modified easily for specific experimental requirements. Swine are large enough to permit multiple flaps and the skin color allows subjective observations of tissue circulation.     

Fasciocutaneous vessels in the upper arm: application to the design of new fasciocutaneous flaps

The principles of the blood supply to the upper arm are described. Despite the large, fleshy nature of the biceps and the triceps, the blood supply to upper arm skin is not from the underlying muscles, but is by fasciocutaneous perforators emerging along the medial and lateral intermuscular septa. Fifty dissections of preserved cadavers have shown that on the lateral side the fasciocutaneous perforators consistently arise from the middle collateral artery. The available length of this vessel and its diameter have been measured and are reported. The design of a flap based on this vessel, in a manner analogous to the Chinese forearm flap on the radial artery, is described.     

Effect of allopurinol on the survival of experimental pig flaps.

Allopurinol has been reported to improve cell survival in a variety of conditions, including the ischemia-reperfusion injury occurring in skin flaps. It has been suggested that the beneficial effect of allopurinol on rat skin flaps is through blockage of xanthine oxidase-generated oxygen-derived free radicals. We have previously reported on the lack of xanthine oxidase activity in the skin of humans and pigs as compared with that of rats. This current study attempts to improve skin and myocutaneous flap survival in pigs in two separate experiments using allopurinol. In the first experiment, a suspension of 50 mg/kg (N = 12) allopurinol resulted in no significant difference in the survival of control and treated flaps. Because of the negative results in the first experiment, a second experiment was designed making several changes. The length of the global ischemic insult was reduced from 8 to 6 hours, and allopurinol was administered as a solution of 300 mg/kg (N = 14). This higher dose is expected to produce complete inhibition of xanthine oxidase in this animal model. These changes resulted in three operative deaths, no improvement in skin-flap survival, and a decrease in myocutaneous flap survival. Allopurinol's therapeutic effectiveness and its mechanism of action in an ischemia-reperfusion injury model lacking xanthine oxidase activity are discussed.     

Prefabricated sensate myocutaneous and osteomyocutaneous free flaps: an experimental model. Preliminary report

Principles of neovascularization have been reported for the successful creation of a variety of muscle and bone free flaps. This study demonstrates a simple and effective technique for construction of prefabricated sensate myocutaneous and osteomyocutaneous free flaps in a rat model. These experiments were carried out in 20 Sprague-Dawley male rats. In half the animals, a sensate myocutaneous flap was constructed by sandwiching the superficial inferior epigastric vessels between a laterally based external abdominal oblique muscle flap and a laterally based skin flap served by an identified cutaneous nerve. A similar preparation included a piece of iliac crest bone. Two to three weeks later, now neovascularized by the sandwiched vessels, the flaps were harvested and transferred as free flaps with high reliability. An increased number of potential donor sites, the versatility of design, and the ability to customize flaps to the specific recipient-site needs are proffered.     

Survival of island flaps after tissue expansion: a pig model

Survival of island flaps after tissue expansion has been studied. Expanders were placed under each buttock flap of six minipigs and one side was expanded while the other was left empty as a control. Both flaps were then raised and isolated on their vascular pedicles in order to compare flap survival 7 days later. It was found that the survival lengths of the expanded flaps were approximately 50 percent greater than those of the delayed controls. Microangiography suggested that the diameter of the axial artery increased following expansion. In clinical practice this technique would provide a larger flap for reconstruction and the possibility of direct closure of the donor site. In addition, the observed increase in vessel caliber should facilitate the free tissue transfer of expanded flaps.     

Critical ischemia times and survival patterns of experimental pig flaps

Previous work on critical ischemia time suggested (1) a greater susceptibility of myocutaneous flaps over skin flaps to the ischemia reperfusion injury and (2) that duration of ischemia may affect the survival area of a flap. Using a pig model, 55 animals were operated on and the critical ischemia times and survival patterns of the buttock skin (n = 85) and latissimus dorsi myocutaneous (n = 88) island flaps were determined after being submitted to 0, 2, 4, 6, 8, 10, 12, 14, and 16 hours of normothermic ischemia. The average critical ischemia times (CIT50) were determined to be 9 and 10 hours for the buttock skin and latissimus dorsi myocutaneous flaps, respectively. Percentage of total area surviving (%TAS) in those flaps which did survive was adversely affected by increases in the ischemic interval in both flap models. A statistically significant decrease in percentage of total area surviving was found after 6 and 8 hours of ischemia for the buttock skin and latissimus dorsi myocutaneous flaps, respectively.     

Ischemic injury to enteric free flaps: an experimental study in the dog

Enteric free flaps have proven to be useful for reconstructing the cervical esophagus. Although jejunum is favored, the rationale for this is not at all clear. We have postulated that resistance to warm ischemia varies in different regions of the gut. An experiment was carried out in 10 mongrel dogs in which 10-cm segments of proximal, middle, and distal small bowel were isolated on single vascular pedicles. In each portion of the gut there were three segments: a control, a segment subjected to 60 minutes of warm ischemia, and a segment subjected to 120 minutes of warm ischemia. The following day each animal was reexplored, and the viability of bowel segments was assessed visually and with fluorescein. All control segments were viable at 24 hours. Twenty segments were subjected to 1 hour of warm ischemia, and all but two were viable. Nineteen gut segments were subjected to 2 hours of warm ischemia. Seven of eight proximal segments were viable, two of five midsegments were viable, and zero of six distal segments were viable. Survival in the distal portion compared to the proximal portion was significantly less (p less than 0.01). It appears from this study that isolated distal small bowel segments are less resistant to warm ischemia than proximal segments.     

The timing and nature of neovascularization of jejunal free flaps: an experimental study in a large animal model.

The present study was designed (1) to determine whether a free jejunal transfer in a large animal model can develop collateral circulation that is adequate to maintain viability after division of the pedicle and (2) to determine the earliest time pedicle ligation is safe after transplantation. A 15-cm jejunal segment was transferred to the necks of 18 dogs weighing 25 to 35 kg. The bowel segment was inset longitudinally under the skin on one side of the neck, partially covered by the neck muscles, and the mesenteric vessels were anastomosed to recipient vessels in the neck. The proximal and distal bowel stomas were exteriorized through skin openings 12 cm apart and matured. The dogs were subjected to ligation of the vascular pedicle at different intervals: postoperative day 7 (group I, n = 3), day 14 (group II, n = 5), day 21 (group III, n = 5), and day 28 (group IV, n = 5). Blood perfusion was measured in the proximal and distal bowel stomas before pedicle division (control) and 24 hours later using hydrogen gas clearance and fluorescein dye. Bowel necrosis was analyzed using planimetry. The bowel was also stained with hematoxylin and eosin and factor VIII, and new blood vessels were counted. Mean values (+/- standard deviation) were compared with control values for each test and with normal values in the intact bowel using analysis of variance with Neumann-Keuls post-hoc test for multiple comparisons. No jejunal free flaps survived when the vascular pedicle was divided 1 week postoperatively. Bowel survival was 60 percent at 2 weeks, 83 percent at 3 weeks, and 100 percent at 4 weeks. Hydrogen gas clearance values (ml/min/100 g) were 49.6 +/- 8.7 in the mucosa of the intraabdominal jejunum and 37.9 +/- 9.4 in the jejunum that was transferred to the neck before division of the pedicle. Twenty-four hours after pedicle division, hydrogen gas clearance values were 2.8 +/- 6.4 in group I (p < 0.05), 22.4 +/- 12.4 in group II, 23.9 +/- 9.3 in group III, and 34.2 +/- 7.5 in group IV. FluoroScan readings in the transferred jejunum were 201 +/- 7.2 in the control group, 9.3 +/- 2.8 in group I (p < 0.05), 79.1 +/- 10.6 in group II, 66.2 +/- 7.3 in group III, and 164 +/- 11.9 in group IV. New vessel formation as identified by factor VIII staining correlated with increasing bowel perfusion and flap survival rate. Bowel neovascularization, perfusion, and survival increased progressively 1 week after transfer. Significant portions of the transferred bowel will neovascularize and survive as early as 2 weeks postoperatively. However, a minimum of 4 weeks before ligation of the pedicle is necessary to maximize flap perfusion and guarantee survival.     

A new experimental model for myocutaneous flaps: latissimus dorsi of the rabbit--an anatomic study

A new experimental model, the latissimus dorsi flap of the rabbit, was studied. This was found to be a relatively inexpensive research model. Its use is advocated for composite tissue transfer as transposition, island, or free myocutaneous flaps.     

An experimental model of ameboma in guinea pig.

Among the wide variety of clinicopathological manifestations of intestinal amebiasis, amebomas occur rarely and their pathogenesis is not well understood. When cholesterol-fed, 2- to 4-week-old guinea pigs were infected intracecally with a virulent, monoaxenic strain of Entamoeba histolytica, gross and histologically characteristic amebomas developed in 85% of the animals by the 3rd day, in 94% by the 9th day, and in 96% by the 12th day postinfection, by which time most of them had died. Amebomas were confirmed by histopathology. Thus, a model of consistent production of amebomas was documented.     

Regional intravascular sympathetic blockade for better results in flap surgery: an experimental study of free flaps, island flaps, and pedicle flaps in the rabbit ear

Flap survival is still a major problem in reconstructive surgery. Increased flap survival after systemic administration of drugs inhibiting the adrenergic system has been reported in experimental studies. The clinical use, however, is restricted by systemic side effects. It has been demonstrated that, using guanethidine, an effective regional intravascular sympathetic (RIS) block can be obtained without systemic effects. Using this type of block, an experimental study was made on the survival and quality of different types of flaps in the rabbit ear. The results obtained in 72 flaps created in the ears of 36 rabbits were assessed by the extent of flap edema, peripheral neovascularization, flap temperature, and flap surviving area. The RIS block reduced edema and scab formation, caused higher flap temperatures, better neovascularization, and increased surviving flap area, as compared with equal flaps in the untreated contralateral ear of the same animal. The effect of RIS block may be considered as a "pharmacological delay" procedure. From the experiments as well as clinical experience, it may be concluded that this technique is a safe and effective procedure. Therefore, the RIS block method is recommended for clinical use in flap techniques in extremities of man.     

Virus-neuron interaction: an experimental model

Conclusion These examples demonstrate the usefulness of embryonic neurons for investigation ofneurotropic virus pathogenesis studies. The different steps of viral interactions of neurotropicviruses with the brain necessitate studies of the intrinsic neural properties of the infected cells:1) entry of virus into the intra-cellular compartment, 2) transport of virus from one brainstructure to another brain area, 3) replication of virus in the host-cells, 4) altered brainfunctions. Understanding the mechanisms of neural pathogenesis is a prerequisite for theelaboration of antiviral strategies based upon recovery of the brain from functional alterationsusing drugs active on brain functions.     

Muscle flaps in the management of vascular grafts in contaminated wounds: an experimental study in dogs

This study evaluates in an animal model the efficacy of muscle flaps in protecting the fabric vascular prosthesis when placed in contaminated wounds. A total of 20 adult mongrel dogs received a 2-cm interpositional polytetrafluoroethylene (PTFE) graft to each femoral artery at the groin level. During the surgical procedure, the wounds were inoculated with a Staphylococcus aureus suspension containing either 1 x 10(4) or 1 x 10(5) organisms per milliliter. In half the animals, the grafts were wrapped with a distally based sartorius muscle flap before a standard two-layer closure was completed. One month after the surgery, all the animals were sacrificed and quantitative cultures were performed of the grafts and wounds. The muscle flaps were capable of protecting the vascular prosthesis with inoculums up to 1 x 10(4) organisms (p less than 0.05), but at greater bacterial contamination their efficacy was no longer significant.     

The pig as an experimental model for elucidating the mechanisms governing dietary influence on mineral absorption

This review highlights the similarities between pigs and humans and thereby the value of the porcine human nutritional model, and reviews some of the more recent applications of this model for nutritional research.     

Glucose metabolism in experimental skin flaps

The metabolism of glucose by rat abdominal skin flaps has been investigated at various times after flap elevation. Biopsies of flap skin taken during the first 3 days after flap elevation and incubated in vitro show a marked increase in glucose consumption and lactate production compared with normal skin. At the same time, flap tissue reserves of glucose and glycogen are lower than those of normal skin. Providing that some circulation persists, the magnitude of the changes in glucose metabolism is proportional to the degree of ischemia experienced by the flap tissue in vivo. In most cases, glucose consumption and lactate production return to normal by the end of the first week after flap elevation. These experiments thus further define a major ischemia-induced shift to anaerobic metabolism (glycolysis) that occurs in skin flaps.     

Arteriovenous shunting and regional blood flow in myocutaneous island flaps: an experimental study in pigs

In eight pigs, total blood flow, regional capillary blood flow distribution, and arteriovenous (AV) shunting were studied during the first 4 postoperative hours after elevation of a myocutaneous rectus abdominis island flap. Capillary blood flow and AV shunting were measured using radioactive microspheres before flap creation and 1 and 4 hours after surgery. Total blood flow, measured continuously as venous outflow, increased in the first postoperative hour (p less than 0.05). Elevation of the flap caused a slight decrease in skin capillary blood flow (p less than 0.05), whereas muscular capillary blood flow increased (p less than 0.01). AV shunting accounted for 50 percent of the total flap blood flow, whereas it was negligible in the abdominal wall prior to flap elevation. Thus stalk blood flow, skin appearance, and skin temperature may be poor indicators of nutritional capillary perfusion. However, the clinical and nutritional consequences of these findings remain to be established.