Ischemia in wound healing. I: Design of a flap model--changes in blood flow

The rat as an animal model in chronic wound research: An update

The increasing global prevalence of chronic wounds underscores the growing importance of developing effective animal models for their study. This review offers a critical evaluation of the strengths and limitations of rat models frequently employed in chronic wound research and proposes potential improvements. It explores these models in the context of key comorbidities, including diabetes, venous and arterial insufficiency, pressure-induced blood flow obstruction, and infections. Additionally, the review examines important wound factors including age, sex, smoking, and the impact of anesthetic and analgesic drugs, acknowledging their substantial effects on research outcomes. A thorough understanding of these variables is crucial for refining animal models and can provide valuable insights for future research endeavors.

Modeling Wound Chronicity In Vivo: The Translational Challenge to Capture the Complexity of Chronic Wounds

In an aging society with common lifestyle-associated health issues such as obesity and diabetes, chronic wounds pose a frequent challenge that physicians face in everyday clinical practice. Therefore, nonhealing wounds have attracted much scientific attention. Several in vitro and in vivo models have been introduced to deepen our understanding of chronic wound pathogenesis and amplify therapeutic strategies. Understanding how wounds become chronic will provide insights to reverse or avoid chronicity. Although choosing a suitable model is of utmost importance to receive valuable outcomes, an ideal in vivo model capturing the complexity of chronic wounds is still missing and remains a translational challenge. This review discusses the most relevant mammalian models for wound healing studies and provides guidance on how to implement the hallmarks of chronic wounds. It highlights the benefits and pitfalls of established models and maps out future avenues for research.

Animal experimental models of ischemic wounds - A review of literature

Critical limb ischemia is a serious form of peripheral arterial disease (PAD). The consequences of lower limb ischemia are pain, claudication and chronic non-healing wounds. Patients with diabetes are especially at a high risk for developing non-healing ulcers. The most serious complication is major amputation. For this reason, there is a significant medical requirement to develop new therapies in order to prevent the progression of PAD. For research purposes, it is crucial to find an appropriate model of chronic ischemia to explore the processes of wound healing. According to recently acquired information, rodents are currently the most commonly used animals in these types of studies. The main advantage of using small animals is the low financial cost due to the relatively small demand for food, water and living space. The disadvantage is their anatomy, which is different from that of humans. Larger animals have a more human-like anatomy and physiology, but they require more expense and space for housing. A bipedicle skin flap and its modifications are popular models for ischemic wounds. In order to secure healing through re-epithelisation, as opposed to contraction in rodents, there is a need to remove the panniculus carnosus muscle. Wounds in other experimental animals heal primarily through re-epithelisation. The application of a silicone mesh underneath the flap prevents vascular regrowth in ischemic tissue. There is an ongoing effort to create in vivo diabetic models for chronic ulcer research. This work presents an overview of existing animal models of ischemic wounds.

＜Editors' Choice＞ Effect of postoperative doxorubicin administration on ischemic wound healing

Some patients undergo postoperative chemotherapy despite showing impaired wound healing after a major surgery. We speculated that postoperative chemotherapy further delays wound healing in these patients. This study aimed to compare the effects of doxorubicin (DXR) in ischemic skin flap and normal incisional wound models after surgery. A 2-cm incisional wound was made in group 1 rats, and saline was injected intravenously, following surgery on the same day. Incisional wound was made in group 2–5 rats, and 8 mg/kg DXR was injected intravenously, following surgery on the same day and after 7, 14, and 21 days respectively. H-shaped double flaps were made in group 6 rats, and saline was injected intravenously, following surgery on the same day. Flaps were made in group 7–10 rats, and 8 mg/kg DXR was injected intravenously, following surgery on the same day and after 7, 14, and 21 days respectively. On days 7, 14, 21, and 28 after surgery, the suture wounds were removed, tensile wound strengths were measured, and tissue samples were collected for histopathological evaluation. The tensile strength was significantly lower in the DXR-treated groups than in the control groups for both ischemic skin flaps and incision wounds. Additionally, the cross effect between DXR and ischemia was not significant. On pathological examination, DXR showed atrophic skin changes and degeneration of skin appendages on days 14–21 after the surgery in both the models. DXR decreased the wound tensile strength and caused an atrophic change in the ischemic wound.

Effects of Acellular Amniotic Membrane Matrix and Bone Marrow-Derived Mesenchymal Stem Cells in Improving Random Skin Flap Survival in Rats

BACKGROUND

The necrotic skin flap represents a great challenge in plastic and reconstructive surgery. In this study, we evaluated the effect of bioscaffolds, acellular amniotic membranes (AAMs), and bone marrow-derived mesenchymal stem cells (BM-MSCs) on random skin flap (RSF) survival in rats by applying a cell-free extracellular matrix scaffold as a supportive component for the growth and proliferation of BM-MSCs on RSFs. AAM matrix scaffolds were created by incubating AMs in ethylenediaminetetraacetic acid 0.05% at 37°C, and cell scrapers were used.

OBJECTIVES

The aim of the present study was to assess the effect of AAM as a scaffold in TE, and combined with transplanted BM-MSCs, on the survival of RSFs and on the biomechanical parameters of the incision-wound flap margins 7 days after flap elevation.

MATERIALS AND METHODS

BM-MSCs and AAMs were transplanted into subcutaneous tissue in the flap area. On the 7th postoperative day, the surviving flap areas were measured using digital imaging software, and the flap tissue was collected for evaluation. Forty rats were randomly divided into four groups of 10 each: group 1 received an AAM injection; group 2 underwent BM-MSC transplantation; group 3 received both AAM injection + BM-MSC transplantation; and group 4 was the control group, receiving only saline.

RESULTS

The survival area in the AAM/BM-MSC group was significantly higher than in the control group (18.49 ± 1.58 versus 7.51 ± 2.42, P < 0.05). The biomechanical assessment showed no significant differences between the experimental groups and the control group (P > 0.05), and there was no correlation with flap survival.

CONCLUSIONS

Our findings showed that the treatment of flaps with BM-MSC and AAM transplantations significantly promoted flap survival compared to a control group. The viability of the flap was improved by combining BM-MSCs with AAM matrix scaffolds.

Polydeoxyribonucleotide restores blood flow in an experimental model of ischemic skin flaps

BACKGROUND

Ischemia is a major factor contributing to failure of skin flap surgery, which is routinely used for coverage of wounds to prevent infection and to restore form and function. An emerging concept is that adenosine A(2A) receptors can improve tissue oxygenation by stimulating angiogenesis, likely through vascular endothelial growth factor (VEGF). This study assessed the ability of polydeoxyribonucleotide (PDRN) to restore blood flow and improve wound healing, acting through the A(2A) receptor, in a rat model of ischemic skin flaps.

METHODS

The H-shaped double-flap model was used in male Sprague-Dawley rats. After surgical procedures, the animals were randomized to receive intraperitoneal PDRN (8 mg/kg) or vehicle (NaCl 0.9%). Rats were euthanized 3, 5, and 10 days after skin injury, after the evaluation of skin perfusion by laser Doppler. The wounds underwent histologic analysis and were measured for VEGF messenger RNA and protein expression, hypoxia inducible factor-1-α (HIF-1α), and inducible nitric oxide synthase (iNOS) protein expression, and nitrite content.

RESULTS

Blood flow markedly increased in blood flow in ischemic flaps treated with PDRN, with a complete recovery starting from day 5 (ischemic flap + vehicle, 1.80 ± 0.25; ischemic flap + PDRN, 2.46 ± 0.25; P < .001). Administration of PDRN enhanced the expression of VEGF (ischemic flap + vehicle, 5.3 ± 0.6; ischemic flap + PDRN, 6.2 ± 0.5; P < .01) at day 5, and iNOS (ischemic flap + vehicle, 3.9 ± 0.6; ischemic flap + PDRN, 5.3 ± 1; P < .01), but reduced HIF-1α expression (ischemic flap + vehicle, 7 ± 1.1; ischemic flap + PDRN, 4.8 ± 0.5; P < .05) at day 3. Histologically, the PDRN-treated group showed complete re-epithelialization and well-formed granulation tissue rich in fibroblasts.

CONCLUSIONS

These results suggest that PDRN restores blood flow and tissue architecture, probably by modulating HIF-1α and VEGF expression, and may be an effective therapeutic approach in improving healing of ischemic skin flaps.

The effects of vitamin E and selenium on blood flow to experimental skin burns in rats using the 133Xe clearance technique

The aim of the present experimental study was to determine and to compare the effects of vitamin E and of selenium on the blood flow to a wound region in rats, using the xenon-133 (133Xe) clearance technique. Burn wounds were made on the right thighs of rats followed by oral administration of vitamin E or selenium for a period of 10 days. The effect of vitamin E and of selenium individually on blood flow in the wound region was assessed before and after oral administration using the 133Xe clearance technique. Both vitamin E and selenium significantly increased the blood flow in the wound region (P<0.05). Our results in rats suggest that both vitamin E and selenium have beneficial effects on the skin wound healing process by increasing the skin blood flow.

Models to study ischemia in chronic wounds

Wound healing is a complex immune response designed to achieve tissue repair following injury. Imbalance of stimulating and inhibiting factors cause failure of healing. Ischemia is a major cause of wound repair dysregulation and may be limb and life threatening. Investigating ischemic wound healing using animal models minimizes the complex accompanying factors that are usually present in humans, such as age or diabetes. This paper presents a limited review on normal physiological healing and on models that are used to study compromised healing under ischemic conditions.

RECOMBINANT HUMAN ERYTHROPOIETIN STIMULATES ANGIOGENESIS AND HEALING OF ISCHEMIC SKIN WOUNDS

Wound healing in ischemic tissues such as flap margins due to inadequate blood supply is still a source of considerable morbidity in surgical practice. Adequate tissue perfusion is particularly important in wound healing. We investigated the effects of recombinant human erythropoietin (rHuEPO) on wound healing in an ischemic skin wound model. Sixty-three Sprague-Dawley rats were used. Normal incisional wound and H-shaped double flaps were used as the wound models. Animals were treated with rHuEPO (400 IU/kg) or its vehicle. Rats were killed on different days (3, 5, and 10 days after skin injury) and the wounded skin tissues were used for immunohistochemistry and for analysis of vascular endothelial growth factor content and collagen content. Tissue transglutaminase immunostaining of histological specimens was used as a vascular marker to determine the level of microvessel density. The results showed a higher level of vascular endothelial growth factor protein and an increased microvessel density in ischemic wounds with rHuEPO treatment than the normal incisional wounds and ischemic control wounds. Collagen content was higher in the incisional wounds and in the ischemic wounds with rHuEPO treatment compared with the ischemic control wounds. Our results suggest that erythropoietin may be an effective therapeutic approach in improving healing in ischemic skin wounds.

Microcirculatory hemodynamics of the rat cremaster muscle flap in reduced blood flow states

Recent studies revealed that muscle and musculocutaneous flaps have the lowest peripheral resistance and best flap survival. The critical values of flow rates responsible for this survival have not been established. The authors evaluated the effect of prolonged arterial flow reduction on flow hemodynamics and muscle flap survival, independent of neovascularization using the rat cremaster muscle island flap model for microcirculatory studies. Muscle flaps were implanted into a transparent Plexiglas chamber to allow prolonged observation of the microcirculation. Twenty-six male Sprague-Dawley rats were studied in three experimental groups. In group I (control; no occlusion), after flap isolation, the cremaster muscle was implanted into the tissue chamber and microcirculatory measurements were performed from day 0 to day 3. In group II, after flap isolation, flow in the main feeding artery (the iliac) was reduced with a silk suture loop between 47% and 62%. In group III, arterial flow was reduced between 63% and 80%. Vessel diameters, red blood cell velocities, number of perfused capillaries, and number of rolling, sticking, and transmigrating leukocytes were reduced daily for each rat. Immediately after flow reduction, mean arteriolar (A1) diameters were significantly smaller in group II (25%) and group III (29%) compared with the controls (p<0.05). This reduction was confirmed by a drop in red blood cell velocities of 37% and 58% in groups II and III respectively (p<0.05). At day 1, more than 60% of group III flaps had no arterial flow, whereas normal flow was observed in control flaps for as long as 3 days. In addition, the number of perfused capillaries dropped significantly (by 42%) in group II flaps after 3 days (p<0.05). The authors conclude that continuous arterial blood flow reduction exceeding 60% of the normal volume, independent of angiogenesis, is incompatible with flap viability in the rat cremaster muscle model.

The effect of vascular endothelial growth factor on the healing of ischaemic skin wounds

The effect of exogenous vascular endothelium growth factor (VEGF) on wound healing in an ischaemic skin flap model was evaluated in this study. Seventy-two Sprague-Dawley rats were used. Normal incisional wound and H-shaped double flaps were used as the wound models. The study was divided into two parts. In Part I, VEGF protein levels were determined from the incisional and H-shaped ischaemic wounds at 12 and 24 h, postoperatively. In Part II, tensile strength and immunohistochemical stains were examined to determine the level of microvessel density (MVD) at 1 and 2 weeks, postoperatively in simple incisional wounds, ischaemic wounds, and ischaemic wounds following 1 ml (1 microg/ml) exogenous VEGF injections into the subcutaneous tissue. The results showed a significantly higher level of VEGF protein in the ischaemic wounds than the incisional wounds. Tensile strength was statistically higher in the incisional wound group and in the ischaemic flap wounds with VEGF treatment compared to the ischaemic flaps with no treatment at 1 week, postoperatively (p>0.05). MVD data indicated that ischaemic wound repair with VEGF treatment had significantly higher MVD than the normal incisional wounds and ischaemic wounds without treatment. We conclude that exogenous application of VEGF can increase early angiogenesis and tensile strength in the ischaemic wound.

Thrombin peptide TP508 accelerates closure of dermal excisions in animal tissue with surgically induced ischemia

TP508 is a synthetic peptide corresponding to amino acids 508 through 530 of human prothrombin. We previously demonstrated that a single topical application of TP508 stimulates revascularization and healing of acute incisional and excisional wounds in normal, healthy rat skin. To determine if TP508 would enhance wound healing in ischemic skin, we used bipedicle flaps, cranially based flaps, and free grafts to surgically create ischemic regions on the backs of rats. Full-thickness, circular excisions were made within the flaps or grafts and immediately treated with a single application of saline +/- TP508 (0.1 microg/wound). Compared to wound closure in normal skin, ischemic skin wounds exhibited delayed closure, and the length of delay correlated with the degree of surgically induced ischemia. TP508 significantly accelerated closure in both normal and ischemic skin, resulting in closure rates that were increased within the first 7 days of wounding by 30% in normal tissue and bipedicle flaps, 50% in cranially based flaps, and 225% in free grafts. Moreover, in both flap models, TP508 restored the rate of closure to a rate approximating the control rate observed in normal skin. Histological comparisons of wound tissue from normal skin and cranially based flaps showed that ischemia reduced early recruitment of inflammatory cells at day 1 but increased inflammatory cell numbers in wound beds at day 14. TP508 treatment of ischemic flap wounds significantly increased early inflammatory cell recruitment and restored the normal rapid resolution of the inflammatory phase. In addition, at day 7, TP508-treated wounds appeared to have an increased number of large functional blood vessels compared to saline controls. These studies support the potential efficacy of TP508 in treating ischemic wounds in humans.

Cardiovascular disease and treatment outcomes with osseointegration surgery

STATEMENT OF PROBLEM

The frequency of prescription of implant-supported prostheses demands increased scrutiny of systemic health condition on treatment inclusion and exclusion criteria. The risks of an impaired healing response in patients with certain types of cardiovascular diseases (CVD) suggest a possible risk for implant failure in such patients.

PURPOSE

This preliminary study surveyed implant treatment outcome of patients with cardiovascular diseases.

METHODS

A retrospective analysis of 246 consecutively treated patients was conducted. The patients comprised a CVD interest group of 39 patients, and control subgroups of 98 healthy and 109 patients with a history of other systemic disease.

RESULTS

Differences in implant failure rates between the groups were not found to be significant. Though the sample size is small, these results suggest that CVD may not be a risk factor for successful osseointegration.

The influence of occlusive dressing and hyperbaric oxygen on flap survival and the healing of ischaemic wounds

The effect of dressing with Duoderm (hydrocolloid) and treatment with hyperbaric oxygen was investigated on the healing of ischaemic incisional wounds and on flap survival in rats. After 10 days, Duoderm dressing of ischaemic wounds decreased all strength parameters (load*S, stress*S) by 41%-44% and the improvement of ischaemic wound healing by hyperbaric oxygen treatment shown in our previous study was not seen. After removal of Duoderm on day 10 the biomechanical properties had improved but not returned to normal on day 20. In the dressed animals the shrinkage of ischaemic wounds and the extension of necrosis on the ischaemic flaps were reduced. Dressing may be useful clinically in preventing superficial dermal necroses. One must, however, be aware of the impairment of the wound strength of the incisional wounds.

The effect of recombinant basic fibroblast growth factor (bFGF) in fibrin adhesive vehicle on the healing of ischaemic and normal incisional skin wounds

Normal and ischaemic incisional wounds in rats were treated with recombinant human basic fibroblast growth factor (rbFGF) in fibrin adhesive vehicle. After 10 days of healing the maximum load*S and stress*S (S denotes correction for shrinkage) of ischaemic wounds were increased by 45% and 39%, respectively, after treatment with 20 micrograms rbFGF and by 67% and 56% after treatment with 60 micrograms rbFGF. After 20 days only 20 micrograms rbFGF had any effect and increased maximum load*S by 31% and energy at maximum (load*S, stress*S) by 40%-48%. In normal wounds 0.6-20 micrograms and 60 micrograms rbFGF decreased the strength parameters by 19%-34% and 49%-52%, respectively, after 10 days. After 20 days there was no negative influence but 60 micrograms rbFGF increased the biomechanical properties by 15%-24%. Treatment with the fibrin adhesive vehicle alone decreased the biomechanical properties of ischaemic wounds after 20 days, and of normal wounds after both 10 and 20 days. In conclusion, rbFGF can improve the healing of ischaemic wounds and may be used in the treatment of ischaemic wounds in patients, but it can have negative effects on normal wound healing.

Diclofenac and indomethacin influence the healing of normal and ischaemic incisional wounds in skin

The influence of diclofenac and indomethacin on the healing of normal (non-ischaemic) incisional wounds, and of ischaemic incisional wounds using a flap model, was studied in 192 rats. Both drugs improved the strength of normal wounds as the energies at maximum load and stress increased by 23% - 33% after 10 days. After 20 days the treated normal wounds were stiffer. In ischaemic wounds neither drug influenced the biomechanical properties after 10 days, which reflects the healing of the deep dermis, but both countered the ischaemia of the superficial skin as the necroses on the skin flaps decreased. After 20 days the drugs decreased some of the strength parameters of ischaemic wounds, indomethacin in particular, which decreased these parameters by about 20% - 35%. In conclusion, in certain doses the drugs improved the healing of normal wounds. The healing of ischaemic wounds was unaffected after 10 days but decreased after 20 days. The drugs may, however, be used for reducing superficial necroses of skin flaps.

Effect of delayed primary closure on the healing of ischemic wounds

OBJECTIVE

To study the influence of delayed primary closure on the healing of ischemic wounds in rats.

METHODS

Wounds sutured after a delay of 3 days were compared with primary closed wounds by biomechanical testing.

RESULTS

The delayed wounds were as strong as primary closed wounds when tested 10 days after wounding. Thirteen days after wounding (10 days after closure), nearly all the biomechanical parameters of the delayed wounds were increased, compared with those of primary closed wounds that had healed for 10 days. The wounds closed after a delay were weaker, however, when tested 20 days after wounding.

CONCLUSION

An ischemic wound can safely be left open for 3 days before suturing, i.e., for prevention of infection in contaminated wounds, without affecting the biomechanical properties at the time of removing the sutures, which is often performed clinically 10 to 12 days after the operation.

The impact of ischemia on wound healing is increased in old age but can be countered by hyperbaric oxygen therapy

The healing of normal incisional wounds and ischemic flap wounds was investigated in young (10 weeks) and old (102-104 weeks) rats, together with the effect of treatment with hyperbaric oxygen on day 0-3 of healing. After 10 days of healing all biomechanical strength parameters of normal wounds were decreased by 30-40% and of ischemic wounds by 40-51% in the old animals compared with the young controls. After 20 days all strength parameters of normal wounds and ischemic wounds were decreased by 29-37% and 46-58%, respectively, in the old rats compared with those of the young ones. Treatment with hyperbaric oxygen of ischemic wounds in old animals increased all strength parameters by 36-50% after 10 days and by 67-88% after 20 days. For young animals, the corresponding increase was only 21-35% after 10 days and no effect was seen after 20 days. The shrinkage of ischemic wounds was decreased by 48% in the old animals compared with the young ones. It can be concluded that ischemia intensifies the impairment of the healing seen in old age. On the other hand, treatment of ischemia with hyperbaric oxygen is much more effective in old animals, despite the fact that it also has a pronounced effect in young animals. Furthermore, the results suggest a decreased wound contraction with age.

Failure of buflomedil to improve wound healing in ischaemic skin flaps

The effect of buflomedil and isoxsuprine on the healing of ischaemic wounds was investigated using an ischaemic flap model previously evaluated on rats. The drugs were given twice daily intraperitoneally for a total of nine days starting on the day before operation. The wounds were tested biomechanically after 10 and 20 days of healing, respectively, and the length of surface necrosis on the flaps was measured after 10 days. The study showed no differences in any of the biomechanical (functional) parameters of the ischaemic wounds compared with the control groups, either after 10 or 20 days of healing. There were no differences in the length of surface necrosis on the flaps. Neither of these drugs has so far convincingly proved to be effective in the treatment of ischaemic wounds or flaps.

Effect of photodynamic therapy on the healing of a rat skin flap and its implication for head and neck reconstructive surgery

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) may as adjuvant therapy by used to reduce tumor recurrence in the head and neck with surgery, given intraoperatively after resection. A concern with the use of intraoperative PDT is the possible effect on wound healing, especially on the healing of myocutaneous skin flaps, which are widely used to reconstruct defects following resections for head and neck cancer. STUDY DESIGN/ MATERIALS AND METHODS: A flap, based on the inferior epigastric artery, was prepared in thirty male Lewis rats. Group I did not receive any further treatment but the wound was left open for 20 minutes. Group II was injected with 5mg/kg Photofrin, 48 hours prior to the operation and also did not receive any further treatment. The wound bed and wound borders of group III were treated with 630nm light of different dosages, delivered by an argon dye laser. Animals in group IV received 5mg/kg Photofrin 48 hours prior to the operation and their wound beds were treated with the same light dosages as group III. After the treatment all flaps were replaced into the wound bed and the incisions were closed. Biopsies for histological analysis were taken at several time points; and on day 21, biopsies for wound tensile strength measurements were taken.

RESULTS

The wound healing in group I, II, and III appeared normal and there were no differences seen between these groups. Also, the tensile strength did not differ significantly. The flaps of group IV showed serous effusion, epidermal necrosis, and weaker tensile strength (P = .04 and .02 for the light doses of 50 J/sq cm and 75 J/sq cm respectively) at a specific time point.

CONCLUSION

The results of this study demonstrate that PDT given immediately before flap reconstruction will result in delayed wound healing. These results should be considered when contemplating the use of PDT as adjuvant intraoperative therapy for tumor surgery requiring flap reconstruction after ablative surgery.

The effect of hyperbaric oxygen on different phases of healing of ischaemic flap wounds and incisional wounds in skin

Several studies have revealed a positive effect of treatment of ischaemic wounds and flaps with hyperbaric oxygen. We studied the effect of 100% oxygen (2.4 ATA) for 90 min daily on different phases of healing ischaemic and normal incisional wounds in rats. Hyperbaric oxygen on day 0-3 significantly increased almost all the force parameters of ischaemic flap wounds by 41-57% after 10 days of healing. On the other hand, when the treatment was continued until day 9 the positive effect on the wound healing was abolished. Furthermore, when hyperbaric oxygen was given on days 4-9 there was a tendency towards a decrease in the biomechanical parameters. Hyperbaric oxygen had no effect on the healing of normal incisional wounds.

Ischemia in wound healing. II: Design of a flap model--biomechanical properties

A standardized reproducible H-shaped double flap model for biomechanical testing of ischemic wounds was developed in rats. After 10 days of healing all the biomechanical parameters of the flap wounds decreased significantly, compared with normal healing incisional wounds. After 20 days of healing the extensibility as well as the most important biomechanical parameters were still significantly decreased. In part I of this study we showed that on day 1 the blood flow had decreased to 7% of the flow in normal incisional wounds, though it returned to normal on day 16. Here we show that this drop in blood flow results in a significant decrease in all the biomechanical parameters and thereby caused significant delay in the healing of the test wounds. There was no correlation between any of the biomechanical parameters and the length of surface necrosis on the flaps. These necroses thus do not necessarily reflect necrosis of the dermis, where the healing is responsible for the continuity and strength of the skin.

The influence of age on the healing of normal and ischemic incisional skin wounds

Experimental studies have not shown that the 'common' clinical experience, which suggests that wound healing is impaired in an old organism, is valid for healthy old experimental animals. We have developed a model in the rat for ischemic wound healing by using an H-shaped double skin flap, where the test wound is the horizontal line in the H. Our previous studies have shown that the blood flow in this wound is only 7% of that of a normally vascularized wound on the first postoperative day. Functional (biomechanical) properties of this wound are decreased by up to 67% after 10 days of healing and certain key properties by up to 64% after both 10 and 20 days. This study reports on the effect of aging, using 3- and 24-month-old rats. The 'normal' incisional wounds healed equally well in both groups. On the other hand, the ischemic wounds in the old animals were found to be impaired by 40-65% compared to similar wounds in the young animals. It is concluded that ischemia is deleterious for wound healing in old age and that one of the key elements of the clinical experience of impaired wound healing in old age is probably based on concomitant diseases in old patients, contributing to varying degrees of ischemia in the traumatized tissue.