Regional variations of laser Doppler blood flow in ischemic skin flaps

An island skin flap was designed on the left inferior epigastric neurovascular bundle of anesthetized male rats. Blood flow was measured in situ with a laser Doppler flowmeter at 20 discrete points on a grid system (5 points in each quadrant of the flap) before and after surgery, or before vascular occlusion, during reperfusion, and 48 to 72 hours later. Two series of experiments were performed. In the first series, the raised flap was placed in a bath containing heated Ringer's solution and the left pedicle was cross-clamped. After 30 minutes, adenosine at a concentration that produced supramaximal vasodilatation, or its vehicle, was added to the bath. After 1 hour total occlusion time, the vascular clamp was released and adenosine treatment was continued for the first 30 minutes of reperfusion. In the second series, the protocol was similar except that adenosine, or its vehicle, was infused into the ischemic flap by means of the distal stump of the right inferior epigastric artery. After 48 to 72 hours, fluorescein was injected IV. The data showed a significant regional variation in baseline laser Doppler blood flow that was further altered by surgically raising the flap. Whereas proximal axial laser Doppler blood flow was essentially unchanged from the preoperative baseline, distal axial laser Doppler blood flow decreased 10 to 50 percent, and proximal and distal dependent laser Doppler blood flow decreased 50 to 80 percent. Thus no single value accurately reflected total flap perfusion. Necrosis occurred only in the dependent flap regions, which confirmed previous work. In the dependent regions, especially along the incision line, postoperative laser Doppler blood flow was lowest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reverse-flow island sural flap

The reverse flow island sural flap is presented as an alternative to flaps currently used for reconstruction of small and medium substance losses in the distal third of the leg, ankle, and heel. This is a random type of flap, based on the reverse flow of the superficial sural artery, which mainly depends on the anatomy of the perforators of the peroneal artery system.The anatomic structures that constitute the pedicle are the superficial and deep fascias, the sural nerve, the short saphenous vein, and the superficial sural artery. The skin island and the subcutaneous cellular tissue complement the flap proper. This skin island was demarcated at any point of the median or distal thirds of the leg, having the short saphenous vein and the sural nerve on its central axis. The distal dissection limit of the pedicle is located 5 centimeters above the lateral malleolus. This limit is established so as to ensure the integrity of the perforators from the principal arteries of the leg, mainly the peroneal artery, responsible for the reverse flow nourishing the flap. These perforators will affect anastomoses with the superficial sural artery in charge of irrigating the structures compounding the flap.A total of 71 patients were operated on with this technique, some of them with basic pathologic abnormalities limiting the distal blood flow, such as diabetes mellitus, and some others having proven vascular insufficiency or displaying unstable areas attributable to problems such as pseudarthrosis and osteomyelitis, which needed to be covered. Fifteen flaps (21.1 percent) suffered partial necrosis, which did not compromise the final result, and another three (4.2 percent) showed total loss. The flap in question has great mobility and versatility, allowing the treatment of specific areas of the lower limb, without sacrificing important arteries or mobilizing structures that might bring about functional deficits.     

Distally based anterolateral thigh flap: an anatomic and clinical study

The distally based anterolateral thigh flap has been used for coverage of soft-tissue defects of the knee and upper third of the leg. This flap is based on the septocutaneous or musculocutaneous perforators derived from the lateral circumflex femoral system. The purpose of this study was to examine the results of anatomical variations of the descending branch of the lateral circumflex femoral artery and the retrograde blood pressure of the descending branch of the lateral circumflex femoral artery so that the surgical technique for raising and transferring a distally based anterolateral thigh flap to the knee region could be improved. The authors have actually used this flap in three cases. In 11 thighs of six cadavers, the descending branch of the lateral circumflex femoral artery had a rather consistent connection with the lateral superior genicular artery or profunda femoral artery in the knee region. The pivot point, located at the distal portion of the vastus lateralis muscle, ranges from 3 to 10 cm above the knee. In their three cases, the maximal flap size was 7.0 x 16.0 cm and was harvested safely, without marginal necrosis. The mean pedicle length was 15.2 +/- 0.7 cm (range, 14.5 to 16 cm). The average proximal and distal retrograde blood pressure of the descending branch of the lateral circumflex femoral artery was also studied in another 11 patients, and the anterolateral thigh flap being used for reconstruction of head and neck defects showed 58.3 and 77.7 percent of proximal antegrade blood pressure, respectively. The advantages of this flap include a long pedicle length, a sufficient tissue supply, possible combination with fascia lata for tendon reconstruction, and favorable donor-site selection, without sacrifice of major vessels or muscles.     

Cyclic GMP-dependent and cyclic AMP-dependent protein kinases, protein kinase modulators and phosphodiesterases in arteries and veins of dogs. Distribution and effects of arteriovenous fistula and arterial occlusion.

Possible involvement of cyclic GMP-dependent and cyclic AMP-dependent protein kinases, protein kinase modulators and cyclic nucleotide phosphodiesterases in functions of vascular tissues were investigated in the dog. All of the above activities, localized in the smooth muscle-rich inner layer of the blood vessels, were found to be higher in the arteries than in the veins. The peripheral arteries were disproportionately richer in cyclic GMP-dependent protein kinase (as indicated by high ratios of cyclic GMP-dependent to cyclic AMP-dependent protein kinase) than were the veins, with the exception of the pulmonary artery, an atypical arterial tissue exposed to low blood pressure. Interestingly, the protein kinase ratio for the aorta, an artery with no significant role in blood pressure regulation, was not higher than that for the vena cava. Creation of femoral arteriovenous fistulae in the dogs led to preferential reductions in the cyclic GMP-dependent enzyme activity both in the proximal and distal arteries, whereas it was elevated in the stressed vein distal to the anastomotic site. The cyclic GMP-dependent enzyme was preferentially reduced in the saphenous artery distal to occlusion. Changes in the cyclic GMP-dependent enzyme activity appeared to precede gross atrophy or hypertrophy of the vessels. It is suggested that the vascular cyclic GMP-dependent protein kinase may be closely related to peripheral resistance and its regulation.     

Cyclic GMP-dependent and cyclic AMP-dependent protein kinases,protein kinase modulators and phosphodieterases in arteries and veins of dogs Distribution and effects of arteriovenous fistula and arterial occlusion

Possible involvement of cyclic GMP-dependent and cyclic AMP-dependent protein kinases, protein kinase modulators and cyclic nucleotide phosphodiesterases in functions of vascular tissues were investigated in the dog. All of the above activities, localized in the smooth muscle-rich inner layer of the blood vessels, were found to be higher in the arteries than in the veins. The peripheral arteries were disproportionately richer in cyclic GMP-dependent protein kinase (as indicated by high ratios of cyclic GMP-dependent to cyclic AMP-dependent protein kinase) than were the veins, with the exception of the pulmonary artery, an atypical arterial tissue exposed to low blood pressure. Interestingly, the protein kinase ratio for the aorta, an artery with no significant role in blood pressure regulation, was not higher than that for the vena cava. Creation of femoral arteriovenous fistulae in the dogs led to preferential reductions in the cyclic GMP-dependent enzyme activity both in the proximal and distal arteries, whereas it was elevated in the stressed vein distal to the anastomotic site. The cyclic GMP-dependent enzyme was preferentially reduced in the saphenous artery distal to occlusion. Changes in the cyclic GMP-dependent enzyme activity appeared to precede gross atrophy or hypertrophy of the vessels. It is suggested that the vascular cyclic GMP-dependent protein kinase may be closely related to peripheral resistance and its regulation.     

Use of a modified oxygen microelectrode and laser-Doppler flowmetry to monitor changes in oxygen tension and microcirculation in a flap

Flap failure is a clinical problem in free tissue transfer, and there is no reliable device for monitoring the tissue. Differentiating between an arterial occlusion and venous congestion is also a problem. A study was undertaken to monitor viability in a pedicled groin flap and to compare two different monitoring methods. The oxygen tension in the flap, measured with a modified Clark-type microelectrode (tip diameter = 3 to 8 microm; 90 percent response within 2.6 +/- 0.5 seconds), was compared with changes in blood flow in the flap, measured with a laser-Doppler probe. In 11 Sprague-Dawley rats, the changes in oxygen tension and blood flow in the pedicled groin flap were studied after clamping and subsequent reperfusion of the artery or vein. After occlusion of the artery to the flap, oxygen tension decreased to a stable value (i.e., the recording level remained unchanged for 30 seconds), from 19.7 +/- 1.8 to 0.3 +/- 0.1 mmHg, after 193 +/-25 seconds; blood flow decreased to a stable value, from 117 +/- 21 to 54 +/- 18 perfusion units, after 26 +/- 6 seconds. Clamping of the vein resulted in a decrease in oxygen tension, from 17.1 +/- 1.8 to 1.4 +/- 0.7 mmHg, after 416 +/- 67 seconds, and blood flow decreased to a stable value, from 90 +/- 14 to 35 +/- 6 perfusion units, after 107 +/- 27 seconds. The results of this study show that there is a difference in oxygen tension and blood flow responses between arterial and venous occlusion and that it may be possible with both methods to distinguish arterial from venous occlusion. However, although oxygen tension measurements are slightly slower in response than laser-Doppler measurements, the values are more reliable as a diagnostic tool for interpretation of a vessel occlusion.     

Survival and blood flow evaluation of canine venous flaps

Using a canine model, we compared postoperative viability of saphenous venous flaps, cephalic venous flaps, and composite-tissue grafts without vascular connections. Of the saphenous flaps, 14 percent survived. Of the flaps based on the cephalic vein, 75 percent survived. Cephalic composite-tissue grafts were 13 percent successful. The presence of a more intricate venous plexus in a flap seems to increase its chances of success. Arterial injections of radioisotope-labeled microspheres were used to chart revascularization in cephalic flaps. These flaps demonstrated arterial blood flow by day 3, while the composite grafts showed no flow until day 7. Venous injections of microspheres distal to the flap were used to test vein-to-capillary blood flow. No significant entrapment of microspheres within the flaps occurred at any time, suggesting such flow to be inadequate.     

The nutrient flap: a new concept of the role of the flap and application to the salvage of arteriosclerotic lower limbs

The nutrient flap is a new concept of the role of the flap. It has three functions: (1) it provides supplementary blood flow to ischemic zones, (2) it assists venous drainage in regions of venous insufficiency, and (3) it induces the formation of a capillary network. Its skin covering role is only accessory. We have applied this principle to osteitis, pseudoarthrosis, and arteriosclerosis. The nutrient flap constitutes a new type of treatment for stage IV arteriosclerosis of the lower limbs when classical revascularization techniques cannot be performed and when high amputation is indicated. Four clinical cases and the surgical techniques used are described. The flap, usually raised from the latissimus dorsi, is anastomosed to the popliteal artery by means of an inverted saphenous vein graft. It is applied to the distal extremity of the limb after excision of the necrotic tissues. The nutrient flap preserves weight-bearing by maintaining the heel.     

Electromagnetic flowmetry--an experimental method for continuous blood flow measurement using a new island flap model

We describe a reliable experimental method for direct, continuous measurement of the rate of blood flow in an island skin flap, using an electromagnetic flowmeter applied to the artery of the flap. The canine saphenous island flap model, developed as part of this study, is a large (11 x 14 cm) island flap, based solely on the saphenous artery (2 mm in diameter). We describe the anatomy of the flap and the method of raising it. Electromagnetic flowmetry is the only method of blood flow determination that provides immediate, continuous, and quantitative measurement of flow. We describe the principles and pitfalls of the electromagnetic flowmeter and the numerous rules of practice that must be observed to obtain consistent results. A validation study was carried out, in which we simultaneously measured arterial inflow with the flowmeter and venous outflow from the flap using direct collection. This study was based on the assumption that at any point in time the arterial and venous rate of flow were equal. We present the results of the study, which show an extremely close linear relationship between the measured and actual rates of flow. We intend to use this experimental method to study the factors that affect the rate of blood flow in free skin flap transfer.     

Functional arterio-venous anastomoses between the testicular artery and the pampiniform plexus in the spermatic cord of rams

Blood flow to the testis, haemoglobin oxygen saturation and testosterone concentration in arterial and venous testicular blood vessels were studied in Texel rams in the breeding and non-breeding season. Blood flow in the proximal and distal testicular artery was measured electromagnetically. The mean flow in the proximal testicular artery was 18.5 ml/min and in the distal testicular artery 7.5 ml/min, and there was no detectable seasonal influence. Haemoglobin oxygen saturation and testosterone concentration were measured in the saphenous artery and vein, the distal testicular artery and vein, and in the proximal testicular vein. The haemoglobin oxygen saturation in the proximal testicular vein was significantly higher than in the distal testicular vein in both seasons. The mean testosterone concentration was significantly lower in the proximal testicular vein than in the distal testicular vein in both seasons. Based on haemoglobin oxygen saturation and testosterone data, it was calculated that between 28 and 46% of the testicular arterial blood was bypassing the testis and was directly flowing through arterio-venous anastomoses towards the pampiniform plexus in the spermatic cord of conscious rams. In anaesthetized rams 55 and 64% of the blood was flowing directly from the testicular artery to the pampiniform plexus based on blood flow data. Transfer of testosterone and oxygen by passive diffusion from the testicular artery to the pampiniform plexus and vice versa in the spermatic cord was not detected.     

Distally based vastus lateralis muscle flap for coverage of wounds about the knee

The blood supply to the vastus lateralis muscle has been evaluated by dye injection techniques in fresh cadaver dissections. The main dominant blood supply is the descending branch of the lateral femoral circumflex artery. Vascular contributions from distal perforators of the superficial femoral artery, the superior geniculate artery, fill the main vascular pedicle in a retrograde fashion. Latex staining is observed consistently in the proximal third of the muscle. Five patients are presented in whom the distally based vastus lateralis muscle flap was successfully used to cover defects above the knee. Superficial muscle necrosis is a complication of this operation but has not precluded its usefulness. It is anticipated that this flap will be useful in the armamentarium of reconstructive surgeons treating such problematic patients.     

Collateral sources of costal and crural diaphragmatic blood flow

We measured the contribution of aortic, internal mammary, and intercostal arteries to the blood flow to the costal and crural segments of the diaphragm and other respiratory muscles in seven dogs breathing against a fixed inspiratory elastic load. We used radiolabeled microspheres to measure the blood flow with control circulation, occlusion of the aorta distal to the left subclavian artery, combined occlusion of the aorta and both internal mammary arteries, and occlusion of internal mammary arteries alone. With occlusion of the aorta distal to the left subclavian artery, blood flow to the crural diaphragm decreased from 40.3 to 23.5 ml . min-1 X 100 g-1, whereas costal flow did not change significantly (from 41.7 to 38.1 ml . min-1 . 100 g-1). Blood flows to the sternomastoid and scalene muscles (above the occlusion) increased by 200 and 340%, respectively, whereas flows to the other respiratory muscles did not change significantly. Blood flows to organs above the occlusion either remained unchanged or increased, whereas flows to those below the occlusion all decreased. When the internal mammary artery was also occluded, flows to the crural segment decreased further to 12.1 and costal flow decreased to 20.4 ml X min-1 X 100 g-1. Internal mammary arterial occlusion alone in two dogs had no effect on diaphragmatic flow. In conclusion, intercostal collateral vessels are capable of supplying a significant proportion of blood flow to both segments of the diaphragm but the costal segment is better served than the crural segment.     

Intraoperative physiologic blood flow studies in the TRAM flap.

An intraoperative study was done to establish the functional and quantitative properties of the blood supply to the TRAM flap through the assessment and manipulation of blood flow through the deep epigastric arterial system. Seventeen patients undergoing unilateral postmastectomy breast reconstruction with lower transverse rectus abdominis myocutaneous (TRAM) flaps were studied. The study is divided into two parts: (1) ultrasonic measurement of blood flow in the deep inferior epigastric artery (DIEA), and (2) direct measurement of blood pressure in the deep epigastric arterial system, after division of the deep inferior epigastric artery. With occlusion of the superior epigastric artery at the level of the upper edge of the skin flap, 71 percent of the patients had a decrease in the blood flow through the deep inferior epigastric artery, with an average decrease of 23 percent. This implies that the area of watershed perfusion in the lower TRAM flap is superior to the umbilicus, and therefore, survival of all lower TRAM flap tissues requires reversal in the normal direction of arterial flow to the flap. The blood pressure in the proximal stump of the deep inferior epigastric arterial system averaged 46 percent of the mean systemic blood pressure. Occlusion of the medial and lateral thirds of the isolated rectus muscle decreased the mean arterial blood pressure in the flap an average of 19 percent in 80 percent of the individuals studied. These data support the technique of harvesting the entire rectus muscle, avoiding muscle-splitting maneuvers that may compromise axial blood flow.     

Increase in the sensitivity of the vascular smooth muscle to constrictor factors after denervation and with a decrease in blood pressure

The effect of denervation on the contractile activity of the saphenous artery in normotensive rats and rats with regional hypotension was studied. Hypotension was caused by partial occlusion of the abdominal aorta distally from the renal arteries, and then, in four weeks, to denervate the saphenous artery, a portion of the femoral nerve in one of the limbs was resected. In two more weeks, the contractile responses of ring preparations of the saphenous artery (after removal of the endothelium and block of neuronal uptake and β-adrenoreceptors) were investigated under isometric conditions. In normotensive rats, the denervation led to an increase in the vascular sensitivity to norepinephrine, phenylephrine, serotonin, and KCl. Similar changes in contraction were caused by chronic hypotension; however, rats with hypotension exhibited no additional denervation-induced increase in the vascular sensitivity. After treatment with glyoxylic acid, the fluorescence intensity of the vascular adrenergic fibers adapted to a reduced pressure was lower than that in the norm. It was assumed that the vascular hypersensitivity in hypotension is caused by impairment of sympathetic innervation.     

Color Doppler flow imaging of the facial artery and vein

The purpose of this study was to provide some guidelines with respect to the location of the facial vessels, display the potential inverted blood flow of the facial artery, and reemphasize the value of color Doppler ultrasound studies in flap planning. An anatomic study of the facial artery and vein was done using color Doppler ultrasonography in 12 adults. The artery and the vein were located together at the lower border of the mandible. Around the oral commissure and under the nasal ala, they were located apart from each other with variable distances. This divergence of the facial vein from the artery is important information in the planning of axial pattern flaps. Furthermore, the reverse flow was observed in 12 patients after the blood flow of the facial artery was stopped by applying pressure manually at the lower border of the mandible. Observation of the reversed flow confirms the possibility of safe elevation of a retrograde flow-arterialized flap based on the distal portion of the facial artery.     

Gore-Tex small-vessel angioplasty: A suitable substitute for the use of autogenous saphenous vein grafts

Autogenous saphenous vein has been the material of choice for small-vessel angioplasty and for circulatory access graft reconstruction. In an effort to conserve autogenous saphenous vein, we used expanded polytetrafluoroethylene (PTFE) grafts in 45 patients over a 12-month period. We used Gore-Tex(*) to reconstruct 17 circulatory access grafts, 16 carotid arteries, two brachial arteries, seven femoral arteries, and three popliteal anterior or posterior tibial arteries. The indications for reconstruction were chronic occlusion of the access grafts, trauma to the brachial and anterior tibial arteries, and atherosclerotic disease of the carotid, femoral, and popliteal-tibial arteries. Of the reconstructed circulatory access grafts, one failed immediately because of technical problems in the conduit, and one failed 11 months after reconstruction. All other grafts have functioned well and have produced a marked improvement in flow. Of the 28 patients who underwent reconstruction of arteries measuring 3 mm or less, two had patent arteries but died shortly after operation. The remaining 26 have been followed for one to 43 months. All reconstructed arteries are patent, and there have been no instances of distal embolization or false aneurysm formation. From this brief experience, we conclude that Gore-Tex is a suitable short-term alternative to saphenous vein for small vessel arterioplasty; it also may be the material of choice for reconstructing the outflow tract of occluded access grafts.     

The vascular supply of the extended tensor fasciae latae flap: how far can the skin paddle extend?

The vascular supply of the tensor fasciae latae flap and of the lateral thigh skin was studied in 10 cadavers to evaluate whether the lateral thigh skin toward the knee could be incorporated into an extended tensor fasciae latae flap. Within each cadaver, vascular injection of radiopaque material preceded flap elevation in one limb and followed flap elevation in the contralateral limb. Flaps raised after vascular injection were examined radiographically to evaluate the vascular anatomy of the lateral thigh skin independent of flap elevation. When vascular injection was made into the profunda femoris, the upper two-thirds of the flaps was better visualized than the distal third. When the injection was made into the popliteal artery, the vasculature of the distal third of the flaps was better visualized. Flaps raised before vascular injection were examined radiographically to delineate the anatomical territory of the vascular pedicle that had been injected. In these flaps, consistent cutaneous vascular supply was only seen in the skin overlying the tensor fasciae latae muscle, confirming that musculocutaneous perforators are the predominant means by which the pedicle of the tensor fasciae latae flap supplies the skin of the lateral thigh. Extended tensor fasciae latae flaps were elevated bilaterally in one cadaver, and selective methylene blue injections were made into the lateral circumflex femoral artery on one side and into the superior lateral genicular artery on the contralateral side. Methylene blue was observed in the proximal and distal thirds of the skin paddles, respectively, leaving unstained midzones. The vascular network of the lateral thigh skin could be divided into three zones. The lateral circumflex femoral artery and the third perforating branches of the profunda femoris artery perfuse the proximal and middle zones of the lateral thigh skin, respectively. The superior lateral genicular artery branch of the popliteal artery perfuses the distal zone. The middle and distal zones meet 8 to 10 cm above the knee joint, where the skin paddle of the tensor fasciae latae flap becomes unreliable. These data indicate that if the aim is to incorporate the skin over the distal thigh in an extended tensor fasciae latae flap without resorting to free-tissue transfer, then either a carefully planned delay procedure or an additional anastomosis to the superior lateral genicular artery is required.     

The vascularized pig fibula bone flap model: effects of multiple segmental osteotomies on growth and viability

Previous work by this laboratory introduced the pig fibula bone flap as a model for the study of the pathophysiology of vascularized bone flaps. Anatomic and hemodynamic studies demonstrated a significant (p < 0.05) decrease in vascular perfusion after a series of segmental osteotomies and rigid fixation (lag screws and miniplates) in the distal end of the flap, suggesting that blood flow to the distal osteotomized segment of the flap may be impaired. Killing the animals after blood flow studies precluded assessment of the effect of these hemodynamic changes on bone healing. Therefore, the aim of this study was to assess the pig fibula bone flap model with respect to viability, healing, and subsequent growth after multiple segmental osteotomies and rigid fixation to contribute to the understanding of vascularized bone flap pathophysiology. Yorkshire pigs (20 to 25 kg) were used for all experiments. Eight pigs underwent unilateral elevation of a vascularized fibula bone flap, which was osteotomized into three segments and orthotopically rigidly fixed using a 2.4-mm mandibular reconstruction plate. The left fibula remained as the control. Fluorochrome labels were injected to assess bone viability and turnover, and both fibulae were assessed for growth radiologically. The fibulae were harvested 21 days postoperatively (when the animals were killed), and bone healing was assessed histologically and clinically. There were no significant differences in preoperative and postoperative lengths of the osteotomized fibulae compared with the controls, suggesting that there was no impairment of growth potential after multiple segmental osteotomies and rigid fixation. Significant (p < 0.05) bony hypertrophy of the osteotomized fibulae was noted when compared with controls. Mobility was observed in 3 of the 32 osteotomies (9 percent), occurring across one proximal and two distal osteotomies in association with failure of fixation. However, histologic and fluorochrome assessment confirmed the viability of all bone segments, as supported by the presence of tetracycline given 2 days postoperatively. The pig fibula bone flap model is well tolerated by the pig. Multiple segmental osteotomies and rigid fixation, previously associated with a significant decrease in blood flow in the distal segment, did not impair either growth potential, viability, or healing ability. It is suggested that the pig fibula is a suitable model for the study of bone flap pathophysiology.     

Enhanced arteriogenesis in mice overexpressing erythropoietin

After permanent occlusion of the femoral artery, the survival of ischemic limb tissue depends on collateral artery growth (arteriogenesis). In previous work, we have shown that shear stress triggers arteriogenesis. To test whether increased shear stress results in enhanced arteriogenesis, we compared arteriogenesis in transgenic mice overexpressing erythropoietin (EPO), which possessed increased blood viscosity through the higher hematocrit (thereby providing increased shear stress), with wild-type mice. The right femoral artery was occluded proximal to the origin of the arteria poplitea. Distal blood flow was assessed by laser Doppler imaging, and the growth and remodeling of collateral arteries was examined by light and electron microscopy and morphometry. After occlusion of the femoral artery, EPO mice demonstrated enhanced arteriogenesis: their collateral arteries developed a 1.7-fold diameter and a 2-fold wall thickness compared with wild-type. However, the blood flow recovery in EPO mice was markedly retarded. Structural remodeling and growth of collateral arteries was markedly enhanced in EPO mice, presumably as a result of increased blood viscosity and shear stress.     

Early circulatory and metabolic events in island skin flaps of the pig

Circulatory and metabolic skin-flap events were studied prior to and up to 6 hours after elevation of buttock island flaps in pigs. During the elevation, significant reductions in superficial skin blood flow, measured by laser Doppler flowmetry (LDF) and dermal flap temperature, were seen. Significant correlations were found between blood flow and temperature. Total flap blood flow, measured as venous outflow, also showed an initial transient decrease, but 2 hours after flap construction, venous outflow had returned to preoperative values. A significant increase in lactate release, together with increased oxygen consumption and glucose uptake, was seen 4 hours after the surgical intervention. Hypoxanthine release, indicating ischemia, was seen only during the first hour after flap elevation. Noradrenaline outflow was noted after 4 and 6 hours, but there was no parallel reduction in flap blood flow. A great deal of the flow reduction in acutely elevated island flaps may thus be due to primary hypothermia rather than to the degenerative release of noradrenaline, which seems to have no early effect on skin flap blood flow. On the other hand, the noradrenaline release may be linked to an increased metabolic activity in the skin flaps.