The isotope clearance technique for measuring skin blood flow

Metabolism in myocutaneous flaps studied by in situ microdialysis

The aim of this investigation was to follow the metabolism of myocutaneous flaps using microdialysis. After subcutaneous implantation of a microdialysis catheter into the flap tissue, serial samples were collected and changes in composition of the extracellular fluid assessed. Ten women underwent reconstructions with transverse rectus abdominis myocutaneous (TRAM) or latissimus dorsi flaps. Glucose, glycerol, and lactate concentrations were measured in the flaps and compared with those in adipose control tissue located over the hip. A transient rise in glucose was observed initially in the flaps. The glycerol concentration also increased significantly, and remained increased for approximately 12 hours after the operation. The lactate concentration changed in the same direction, but stayed elevated in the flap tissue during the entire investigation (24 hours). Neither of these parameters changed to the same extent in the control tissue. In one of the patients a haematoma developed postoperatively in the flap. This incident was accompanied by a sharp decline in glucose, and marked additional increases in glycerol and lactate concentrations. It may well be that this "metabolic pattern" in flap tissue signals threatening flap ischaemia. If so, this new microdialysis technique may be useful as a postoperative surveillance tool in myocutaneous flap surgery.

Evaluation of lymphatic drainage in free flaps by lymphoscintigraphy: a preliminary study

Lymphatic drainage from free flaps was studied by lymphoscintigraphy in 14 patients in whom free vascularised flaps were used to cover defects caused by trauma or tumour ablation. Lymphoscintigrams were done after intradermal injection of Technetium-99m-Dextran in the flap and in the corresponding contralateral normal area. The retention of radioactivity at the injection sites after 1 h was computed and expressed as percentages of baseline activity at the time of injection. 25 studies were done in 14 patients at intervals varying from 9 days to 6 years postoperatively. In all cases, radioactivity was detected beyond the flaps in the lymphatic channels and draining lymph nodes. There was no significant difference (P = 0.27) between the retention of activity in the flaps (mean 88.68%; s.e.m. 1.25) and that in the corresponding contralateral control area (mean 86.88%; s.e.m. 1.35). This study shows that lymphatic drainage in a free flap is established early after surgery.

On the safety of 5-[125I]iodo-2'-deoxyuridine--Preclinical evaluation in swine

To increase tumor incorporation and minimize hepatic degradation of radio-IUdR, compartmental administration routes are being considered as an alternative to intravenous (i.v.) injections. Although there are significant data on the biodistribution and some reports on radiotoxicity of i.v.-administered 125IUdR, similar results for other routes of delivery are not available. We have undertaken a series of experiments intended to examine radiation effects of 125IUdR after intravesical (3 swine; eight 3 mCi doses at 4-day intervals), intracarotid (3 swine; two 10 mCi doses at 2-week intervals), and intra-aortic (5 swine, single dose of 10 mCi) administration in a swine model. Liver, renal functions, and complete blood counts were monitored throughout the duration of the experiment. Pharmacokinetics, systemic distribution of radioactivity and metabolites were measured. The normal tissue 125IUdR uptake and histology were determined after necropsy. No adverse systemic effects were identified. Clinical observations, laboratory data, and necropsy results were within normal range.

Perfusion imaging of skin island flap blood flow by a scanning laser-Doppler technique

Conventional laser-Doppler perfusion measurements can only obtain information from a single site. Since superficial blood flow is heterogeneous, this is a serious limitation, particularly in studies of methods to improve skin flap survival. A scanning laser-Doppler instrument has been developed which provides both an image and quantitative information about perfusion of the superficial tissue. We have evaluated this instrument in a circumflex iliac artery island flap model in the pig. The validity of the model was demonstrated by fluorescein dye injection and histology. Elevation of flaps was found to increase proximal flap blood flow but to decrease it in the distal portion. In flaps subjected to arterial ischaemia (9 h) and reperfusion we found an early increase in proximal flow, which gradually extended distally over the first 40 to 60 min. 16 h later, flow had declined, compatible with reperfusion damage to the vasculature. We suggest that perfusion imaging may be a valuable technique for investigating the mechanisms and extent of reperfusion injury.

Nonsurgical delay of skin flaps: effect of a suture delay technique on blood flow and survival

Surgical delay is the only clinical means of improving survival of skin flap tissue, but it has inherent risks and costs of a surgical procedure. This study tested the hypothesis that any method of disrupting the circulation at the distal perimeter of a planned skin flap would induce collateral circulation from the base of the flap and thereby improve flap survival. The suture delay technique was performed on rats, and two outcome measures were used: blood flow patterns and skin flap survival. Blood flow patterns were tested before and after the suture technique by means of the base occlusion test. Flap survival in the suture delay group was compared with survival in acute and surgical delay control groups. Flap survival in the suture delay group (95.6% +/- 0.6%, n = 22) was significantly greater than in the acute control group (85.7% +/- 1.6%, n = 22) and was not different from that in the surgical delay model (95.2% +/- 0.5%, n = 21). Laser Doppler studies demonstrated a change in blood flow patterns. This study supports the theory that the mechanism of the delay phenomenon is the development of collateral blood from the base of the flap and suggests that the benefits of delay can be achieved with minimal surgical trauma.

A freeze-injured skin graft model for the quantitative study of basic fibroblast growth factor and other promoters of angiogenesis in wound healing

A new in vivo model has been developed for the quantitative study of promoters and potential promoters of angiogenesis. Full thickness rat skin autografts received a reproducible and uniform freeze injury, before being applied to full thickness wounds, in order to delay revascularisation. Blood flow in the grafts was measured during the healing period using noninvasive (laser Doppler flowmetry) and invasive (133Xe clearance) techniques. The increase in blood flow over a period of 10-14 days was taken as an index of angiogenesis. These measurements were corroborated by histological assessment of the graft vasculature, using a laminin stain to highlight vascular basement membrane. Freeze injury delayed but did not ultimately prevent full graft revascularisation (p < 0.01 for laser Doppler flowmetry and 133Xe clearance). Application of the angiogenic agent basic fibroblast growth factor (bFGF), in slow release pellet form, stimulated angiogenesis in cryoinjured grafts in a dose-related fashion. Doses of 500 and 5000 ng bFGF produced significant stimulation (500 ng bFGF, p < 0.001, and 5000 ng bFGF, p < 0.01, for both laser Doppler flowmetry and 133Xe clearance; increased vessel profile counts, p < 0.05, at each time point tested for both doses) while 50 ng bFGF had no significant effect. By contrast, 500 ng bFGF had no measurable effect on uninjured grafts. In addition, bFGF-stimulated angiogenesis in cryoinjured grafts was antagonised by a neutralising antibody to bFGF, demonstrating the specificity of action of bFGF in this model.

The relationship between regional blood flow and absorption of lignocaine

With the increasing application of certain surgical procedures to 'day surgery' cases, there has been greater utilization of local anaesthetic agents. Such procedures are undertaken using single infiltration dosage recommendations for lignocaine, both with and without adrenaline. The present paper describes results obtained from a sheep model that considers the role of the regional blood flow of the injected site as a determinant of lignocaine absorption and resultant pharmacokinetics. The peak concentration of lignocaine in plasma following administration to two selected sites of different vascularity (as determined by a technetium99 washout method), as well as the effect of concomitant adrenaline administration, was shown to correlate with the regional blood flow to the site (rs = 0.73, P = 0.008). Extrapolating these animal data to the clinical situation suggests that larger dosages of lignocaine could be used safely for infiltration anaesthesia in regions of poor regional blood flow without posing a threat of lignocaine-induced toxicity, and that the current dosage recommendations could be modified in respect of the regional blood flow of the particular site to be infiltrated.

Non-radioactive coloured microsphere measurement of regional tissue blood flow for axial pattern flaps in rabbits

We administered non-radioactive coloured microspheres (NRACM) to measure the regional tissue blood flow (RTBF) of eight axial pattern flaps and four kidneys in four rabbits using four repeated injections into each animal. As a control, we used radioactive microspheres (RAM) for six kidneys in three rabbits. There were no significant differences for RTBF values between NRACM and RAM, between the numbers of microspheres used (2 x 10(6) and 4 x 10(6)), or between the number of injections. These results showed that NRACM is a useful and safe laboratory method.

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

A standardized ischemic, H-shaped, double flap model in rats was developed for investigating the influence of different factors that could potentially increase flap survival. The blood flow was measured in the flaps as well as in normal healing incisional wounds on day -1 (intact skin) and on days 1, 4, 8, and 16 by the xenon-133 (133Xe) clearance technique. The flow in normal healing incisional wounds remained the same as the flow in intact skin. The flow in the flaps, however, initially decreased to ischemic levels, but afterwards gradually increased to that of normal healing incisional wounds and intact skin. Further, the cutaneous blood flow in both the cranially and the caudally based ischemic dorsal flap was independent of the width of the flap.

Protection of pig epidermis against radiation-induced damage by the infusion of BW12C

BW12C, which was developed as an agent for the treatment of sickle cell anaemia, increases the binding of oxygen to haemoglobin and hence reduces the availability of oxygen to tissues. Due to these changes in oxygen availability BW12C could act as a protector against radiation-induced injury to normal tissues. In this study the potential value of BW12C, as a radioprotector, was studied in the irradiated epidermis of the pig. The infusion of BW12C caused an instant left shift of the oxygen dissociation curve, an effect that lasted for approximately 1.5 h. This left shift in the oxygen dissociation curves increased with increasing dose of the drug. There appeared to be no long-term systemic effects produced by doses of 20-100 mg/kg of BW12C. In the first 90 min after the infusion of BW12C skin fields were irradiated with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint for assessing the severity of the radiation response. With animals breathing approximately 70% oxygen in the anaesthetic gas mixture, the ED50 values for moist desquamation were 30-31 Gy after a dose of 30 and 50 mg/kg, and 37-38 Gy for 75 and 100 mg/kg doses of BW12C. These ED50 values were significantly higher than the value of 27.3 Gy for radiation alone. This indicated dose modification factors (DMF) with mean values of approximately 1.13 and approximately 1.40 for irradiation following the infusion of low (30-50 mg/kg) and high (75-100 mg/kg) doses of the drug, respectively. With the animals breathing air (approximately 21% of oxygen) in the 2% halothane anaesthesia gas mixture, irradiation in the presence of 30 and 50 mg/kg of BW12C resulted in ED50 values of approximately 39 Gy for moist desquamation, which was significantly higher than the value of 31.2 Gy for radiation alone. Surprisingly, a higher dose of 75 mg/kg of BW12C resulted in a lower ED50 value for moist desquamation of 34.38 Gy. Irradiation in the presence of a dose of 100 mg/kg of BW12C produced an ED50 value which was not significantly different from that for radiation alone. In the situation where animals were breathing air (approximately 21% oxygen) during irradiation a DMF of 1.14 was obtained for irradiation alone, when the results were compared with those for irradiation alone with approximately 70% oxygen in the anaesthetic gas mixture.(ABSTRACT TRUNCATED AT 400 WORDS)

The veno-arteriolar reflex in free skin flaps

The veno-arteriolar reflex was measured in 10 subjects in whom an area of denervated skin was present in the lower limb following free flap transfer of skin and subcutaneous tissue 3 weeks to 2 years previously. The vasoconstrictor response to dependency was measured in the skin of the flap, in adjacent innervated skin and after chemical dilatation of cutaneous vessels in the skin of the flap. This veno-arteriolar reflex resulting in a reduction of blood flow of 30-40% was present and equal in both normal and denervated skin. The response was abolished by chemical vasodilatation. The results indicate that sympathetic innervation is not essential for the veno-arteriolar reflex, and suggest that myogenic mechanisms may be more important than previously believed.

Observations on dermal blood flow as reflected by technetium-99m pertechnetate clearance

Skin blood flow as reflected by the clearance rate of intradermal injections of Technetium-99m (99mTc) was studied in the skin of human volunteers and in a variety of clinical situations. In volunteers comparisons between the effect on clearance following intradermal injections of either lignocaine or lignocaine/adrenaline showed that the latter resulted in a dramatic reduction in the clearance rate of the technetium isotope and that such clearance curves exhibited no fast component. Clinical studies in grossly ischaemic skin revealed a similar absence of the fast component of isotope clearance and this was also the case for healed split thickness skin grafts. The dermal isotope clearance was also used in pedicle skin flaps both before and after clamping the axial pedicle in order to derive clearance ratios which would reflect the degree of neovascularisation to the flap. These preliminary observations suggest that the technique is safe, and easy to use in many clinical circumstances. We consider that it offers a valuable method by which changes in dermal blood flow may be quantified, when simultaneous control areas of isotope clearance are also studied. Suggestions are made for further avenues of study.

Quantitative analysis of skin flap blood flow in the rat using laser Doppler velocimetry

Two experiments carried out on rat skin flaps are described, where microvascular flow has been measured noninvasively by a laser Doppler velocimeter. Using this technique it is possible to define the limits of an axial pattern flap in terms of microvascular flow; this was found to increase when the flap is elevated. 'Random-pattern' perfusion is defined by a fall in flow. This recovers sequentially along the flap, and at a constant rate at all sites. A differential in microvascular perfusion is thus maintained along a random-pattern flap for at least the first postoperative week. In a second experiment it is shown that there appears to be a linear relationship between the reduction in skin blood flow in a random-pattern flap and the distance from the base at which the measurements are made. It is suggested that these data support the view that the blood flow in a skin flap recovers primarily from its base rather than via peripheral neovascularization, and that this is due to vascular collaterals opening within the flap rather than to a relaxation of sympathetic tone.

Laser Doppler surveillance of the circulation of free flaps and replanted digits

In a series of 40 clinical free flaps and replantations the laser doppler technique has been used successfully for postoperative surveillance of circulation. A uniform flow pattern was obtained from all uncomplicated cases contrasting to the flow pattern seen in cases with thrombotic complication. The laser doppler continuously records flow of the microcirculation and is able to monitor blood flow in all types of free tissue transfer presently used as well as replantations. The laser doppler has effectively diagnosed two arterial thromboses with a characteristic flow pattern. It can distinguish venous from arterial occlusion. It can record flow in skin flaps which are difficult to judge clinically and in buried flaps, where no clinical observations are possible. The laser doppler should be used in conjunction with routine clinical observations.