investigations in diabetes mellitus · activeisotopessuchas'33XeandNal31Icanbeused to...

Postgrad Med J (1993) 69, 419-428 © The Fellowship of Postgraduate Medicine, 1993

Review Article

Microvascular investigations in diabetes mellitus

Sandra J. Chittenden and Shukri K. Shami

Department of Surgery, University College and Middlesex School of Medicine, London, UK

Summary: This paper reviews the current literature concerning the different investigative modalitiesavailable to assess the microcirculation in diabetic microangiopathy. The advantages and disadvantages ofthe different invasive and noninvasive methods available are presented objectively. We have concentratedon the tests that provide a quantitative assessment of the microcirculation, including laser Dopplerfluxmetry, capillary microscopy, plethysmography, transcutaneous oximetry and radioactive isotopeclearance. Some of the invasive methods described are now being replaced by noninvasive equivalents,providing similar information with less discomfort and risk to the patient.

Introduction

The complications resulting from diabetic angio-pathy can be severe and debilitating. An enormousamount of research has been undertaken to try toclarify the mechanisms by which microangiopathyoccurs but has so far yielded no clear answer. Thedevelopment of microangiopathy is probablymulti-factorial in origin and includes genetic sus-ceptibility. Factors that are thought to contributetowards the formation ofmicroangiopathy includethose shown in Table I(a).'

Unfortunately, by the time microvascular chan-ges become clinically evident, there is often littlethat can be done in the way of treatment. It wouldbe advantageous to identify those patients at risk ofdeveloping severe retinal and glomerular impair-ment and neuropathic or atherosclerotic lesions.Functional microvascular changes may occur earlyon in the development of clinical angiopathy andinvestigation of the microcirculation might there-fore provide a means of detecting angiopathybefore it becomes clinically evident. Microvascularmeasurement techniques are also used clinically inthe assessment of sympathetic neuropathy2 andinvestigation of the peripheral microcirculationmay provide a way of detecting neuropathy in itsearliest stages.3'4

In research, microcirculatory investigationsmight be used to provide an objective test ofdifferent modes of treatment. In addition, any

information about the nature of the microcir-culatory fault in diabetic angiopathy may help inunderstanding its aetiology and in developing newtreatment strategies. Many of the invasive techni-ques for microvascular measurement have beensuperseded by noninvasive techniques, which isclearly advantageous for the investigation of micro-angiopathy in the diabetic patient. This reviewplaces more emphasis on the noninvasive techni-ques available.

Importance ofmacrovascular assessment

Care must be used in the interpretation of micro-vascular assessments if macro- and microvasculardisease coexist, and this is often the case, diabeticpatients being more prone to cardiovascular andperipheral arterial disease than non-diabetics.5'6The reasons for diabetics being more prone tomacroangiopathy are not certain but probablyinclude the factors shown in Table I(b).5'7-'5 Oc-clusive macrovascular disease may impede theability ofthe microcirculation to respond to a givenstimulus. It is therefore important to evaluate theextent of one source of circulatory dysfunction inorder to study the other.

Microvascular investigations

An investigation of vessel morphology may beinformative about angiopathy in its later stages andcan help to assess its progression. However, inorder to identify microcirculatory problems earlieron in their development, a functional assessment ofthe microcirculation may be more useful. Thisusually consists of measuring blood flow, either in

Correspondence: S.K. Shami, F.R.C.S., M.S., SurgicalStudies, Jules Thorn Building, Middlesex Hospital,Mortimer Street, London W1N 8AA, UK.Accepted: 30 November 1992

copyright. on M

ay 27, 2021 by guest. Protected by

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.69.812.419 on 1 June 1993. D

ownloaded from

http://pmj.bmj.com/

420 S.J. CHITTENDEN & S.K. SHAMI

Table I Factors of importance in the pathogenesis of diabetic micro- and macroangiopathy

(a) MicroangiopathyHyperglycaemia Results in nonenzymic glycosylation of proteins in the vessel wallsInsulin-immune complexes Stimulate monocytes and macrophages to produce procoagulant activity'Platelet activation Initiates thrombosis, release of angiogenic factors such as PDGF and the

transforming growth factors (TGF)-alpha and TGF-beta, and the release ofvasoconstrictor substances such as thromboxane A2

Endothelial activation Results in increased permeability and release of vasoactive substancesMacrophage and monocyte Produces free radicals (superoxides, hydroxyl radicals and peroxides) andactivation cytokines and causes vascular damage

(b) MacroangiopathyHyperglycaemia A risk factor in atherogenesis5 which increases adherence of monocytes and

macrophages to the vessel walls7'8 and may result in local accumulation ofvasoactive substances, increased proliferation of endothelium due to therelease of growth factors, and damage to the vessel wall by free radicals

Free radicals Increased free radical activity is seen in diabetes9"0 and may be involved inmicrovascular damage"'12

Lipoproteins Concentrations of low density lipoproteins and very low density lipo-proteins are high in patients with poorly controlled diabetes1314 and thismay be important in atherogenesis. High density lipoproteins are said tohave a protective role in atherogenesis and are lower in some diabetics'5

Hypertension Not considered a 'very important factor in vascular disease in diabetes' bymost authors

Other factors Including: hyperinsulinaemia, rheological factors, growth factors, reducedphysical activity, obesity and genetic factors

PDGF = platelet-derived growth factor.

the steady state or in response to some provoca-tion. The resting skin blood flow in diabeticpatients is often shown to be normal and yet themaximal flows are impaired.16"7 Since there hasbeen some difficulty in finding abnormal data atrest (possibly because of some redundancy in thecontrol of local flow'8) many studies use some kindofprovocation in order to expose a latent problem,for example, looking at blood flow either duringexercise, while raising body temperature, afteradministering vasoactive substances'9 or followingtissue ischaemia. The actual pattern of the bloodflow response to a challenge such as ischaemia maybe important.2 In diabetes mellitus, return ofblood flow after ischaemia is impaired in the skin ofthe toes21 and in the nailfold22 (although it occursmore rapidly in leg muscle'6). The cold recoverytime of skin blood flow is also longer.23Another way to study the function of the micro-

circulation is to evaluate reflexes such as thereduction of blood flow normally seen on standing(the veno-arteriolar reflex). This is impaired inpatients with diabetic neuropathy.24 Similarly, inthe retina, the vasoconstriction normally caused byhigh oxygen tension is blocked by hyperglycae-mia.'6'25 Care must be taken in interpreting thechanges in blood flow induced by such stimuli sincethere are various controlling influences that may beat work. These include sympathetic nerve activity,local autoregulatory mechanisms, venous reflexesand the status of arterio-venous shunts. Thermal

entrainment studies suggest that the central andlocal regulatory mechanisms provide coarse andfine microvascular control respectively.26 It istherefore important to investigate the differentsystems separately, using both contralateral andlocal stimuli. It is also desirable to study flow inboth the arterio-venous shunt vessels and thenutritional capillaries in the skin. Unfortunately,most studies to date are unable to distinguishbetween flow in these different vessels.

It may be meaningful to study the effects ofmicrocirculatory changes on the chemical milieu ofthe tissues, including oxygen tension, to determinewhether observed microvascular alterations haveany functional significance. Nuclear magneticresonance (NMR) spectroscopy may be employedto study this by examining the redox status withinthe tissues. One approach, which has not beenexploited as yet, might be to study the fluorescenceof the mitochondria as their metabolic statechanges.

Investigative techniquesBlood tests and other nonspecific tests

It would be useful if a simple clinical examinationor a laboratory test carried out on the blood orurine samples routinely taken from diabetic pa-tients could show or predict the development of

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/

MICROVASCULAR INVESTIGATIONS IN DIABETES 421

angiopathy. It is known that hyperglycaemia has atleast a permissive role in the aetiology of diabeticlesions, such as retinopathy and nephropathy.27Monitoring the levels of glucose or glycosylatedhaemoglobin in the blood and attempting optimalglycaemic control may therefore help in preventingthe development of microvascular complications.However, the relationship between these factors isnot strict and metabolic control is of little use oncemicroangiopathies have developed. One of thestandard tests for diabetic microangiopathy ismicroalbuminuria, resulting from glomerular dys-function. Early elevation of transcapillary leakageof albumin in the kidney (incipient nephropathy) issaid to be the first sign ofmicrovascular disease.28 Ifperformed regularly in all diabetic patients, this testmight facilitate the detection of angiopathy in itsearliest clinical stages, but there are obvious finan-cial and practical limitations. Another marker forangiopathy is a slight increase in blood pressure,although this is not very specific. An increased levelof plasma von Willebrand factor has been pro-posed as an indicator of microangiopathy since itselevation is associated with retinal hyperperme-ability.29 Angiotensin converting enzyme (whichcleaves angiotensin I to angiotensin II and inac-tivates bradykinin) is also high in some diabeticpatients and these have a higher incidence ofretinopathy. Angiotensin converting enzyme wastherefore thought to indicate widespread endo-thelial damage in microvascular disease.30 How-ever, it is increased in only a small percentage ofpatients with microangiopathy and is a less reliableindicator than von Willebrand factor. Increasedplasma levels ofinactive renin may also be a markerfor microvascular complications. Although indiabetic patients without microvascular complica-tions, plasma inactive renin concentrations liewithin the normal age-adjusted range, in thosepatients with retinopathy or albuminuria it isnearly always above this range.31 Similarly, limitedjoint motility in childhood diabetes mellitus indi-cates an increased risk for microvascular disease.32The problem with many of these tests is that theyindicate the presence of some process whichaccompanies angiopathy, rather than measuring itdirectly. They may therefore be useful as epidemio-logical pointers but are of little help in predictingand following angiopathy in an individual patient.Invasive techniques

Many of the microcirculatory changes in diabeticmicroangiopathy were originally discovered usinginvasive techniques. Although in some cases thesetechniques have since been replaced by noninvasivemethods, in others there is no substitute for theinvasive approach. Instead, the methods have beenmade as atraumatic as possible. For example, in

order to study capillary permeability and blood-tissue exchange, it is usually necessary to introducelabelled tracer substances invasively. However,their movement can now be monitored non-invasively, so reducing the trauma presented by theinvestigation.

Histology Histological tissue measurement tech-niques show that blood vessel walls are thicker indiabeties mellitus and vascular lumina are nar-rower, especially in those patients with vascularcomplications.33 Capillary basement membranethickening has been said to be the hallmark ofmicrovascular disease.34 However, it occurs inparallel with microangiopathy, rather than being acause, and tissue biopsy for investigation of base-ment membrane thickness is a poor substitute for afunctional assessment of the microcirculation.35

Local clearance (bloodflow) Clearance of radio-active isotopes such as '33Xe and Nal31I can be usedto measure perfusion. By injecting '33Xe into mus-cle36'37 or skin38 its rate of disappearance can beused to measure local blood flow. 133Xe clearance isthought to reflect blood flow since it is freelydiffusible and fat soluble and crosses all vascularbarriers. In contrast, the clearance ofNa'31I may belimited by capillary permeability rather than bloodflow. This means that in diabetes, where capillarythickening is often seen, rates of blood flow may beunderestimated by Nal31I clearance rates alone.39Using combined xenon and sodium clearancemeasurements it is possible to study vessel-tissueexchange as well as blood flow.37

Skin perfusion pressures In this technique, anintradermal injection of a radioactive tracer mixedwith histamine (to promote vasodilatation) is givenand the washout measured with a scintillationcounter." A blood pressure cuff is applied over theinjection site and the pressure in it increased untilwashout stops. This cuff pressure is taken as theskin perfusion pressure (SPP). A number of differ-ent radioactive tracers, including '31I-antipyrine and99mpertechnate, have been used. This technique hasits disadvantages, as it is time consuming, espe-cially if the SPP is to be determined at more thanone site, and painful enough to require analgesia.An alternative new approach using either aphotoplethysmography transducer41 or a laserDoppler probe (see laser Doppler fluxmetry below)underneath an inflatable cuff may be more useful.

Capillary filtration and permeability Increasedcapillary diffusion capacity (CDC) has been dem-onstrated by various investigators in differenttissues (such as skeletal muscle,37'42'43 retina44 andnerves45) for small ions,37'42 dopamine,46 fluor-

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


escein,29'47 albumin,48 IgG49 and 131I.50 Microvas-cular permeability is related to the metabolic stateand may be reduced by metabolic regulation.5 Thepermeability of the vascular diffusion barriers, i.e.the capillary wall and pericapillary collagen sheath,can be measured using the 'relatively atraumatictechnique' of intravital fluorescence videomicro-scopy,47 especially in the eye44'52 and nailfold.22Sodium fluorescein passes the capillary wall andpericapillary space faster in diabetic patients. How-ever, the results of such studies should be inter-preted with caution, since there may be effects dueto, for example, the lymphatic return of the tracersor to the labelled substances being handleddifferently from unlabelled ones.53

Measurement of capillary pressure using micro-pipettes Capillary pressure can be measureddirectly using a microinjection technique.54'55 Usingthis method the pressure in the arteriolar end, theloop and the venular end of the capillary can bemeasured, and an assessment of the pressuresresponsible for fluid filtration and reabsorptionevaluated. Nailfold capillary pressure have beenfound to be elevated in young insulin-dependentdiabetics in the early stages of disease.5 Theregulation of pressure in relation to skin tempera-ture is also disturbed and the pressure duringpostocclusive reactive hyperaemia is less than innormal subjects.57Noninvasive techniquesIt is preferable that any routine investigations benoninvasive. Some of the tests described abovehave been abandoned since the information neededcan be obtained using the noninvasive tests des-cribed below. Such tests are less traumatic to thepatient and can be repeated as necessary to assessthe development and progression of angiopathy.Vessel morphology Abnormalities in vessel mor-phology can be investigated using in vivo micro-scopy as well as by histological methods. Dilatednailfold capillaries have been found, and welldefined in diabetes mellitus.22'58 59 However, there isa difference in capillary morphology even betweentoes on the same foot60 and so care must be taken inmaking measurements. The first retinal lesions indiabetic retinopathy can be seen noninvasively byfundoscopy or even earlier using fluoresceinangiofluorography.6'Skin temperature and thermal clearance The tem-perature of the skin tends to increase as the bloodflow increases. It can be measured most simplyusing thermocouples, although many studies usethermography which is useful for showing grosschanges, such as the cessation and recommencing

offlow. However, skin temperature has a nonlinearrelationship with blood flow, especially at higherlevels (above 28°C) and responds slowly to flowchanges, lagging behind them.62 Skin temperaturemay be useful for demonstrating large changes inthe perfusion of skin after drug therapy63 orsurgery. The maximum increase in finger skintemperature following ischaemia is decreased indiabetes mellitus33 and is still less in those patientswith vascular complications.Thermal clearance probes have been used to

measure blood flow noninvasively in the skin.64 Theprobes consist typically of a heated central copperdisc with an unheated copper annulus. The tem-perature difference between these is measured usingthermocouples and decreases as the blood flowbeneath the probe increases.65 Although, in muscle,the measurement depends greatly on the proximityof the probe to a blood vessel,66 in the skin, thermalclearance probes measure total skin blood flow(including flow through arterio-venous anastomosesin the microcirculation) and not nutritive flowonly.67 The technique can give important inform-ation about flow distribution, especially if used inconjunction with a measure of total flow, such aslaser Doppler flowmetry.66 An alternative methodis to measure the power consumption of a thermo-statically controlled heating element.68 The higherthe blood flow, the more rapidly heat will beremoved from the skin under the heating elementand the more power will have to be supplied tomaintain a fixed temperature. This approach isparticularly attractive when the heating elementused is that of a tcPo2 electrode or thermostaticallycontrolled laser Doppler probe holder. Oxygentensions and blood flow measurements have beenmade simultaneously in this way.68Venous occlusion plethysmography Various tech-niques of plethysmography have been used for themeasurement of limb blood flow. The method isable to give quantitative values after calibrationand is said to be accurate and reproducible.69 Itrelies on measuring volume changes, the rate ofincrease in limb volume following release of occ-lusion being used to measure blood flow rates. Theusual volumetric techniques are water displace-ment70 or a mercury-in-Silastic strain-gauge.71 Inthe hand and foot, values from venous occlusionplethysmography are assumed to reflect skin bloodflow since there is little muscle present. However, inthe arm and leg, the technique cannot distinguishbetween skin and muscle flow (unless used inconjunction with adrenaline ionophoresis66). Innormal subjects, under thermoneutral conditions,the muscle and skin contribute similarly to totallimb blood flow so that changes in total flow areassumed to reflect changes in skin and muscle flowequally, but this may not hold true for diabetic

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


patients.66 In addition, whilst a thermal stress in anon-diabetic patient results in changes in skinblood flow only, this may not be the case indiabetes. Additional problems with the techniqueare that alterations in tissue compliance occur witheach pulse and that a veno-arteriolar reflex may beinduced by cuff compression if it is high orprolonged.2

Strain gauge plethysmography has been used tostudy blood flow and capillary diffusion coefficientsin the forearm. Following release of occlusion, theinitial slope of the volume/time curve representsvenous filling, and is used to calculate blood flow.Vascular resistance and venous capacity can alsobe calculated. The shallower slope that followsafter a few minutes represents capillary filtration.This method is simple, quick and noninvasive.

Photoelectric plethysmography Using this techni-que, light is shone onto the skin where it is absorbedby both skin and blood.73 As the volume ofblood inthe skin increases, it absorbs more light and less isreceived by the detector. The method cannotdistinguish between nutritive and shunt flow and issensitive to movement and to the orientation andpacking of the red cells. If the light source used alsoproduces heat, it may cause vasodilatation whichwill interfere with the measurements. It cantherefore only be used for qualitative comparisons.The technique has now been largely superseded byother methods.

Laser Doppler fluxmetry

Many observations of blood flow, especially in theskin, have been made using laser Doppler flow-metry (LDF). This involves shining a laser lightinto the skin and measuring the back scatteredlight.74 Some of the incident light will strike movingred blood cells and be reflected with a shift in itsfrequency, caused by Doppler broadening, which isrelated to the speed of the cells. Studies in vitroshow that the mean Doppler frequency is propor-tional to the rate ofblood flow.74,75 In vivo studies inskin using '3Xe washout techniques confirm thislinearity75'76 and show that stable recordings can beachieved.76 A laser Doppler flowmeter provides asignal, used as a measure of blood flow, which isproportional to the number of red cells in thevolume penetrated by the laser beam and to theintegrated red cell velocity. The laser beam pene-trates through the skin and measures flow in avolume of several cubic millimeters. Although thebeam is supposed to reach a depth of 0.6 mm,74 itmaintains halfof its sensitivity at a depth of 1.2 mmand can still pick up some cell movement deeperthan this.66 This means that flow in small arteriolesand arterio-venous anastomoses may be includedso that LDF does not give a measure of flow in the

nutritional capillaries alone. The dependence ofLDF readings on depth of penetration means thatcare must be taken when comparing readings fromdiabetic patients in whom there may be epidermalthickening, with normal subjects. Synchronousmeasurement using LDF and microscopy in mus-cle77 and skin78 gives broadly comparable resultsbut not under all conditions.79 In the skin there aredifferences in the timing of spontaneous oscilla-tions, the time course of reactive hyperaemia andthe response to venous hypertension between thetwo measurement techniques. In addition, LDFcannot distinguish between capillary flow andshunt flow and it is therefore now regarded as ameasure of total blood flow in the skin.78 LDF maybe a particularly useful technique in diabetes wherethere is thought to be increased non-nutritive flowin the skin due to sympathetic denervation.66The laser Doppler flowmeter does not provide

absolute quantitative values relating to blood flowand calibration is difficult. The measurements showmarked variations over distances of less than1-2 cm66 and readings are generally regarded asnot repeatable, although one series of measure-ments demonstrated a coefficient of variation ofless than 12%.80 Although it may be valid toexamine the relative changes in flow within anindividual subject, comparisons of absolute bloodflow rates between groups are of doubtful validity,especially when there are changes which may affectthe laser Doppler signal (such as the glycosylationof connective tissues or thickening of capillarybasement membranes seen in diabetic angiopathy).

In spite of its limitations, LDF is better validatedas a measure of superficial microvascular volumeflow rate than its predecessor photoelectric plethys-mography.81 Using LDF it has been demonstratedthat basal blood flow in the skin is not altered indiabetes mellitus but that maximal flows areimpaired.8 Blood flow has also been measured inthe retinal arterioles in diabetes mellitus usingLDF.83

Capillary microscopy Microscopy facilitates thedirect and noninvasive study of the capillaries inthe upper layers of the skin84 and in this waymorphological abnormalities can be observed. Inaddition to such static investigations, blood flow inthe capillaries can be measured. Some work hasinvolved tracers such as fluorescein to measureretinal blood flow.61 In other studies, the capillaryblood velocity itself is measured84'85 and along withcapillary morphometry and estimation of therelative haematocrit, this allows volume flow pat-terns to be studied.86'87 Because the capillaries areunder direct observation, microscopy is the onlytechnique in which it is certain that nutritive bloodflow alone is being measured. Simultaneous LDFand capillary blood velocity measurements have

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


been used to demonstrate discrepancies betweentotal and nutritional flow in skin.77'78

Early studies used time-consuming frame-by-frame analysis of capillary images recorded onvideo tape.88 This involves locating the position ofacell group or plasma gap, advancing the tape byseveral frames and measuring the new position ofthe cells and gaps. The velocity can be calculatedfrom the distance moved in a set time (which is thenumber of frames multiplied by 1/25 or 1/30seconds). In the simpler 'flying spot' technique,89the speed of a moving spot superimposed on thevideo image is adjusted until it moves at the samerate as the red cells. The analysis can be carried outin real time but is subject to user-error and cannotdetect rapid changes in velocity.More sophisticated techniques have also been

developed, based on early photodetector meth-ods.90 They rely on the principles of cross-cor-relation, in either the space84 or the time85 domains,to match up the patterns created as dark red cellsand light plasma gaps pass the photodetectors (or awindow in the video image).

Subject movement presents a significant problemwhen these techniques are applied in humans. Ifthearea being studied moves even slightly underneaththe microscope objective, then the capillaries willmove within the video image. Attempts have beenmade to immobilize the area under study usingspecial casts or brackets9l but these do not alwayscompletely eliminate movement and may interferewith blood flow. Newer systems compensate for themovement by either tracking a capillary as it movesaround in the image,86'87 or by performing atwo-dimensional cross-correlation on a small areaof the image ('CapiFlow system for the evaluationof video recorded dynamic capillary blood flowparameters', CapiFlow AB, Sweden). Using suchtracking methods, velocimetry can be carried out inreal time on capillary microscopy images in whichthere is subject movement. The technique is stilltime consuming, especially when several capillariesare studied, but is much less so than earliermethods.

Unfortunately the technique of velocimetryusing noninvasive capillary microscopy is onlyapplicable to certain sites such as the nailfold andonly a small sample ofcapillaries can be studied at atime. The velocity of blood flow in the differentcapillaries may differ substantially. Since there aredifferences in capillary morphology even betweenthe toes of the same foot,60 it is important tostandardize the site of measurement. Capillarymicroscopy does, however, permit characterizationof the size, shape and number of vessels present sothat the influence of these parameters on bloodflow can be studied.

In spite of its limitations, microscopy is stillregarded as the 'gold standard' for measuring

capillary blood flow against which other techniquesmust be judged.78 Capillary microscopy has beenused to demonstrate dilated capillaries and delayedreturn of local blood flow after ischaemia indiabetes mellitus.22

Noninvasive measurement of capillary filtrationThe invasive measurement of capillary filtrationcoefficients (CFCs) has been described above.Capillary filtration can also be measured non-invasively by venous occlusion plethysmography(described above). The slower part of the volume/time curve represents extravasation of plasma intothe tissues as a result of elevated venous pressure.The CFC is normal or depressed early on indiabetes92 but increases with duration and becomeselevated in long-standing diabetes.93 Although partof this increase may be an artefact,53 due toimpairment of the veno-arteriolar reflex in diabeticpatients,94 such effects are not entirely responsiblefor increased filtration94 and so there is a realincrease in the CFC in long-duration diabetes.

Noninvasive measurement of xenon clearance Ashas been discussed, clearance of the radioactiveisotope '33Xe has been used to measure blood flowin the skin.38 In order to avoid the initial hyper-aemia due to injection trauma, 33Xe can also beintroduced epicutaneously via a small chamberattached to the skin.95 Since its molecular weightand solubility are similar to those of oxygen, 133Xeuptake has been used as an indicator of vascularpermeability in assessing the oxygen diffusionbarrier in chronic venous disease.95

Transcutaneous oxygen tension Transcutaneousoxygen pressures have been used to study the endresult of perfusion and diffusion effects in diabetesmellitus by monitoring tissue oxygenation. Somestudies show that the transcutaneous pressure ofoxygen (tcPo2) is slightly lower in patients withdiabetes mellitus than in normal subjects.96 How-ever, it is not clear how well skin oxygen pressuresreflect the normal levels of oxygen in the tissues.The technique of measuring tcPo2 was originally

developed for monitoring arterial oxygenation inneonates. In order to make these measurements, itis necessary to 'arterialize' the skin by heating it to43 or 44°C.97 This produces a local hyperaemia, sothat excess oxygen diffuses across the skin to amodified Clarke electrode in the tcPo2 probe whereit is chemically reduced and measured. TcPo2measured using a heated probe thereafter does notshow actual tissue oxygenation under normal phys-iological conditions. When arterial Po2 is adequate,tcPo2 changes with blood flow and when blood flowis adequate, tcPo2 reflects the arterial oxygensaturation.

Heating the skin to 44°C produces a 20-fold

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


increase in blood flow in diabetic patients com-pared with a 40-fold increase in normal subjects asmeasured by LDF.24 Care must therefore be takenin choosing the electrode temperatures and ininterpreting the results since any differences seenmay reflect an inability to increase the nutritionalblood flow at 44'C. When skin oxygen tension invenous disease is measured at 37°C, there is nodifference between patients and controls at rest,98whereas there is at 44°C. The poor oxygenation ofthe tissues sometimes found using tcPo2 measure-ments in diabetes mellitus63'96 may therefore be aresult of the method of measurement rather than atrue pathophysiological feature. Furthermore, al-though the capacity for the microvessels to vaso-dilate and increase their flow to supply oxygen tothe tcPo2 probe may be reduced in diabetes, there isno evidence that this has any functionalsignificance and patients with diabetes mellitus areprobably still able to supply their tissues withsufficient oxygen.Although few studies actually show a

significantly lower tcPo2 in diabetics at rest, pos-sibly because ofredundancy in control oflocal flowand metabolic accommodation to modesthypoxia,18 more pronounced differences can beevinced using an oxygen inhalation test.99 In Breueret al.'s study,96 although the basal tcPo2 is onlyslightly lower in diabetics, there are moresignificant differences when breathing 5 and 10litres of oxygen per minute. However, what isactually being measured is the system's maximalcapacity to supply oxygen under conditions ofhyperaemia and hyperoxia. Nevertheless, the rateof rise of oxygen concentration is slower indiabetics, whilst the time to the maximum level is

the same9 and such functional studies are able toshow differences between diabetic patients andcontrols before there are any clinical or mor-phological signs of microangiopathy.

In measuring tcPo2, a control electrode is oftenused, placed in the subclavicular area. The tcPo2 inthe area of interest is then related to this, the ratiobeing used to give a regional perfusion index."°Such indices may provide better discriminationthan single tcPo2 values.

tcPo2 readings are dependent on arterial andvenous blood pressures,'10 arterio-venous pressuredifferences'02 and changes in venous P02, and arelinearly related to the blood flow under the elec-trode.68'103 Epidermal thickness also has aninfluence, tcPo2 falling as the thickness increases.04In addition, tcPo2 measurements depend on capil-lary density'05 and the number of perfusedsuperficial capillaries06 and may also be affected byangiopathy in these capillaries. Other factors havealso been shown to affect tcP02, includinginflammation, oedema and the skin's oxygen con-sumption. Care must be therefore used whenmaking comparisons of absolute tcPo2 levels,especialy when studying diabetic subjects, who areknown to differ in some of these variables.

tcPo2 may be better for measuring inducedresponses such as postocclusive hyperaemia'07 thanbasal blood flow. However, great care must betaken when using the heated tcPo2 to monitormicrovascular responses in this way, since it hasbeen shown that heating the skin to 43 or 44°Cabolishes both periodic changes in blood flow andthe normal blood flow regulation by local reflexesor vasodilatory substances.68,'08

References

1. Uchman, B., Bang, N.U. & Rathbun, M.J. Effect of insulinimmune complexes on human blood monocyte and endo-thelial cell procoagulant activity. J Lab Clin Med 1988, 112:652-659.

2. Low, P.A., Neumann, C., Dyck, P.J. et al. Evaluation ofskinvasometer reflexes by using laser Doppler velocimetry.Mayo Clin Proc 1983, 58: 583-592.

3. Archer, A.G., Roberts, V.C. & Watkins, P.J. Blood flowpatterns in painful diabetic neuropathy. Diabetologia 1984,27: 563-567.

4. Shore, A.C., Price, K.J., Tripp, J.H. et al. Functionalassessment of the microcirculation in children with diabetesmellitus. Conference Proceedings. Joint Meeting of theItalian andBritish Microcirculation Societies, Exeter Univer-sity, 1989.

5. Brand, F.N., Abbott, R.D. & Kannel, W.D. Diabetes,intermittent claudication, and risk of cardiovascular events.The Framingham study. Diabetes 1989, 38: 504-509.

6. Jonason, T. & Ringqvist, I. Diabetes mellitus and intermit-tent claudication. Relation between peripheral vascularcomplications and location of the occlusive atherosclerosisin the legs. Acta Med Scand 1985, 218: 217-221.

7. Setiadi, H., Wautier, J., Courillon-Mallet, A. et al. Increasedadhesion to fibronectin and MO-1 expression by diabeticmonocytes. J Immunol 1987, 138: 3230-3234.

8. Brownlee, M., Vlassara, H. & Cerami, A. The pathogeneticrole of non-enzymatic glycosylation in diabetic complica-tions. In Crabbe, M.J.C. (ed.) Diabetic Complications:Scientific and Clinical Aspects. Churchill Livingstone, Edin-burgh, 1987, pp. 94-139.

9. Jennings, P.E., Jones, A.F., Florkowski, C.M. et al. In-creased diene conjugates in diabetic subjects with microan-giopathy. Diabetic Med 1987, 4: 452-456.

10. Collier, A., Wilson, R., Bradley, H. et al. Free radicalactivity in Type 2 diabetes. Diabetic Med 1990, 7: 27-30.

11. McCord, J.M. Oxygen-derived free radicals in post-ischaemic tissue injury. N Engl J Med 1985, 312: 159-163.

12. Wolff, S.P. The potential role of oxidative stress in diabetesand its complications: novel implications for theory andtherapy. In: Crabbe, M.J.C. (ed.) Diabetic Complications:Scientific and Clinical Aspects. Churchill Livingstone, Edin-brugh, 1987, pp. 167-220.

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


13. Lopes-Virella, M.F., Wohltmann, H.J., Mayfield, R.K. etal. Effect of metabolic control on lipid, lipoprotein andapolipoprotein levels in 55 insulin-dependent diabeticpatients - a longitudinal study. Diabetes 1983, 32: 20-25.

14. Sosenko, J.M., Beshow, J.L., Meittinen, O.S. et al. Hyper-glycaemia and plasma lipid levels: a prospective study ofyoung insulin-dependent diabetic patients. N Engl J Med1980, 302: 650-654.

15. Feher, M.D., Stevens, J., Lant, A.F. et al. Importance ofroutine measurement of HDL with total cholesterol indiabetic patients. J R Soc Med 1991, 85: 8-11.

16. Christensen, N.J. Muscle blood flow, measured by xenon133and vascular calciferations in diabetics. Acta Med Scand1968, 183: 449-454.

17. Sigroth, K. Reflex vasodilatation of the fingers in the studyof peripheral vascular disorders: with special reference todiabetes mellitus. Acta Med Scand Suppl. 1957, 325:1-116.

18. McMillan, D.E. The microcirculation: changes in diabetesmellitus. Mayo Clin Proc 1988, 63: 517- 520.

19. Weindorf, N,. Shultz-Ehrenburg, U. & Altmeyer, P. Diag-nostic assessment of diabetic microangiopathy by TcPO2stimulation tests. Adv Exp Med Biol 1987, 220: 83-86.

20. Jorgensen, R.G., Russo, L., Mattiol, L. et al. Early detectionofvascular dysfunction in type 1 diabetes. Diabetes 1988, 37:292-296.

21. Christensen, N.J. Spontaneous variations in resting bloodflow, post ischaemic peak flow and vibratory perception inthe feet of diabetics. Diabetologia 1969, 5: 171-178.

22. Fagrell, B., Hermansson, I.-L., Karlander, S.-G. et al. Vitalcapillary microscopy for assessment of skin viability andmicroangiopathy in patients wtih diabetes mellitus. ActaMed Scand Suppl 1984, 687: 25-28.

23. Hatanaka, H., Matsumoto, S., Kitamura, Y. et al. Skinblood flow in diabetic patients during cold loading. Kobe JMed Sci 1989, 35: 131-136.

24. Rayman, G., Williams, S.A., Spencer, P.D. et al. Impairedmicrovascular hyperaemic response to minor skin trauma intype I diabetes. Br Med J 1986, 292: 1295-1298.

25. Atherton, A., Hill, D.W., Keen, H. et al. The effect of acutehyperglycaemia on the retinal circulation of the normal cat.Diabetologia 1980, 18: 233-237.

26. Lafferty, K., De Trafford, J.C., Roberts, V.C. et al. On thenature of Raynaud's phenomenon: the role of histamine.Lancet 1983, 2: 313-315.

27. Tchobroutsky, G. Why do some diabetics develop severemicrovascular complications? J Diabetic Complications1989, 3: 1-5.

28. Viberti, G.C., Hill, R.D., Jarrett, R.J. et al. Micro-albuminuria as a predictor of clinical nephropathy ininsulin-dependent diabetes mellitus. Lancet 1982, i:1430-1432.

29. Porta, M., Townsend, C., Clover, G.M. et al. Evidence forfunctional endothelial cell damage in early diabeticretinopathy. Diabetologia 1981, 20: 597-601.

30. Lieberman, J. & Sastre, A. Serum angiotensin-convertingenzyme: elevations in diabetes mellitus. Ann Intern Med1980, 93: 825-826.

31. Luetscher, J.A., Kramer, F.B., Wilson, D.M. et al. Increasedplasma inactive renin in diabetes mellitus indicates increasedrisk for microvascular disease. N Engl J Med 1981, 305:191-194.

32. Rosenbloom, A.L., Silverstein, H., Lezotte, D.C. et al.Limited joint motility in childhood diabetes mellitusindicates increased risk for microvascular disease. N Engl JMed 1981, 305: 191-194.

33. Ajjam, Z.S., Barton, S., Corbett, M. et al. Quantitativeevaluation of the dermal vasculature of diabetics. Q J Med1985, 54: 229-239.

34. Siperstein, M.D. Diabetic microangiopathy. Genetics,environment, and treatment. Am J Med 1988, 85(Suppl 5A): 115-130.

35. Doran, T.L. & Tattersall, R.B. Blind alleys in diabetesresearch: muscle capillary basement thickening: marker ofmicrovascular complications or false prophet? Diabetic Med1986, 3: 413-418.

36. Lassen, N.A., Lindbjerg, J. & Munck, O. Measurement ofblood-flow through skeletal muscle by intramuscular injec-tion of xenon-133. Lancet 1964, 1: 686-689.

37. Trap-Jensen, J., Alpert, J.S., del Rio, G. et al. Capillarydiffusion capacity for sodium in skeletal muscle in long-termjuvenile diabetes mellitus. Acta Med Scand (Suppl) 1967,476: 135-146.

38. Moore, W.S. Determination of amputation level: measure-ment of skin blood flow with Xenon Xe 133. Arch Surg 1973,107: 798-802.

39. Roddie, I.C. Circulation to skin and adipose tissue. In:Shepherd, J.T. & Abboud, F.M. (eds) Handbook of Physi-ology. The cardiovascular system: peripheral circulation andorgan blood flow. Section 2, Vol III, Part 1, Chapter 10.American Physiological Society, Bethesda, MD, 1983,pp. 285-317.

40. Holstein, P., Lund, P., Larsen, B. et al. Skin perfusionpressure measured as the external pressure required to stopisotope washout: methodological considerations and thenormal values on the legs. Scand J Clin Lab Invest 1977, 37:649-659.

41. van den Broek, T.A.A., Dwars, B.J., Rauwerda, J.A. et al.Photoplethysmographic selection of amputation level inperipheral vascular disease. J Vasc Surg 1982, 8: 10-13.

42. Leinonen, H., Maitkainen, E. & Juntunen, J. Permeabilityand morphology of skeletal muscle capillaries in type 1(insulin-dependent) diabetes mellitus. Diabetologia 1982,22:158-162.

43. Alpert, J.S., Coffman, J.D., Balodimos, M.C. et al. Capillarypermeability and blood flow in skeletal muscle of patientswith diabetes mellitus and genetic prediabetes. NEnglJMed1972, 286: 454-460.

44. Krogsaa, B., Lund-Andersen, H., Mehlsen, J. et al. Blood-retinal barrier permeability versus diabetes duration andretinal morphology in insulin dependent diabetic patients.Acta Opthalmol Copenh 1987, 65: 686-692.

45. Rechthand, E., Smith, Q.R., Latker, C.H. et al. Alteredblood-nerve barrier permeability to small molecules inexperimental diabetes mellitus. J Neuropath Exp Neurol1987, 46: 302-314.

46. Lorenzi, M., Karam, J.H., Mcllroy, M.B. et al. Increasedgrowth hormone response to dopamine infusion in insulindependent diabetic subjects. J Clin Invest 1980, 65: 146-153.

47. Bollinger, A., Frey, J., Jager, K. et al. Patterns of diffusionthrough skin capillaries in patients with long-term diabetes.N Engl J Med 1982, 307: 1305-1310.

48. Feldt-Rasmussen, B. Increased transcapillary escape rate ofalbumin in Type I (insulin-dependent) diabetic patients withmicroalbuminuria. Diabetalogia 1986, 29: 282-286.

49. Parving, H.-H. & Rossing, N. Simultaneous determinationof the transcapillary escape rate of albumin and IgG innormal and long-term juvenile diabetic subjects. Scand JClin Lab 1973, 32: 239-244.

50. Roztocil, K., Prerovsky, I. & Oliva, I. Capillary diffusioncapacity for 1-131 in the subcutaneous tissue of the lowerextremeties in patients with diabetes mellitus. Vasa 1976, 5:338-341.

51. Parving, H.-H., Noer, I., Deckert, T. et al. The effect ofmetabolic regulation on microvascular permeability to smalland large molecules in short-term diabetes. Diabetologia1976, 12: 161-166.

52. Waltman, S. Sequential vitreous fluorometry in diabetesmellitus: a marker of microvascular complications. TransAm Ophthalmol Soc 1984, 82: 827-849.

53. Tooke, J.E. The microcirculation in diabetes. Diabetic Med1987, 4: 189-196.

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


54. Landis, E.M. Microinjection studies of capillary bloodpressure in human skin. Heart 1930, 15: 209-228.

55. Williams, S.A., Wasserman, S., Rawlinson, D.W. et al.Dynamic measurement of human capillary blood pressure.Clin Sci 1988, 74: 507-512.

56. Shore, A.C., Sandeman, D.D. & Tooke, J.E. Nailfoldcapillary pressure in non-nephropathic diabetic patients ofmoderate disease duration: The effect ofangiotensin conver-ting enzyme inhibition by enalapril. British MicrocirculationSociety Meeting, April 1992, Birmingham University.

57. Tooke, J.E. A capillary pressure disturbance in youngdiabetics. Diabetes 1980, 29: 815-819.

58. Redisch, W., Rouen, L.R., Terry, E.N. et al. Microvascularchanges in early diabetes mellitus. Adv Metab Disorders1973, Suppl. 2: 383-390.

59. Tubiana-Rufi, N., Priollet, P., Levy-Marchal, C. et al.Detection by nailfold capillary microscopy of early mor-phologic capillary changes in children with insulin depen-dent diabetes mellitus. Diabetes Metab 1985, 15: 118-122.

60. Karlander, S.G., Hermansson, I.L. & Hellstrom, K. Nutri-tive toe skin capillaries in middle-aged patients with diabetesmellitus. Diabetes Metab 1985, 2: 165-169.

61. Kohner, E.M., Hamilton, A.M., Saunders, S.J. et al. Theretinal blood flow in diabetes. Diabetologia 1975,11: 27-33.

62. Felder, D., Russ, E., Montgomery, H. et al. Relationship inthe toe of skin surface temperature to mean blood flowmeasured with a plethysmograph. Clin Sci 1954, 13:251-257.

63. Wollersheim, H., Netten, P.M., Lutterman, J.A. et al.Ephedrine improves microcirculation in the diabetic neuro-pathic foot. Angiology 1989, Dec: 1030-1034.

64. Nitzan, M., Goss, D.E., Chagne, D. et al. Assessment ofregional blood flow and specific microvascular resistance inthe foot by means ofthe transient thermal clearance method.Clin Phys Physiol Meas 1988, 9: 347-352.

65. Holti, G. & Mitchell, K.W. Estimation of the nutrient skinblood flow using a non-invasive segmented thermal clear-ance probe. In P. Rolfe (ed.) Non-invasive PhysiologicalMeasurements, Vol. 1. Academic Press, London, 1979,pp. 113-123.

66. Scott, A.R., Bennett, T. & MacDonald, I.A. Diabetesmellitus and thermoregulation. Can J Physiol Pharmacol1987, 65: 1365-1376.

67. Corcoran, J.S., Owens, C.W.I. & Yudkin, J.S. Measurementof fingertip blood flow using thermal clearance reflectsanastomotic rather than nutrient blood flow. Clin Sci 1987,72: 225-232.

68. Eickhoff, J.H. & Jacobsen, E. Correlation oftranscutaneousoxygen tension to blood flow in heated skin. Scand J ClinLab Invest 1980, 40: 761-765.

69. Roberts, D.H., Tsao, Y. & Breckenridge, A.M. The repro-ducibility of limb blood flow measurements in humanvolunteers at rest and after exercise by using mercury-in-Silastic strain gauge plethysmography under standardizedconditions. Clin Sci 1986, 70: 635-638.

70. Greenfield, A.D.M. A simple water-filled plethysmographfor the hand or forearm with temperature control. J Physiol(Lond) 1954, 123: 62-64.

71. Whitney, R.J. The measurement of volume changes inhuman limbs. J Physiol (Lond) 1953, 121: 1-27.

72. Henriksen, O. Local sympathetic reflex mechanisms inregulation of blood flow in human subcutaneous adiposetissue. Acta Physiol Scand (Suppl) 1977, 450: 1-48.

73. Challoner, A.V.J. Photoelectric plethysmography forestimating blood flow. In P. Rolfe (ed.) Non-invasivePhysiological Measurements Vol. 1. Academic Press,London, 1979, pp. 36-60.

74. Nilsson, G.E., Tenland, T. & Oberg, P.A. Evaluation of alaser Doppler flowmeter for measurement of tissue bloodflow. IEEE Trans Biomed Eng 1980, 27: 597-604.

75. Watkins, D. & Holloway, G.A., Jr. An instrument tomeasure cutaneous blood flow using the Doppler shift oflaser light. IEEE Trans Biomed Eng 1978, 25: 28-33.

76. Stem, M.D., Lappe, D.L., Bowen, P.D. et al. Continuousmeasurements oftissue blood flow by laser-Doppler spectro-scopy. Am J Physiol 1977, 232: H441-448.

77. Tyml, K. & Ellis, C.G. Simultaneous assessment of red cellperfusion in skeletal muscle by laser Doppler flowmetry andvideomicroscopy. Int J Microcirc Clin Exp 1985, 4:397-406.

78. Tooke, J.E., Ostergren, J. & Fagrell, B. Synchronousassessment ofhuman skin microcirculation by laser Dopplerflowmetry and dynamic capillaroscopy. Int J Microcirc ClinExp 1983, 2: 277-284.

79. Tooke, J.E., Lin, P.-E., Ostergren, J. et al. Effects ofintravenous insulin infusion on skin microcirculatory flow inType 1 diabetes. Int J Microcirc Clin Exp 1985, 4: 69-83.

80. Tooke, J.E. & Rayman, G. The investigation of foot skinmicrocirculation in diabetes mellitus. In: Spence, V.A. &Sheldon, C.D. (eds) Practical Aspects of Skin Blood FlowMeasurement. Conference Proceedings. BiologicalEngineering Society, London, 1985, pp. 73-77.

81. Rayman, G., Hassan, A. & Tooke, J.E. Blood flow in theskin of the foot related to posture in diabetes mellitus. Br JMed 1986, 292: 620-621 (reply to letter).

82. Rayman, G., Spencer, P.D., Smaje, L.H. et al. Relationshipofcutaneous blood flow to duration and control ofdiabetes.Int J Microcirc Clin Exp 1984, 3: 285 (Abstract).

83. Grunwald, J.E., Riva, C.E., Sinclair, S.H. et al. LaserDoppler velocimetry study of retinal circulation in diabetesmellitus. Arch Ophthalmol 1986, 104: 991-996.

84. Goodman, A.H., Guyton, A.C., Drake, R. et al. A televisionmethod for measuring capillary red cell velocities. J ApplPhysiol 1974, 37: 126-130.

85. Intaglietta, M., Silverman, N.R. & Tompkins, W.R. Capil-lary flow velocity measurements in vivo and in situ bytelevision methods. Microvasc Res 1975, 10: 165-169.

86. Chittenden, S.J., Coleridge Smith, P.D., Lefford, F. et al. Animproved system for measuring capillary red cell velocitiesby video microscopy incorporating an automated vesseltracking facility. Int J Microcirc (Clin Exp) 1990,9: p. 135H(Abstract).

87. Chittenden, S.J. & Coleridge Smith, P.D. Measurement ofblood cell movement in the capillaries. Binary Comp Micro-biol 1991, 3: 107-110.

88. Tyml, K. & Sherebrin, M.H. A method for on-line measure-ment of red cell velocity in microvessels using computerizedframe-by-frame analysis of television images. Microvasc Res1980, 20: 1-8.

89. Tyml, K. & Ellis, C.G. Evaluation of the flying spottechnique as a television method for measuring red cellvelocity in microvessels. Int J Microcirc Clin Exp 1982, 1:145-155.

90. Wayland, H. & Johnson, P.C. Erythrocyte velocity measure-ment in microvessels by a two-slit photometric method. JAppl Physiol 1967, 22: 333-337.

91. Fagrell, B., Fronek, A. & Intaglietta, M. A microscope-television system for studying flow velocity in human skincapillaries. Am J Physiol 1977, 233: H318-321.

92. Katz, M.A. & Janjan, N. Forearm hemodynamics andresponses to exercise in middle-aged adult-onset diabeticpatients. Diabetes 1978, 27: 726-731.

93. Poulsen, H.L. & Nielsen, S.L. Water filtration ofthe forearmin short- and long-term diabetes mellitus. Diabetologia 1976,12: 437-440.

94. Rayman, G., Hassan, A. & Tooke, J.E. Blood flow in theskin of the foot related to posture in diabetes mellitus. Br JMed 1986, 292: 87-90.

95. Cheatle, T.R., McMullin, G., Farrer, J. et al. Skin damage inchronic venous disease: does an oxygen diffusion barrierreally exist? J Roy Soc Med 1990, 83: 493-494.

96. Breuer, H.-W.M., Breuer, J. & Berger, M. Transcutaneousoxygen pressure measurements in type I diabetic patients forearly detection of functional microangiopathy. Eur J ClinInvest 1988, 18: 454-459.

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/


97. Huch, R., Lubbers, D.W. & Huch, A. Reliability oftranscutaneous monitoring of arterial PO2 in newborninfants. Arch Dis Childhood 1974, 49: 213-218.

98. Mani, R., Gorman, F.W. & White, J.E. Transcutaneousmeasurements of oxygen tension at edges of leg ulcers:preliminary communication. J Roy Soc Med 1986, 79:650-654.

99. McCollum, P.T., Spence, V.A. & Walker, W.F. Oxygeninhalation induced changes in the skin as measured bytranscutaneous oxymetry. Br J Surg 1986, 73: 882-885.

100. Hauser, C.J. & Shoemaker, W.E. Use oftranscutaneous PO2regional perfusion index to quantify tissue perfusion inperipheral vascular disease. Ann Surg 1983, 197: 337-343.

101. Eickhoff, J., Ishihara, S. & Jacobsen, E. Effect ofarterial andvenous pressures on transcutaneous oxygen tension. ScandJClin Lab Invest 1980, 40: 755-760.

102. Wyss, C.R,. Matsen, F.A. III, King, R.V. et al. Dependenceof transcutaneous oxygen tension on local arteriovenouspressure gradient in normal subjects. Clin Sci 1981, 60:499-506.

103. Eickhoff, J., Ishihara, S. & Jacobsen, E. PaO2 by skinelectrode. Lancet 1979, ii: 1188-1189.

104. Falstie-Jensen, N., Spaun, E., Brochner-Mortensen, J. et al.The influence of epidermal thickness on transcutaneousoxygen pressure measurements in normal persons. Scand JClin Lab Invest 1988, 48: 519-523.

105. Fagrell, B. Microcirculatory disturbances - the final causefor venous leg ulcers? VASA 1982, 11: 101-103.

106. Franzeck, U., Bollinger, A., Huch, R. et al. Transcutaneousoxygen tension and capillary morphologic characteristicsand density in patients with chronic venous incompetence.Circulation 1984, 70: 806- 811.

107. Kobbah, A.M., Ewald, U. & Tuvemo, T. Impaired vascularreactivity during the first two years ofdiabetes mellitus afterinitial resolution. Diabetes Res 1988, 8: 101-109.

108. Dodd, H.J., Sarkany, I. & Gaylarde, P.M. Skin oxygentension in venous insufficiency of the lower leg. J Roy SocMed 1985, 78: 373-376.

copyright. on M


http://pmj.bm

j.com/

Postgrad M


ownloaded from

http://pmj.bmj.com/

investigations in diabetes mellitus · activeisotopessuchas'33XeandNal31Icanbeused to...

Documents

Transcript of investigations in diabetes mellitus · activeisotopessuchas'33XeandNal31Icanbeused to...