P. T. McCollum

Spectrophotometric measurements of haemoglobin saturation and concentration in skin during the tuberculin reaction in normal human subjects

A non-invasive technique employing light-guide spectrophotometry is described for the measurement of haemoglobin concentration and oxygenation in human skin. Measurements were carried out in the visible wavelength range (500-620 nm) and a series of experiments were carried out in vitro and in vivo in order to calibrate the system. Indices were derived for the measurement of relative haemoglobin concentration and absolute oxygen saturation. The technique was applied to measure the changes in these parameters occurring during the course of the tuberculin reaction in human skin. The results are compared with those from laser Doppler flowmetry and transcutaneous oxygen measurements which were carried out concurrently. Divergence between the intracapillary and tissue oxygenation during the course of the reaction provides evidence for the existence of increased diffusion resistance for oxygen; a model is proposed. The study demonstrates the potential clinical usefulness of light-guide spectrophotometry for the non-invasive investigation of tissue oxygen supply.

Relationship between abdominal aortic aneurysm wall compliance and clinical outcome: a preliminary analysis

BACKGROUND Aortic compliance, as measured by the pressure-strain elastic modulus (Ep) and stiffness (B), may allow a more precise estimate of abdominal aortic aneurysm rupture risk than size alone. AIM To determine the relationships between AAA compliance, size, growth, and clinical outcome. METHODS One-hundred and twelve patients with initially non-operated AAA (86 men, 26 women, mean age 73 years), recruited from five centres, underwent baseline compliance measurements and were then followed for a median of 7 (range 2-18) months; 85 patients underwent repeated measurements (median 3, range 2-5) 3-6-monthly over a median of 12 (range 3-18 months). RESULTS Seven patients have ruptured and 16 have undergone repair of non-ruptured AAA. AAA that ruptured had significantly lower Ep and B (more compliant). In AAA that ruptured or required repair there was an inverse relationship between diameter and Ep and B. In those undergoing repeated measurements AAA expansion was only associated with a significant increase in Ep and B in non-operated patients. CONCLUSIONS Baseline AAA compliance was significantly related to rupture and the future requirement for operative repair. Failure of compliance to increase with size may be a marker for rapid growth, developmental symptoms and rupture.

Exercise in Patients with Intermittent Claudication Results in the Generation of Oxygen Derived Free Radicals and Endothelial Damage

Peripheral vascular disease is a major cause of morbidity in Britain. Each year approximately 50,000 patients are admitted to hospital in Britain with a principal diagnosis of peripheral vascular disease and of these over 20,000 have major surgery, including amputations, with an operative mortality of about 10% (Department of Health and Social Security Office of Population Censuses and Surveys 1986). Intermittent claudication is the most common symptom of peripheral vascular disease (Dormandy et al, 1989) and is a symptom of cramp-like muscle pain, brought on by walking, relieved by rest and reproduced by further exercise. It may affect the calf, thigh or buttock muscle groups depending upon the level and degree of vascular obstruction. Intermittent claudication is caused by an inadequate blood supply to the exercising muscles of the lower limb, although the exact pathophysiological mechanism responsible for the symptom remains unknown (Lorentsen, 1973). Five per cent of men over 50 years suffer from intermittent claudication (Dormandy et al,1989). Claudication itself does not cause death, however, the mortality of claudicants is approximately three times that of age and sex matched individuals (Dormandy et al,1989), being about 50% after ten years (Dormandy et al, 1986). Seventy-five per cent of these deaths are due to cardiovascular disease, such as. myocardial infarction, cerebrovascular accidents and aortic aneurysms (Dormandy et al,1989). Paradoxically the disease seems to stabilise symptomatically in seventy-five per cent of patients soon after onset (Dormandy et al,1989) and few claudicants progress to limb threatening ischaemia (Cronenwett et al,1984).

Amputation level assessment using lightguide spectrophotometry

The aim of this experimental study was to investigate whether lightguide spectrophotometry in the visible wavelength range in skin could be used to predict stump healing viability in patients with critical lower limb ischaemia. Remission spectra recorded at two sites (medial and lateral) on the line of a proposed trans-tibial amputation (TTA) and at 10mm intervals along the leg were analysed to give haemoglobin oxygenation (SO2). Degree of tissue hypoxia (DTH) along the leg was defined as the percentage of values along the leg less than 10% SO2. DTH and mean SO2 values were compared with skin blood flow values ((I125) 4-Iodoantipyrine clearance technique) and clinical outcome of trans-tibial amputation, (TTA) or trans-femoral amputation (TFA), in 41 patients. SO2 histograms were also measured in 12 normal subjects for comparison. The results of the study allowed the establishment of criteria for the accurate prediction of flap healing potential. Successful TTAs all displayed a minimum mean SO2 at the medial and lateral measurement sites of 30%, together with a maximum degree of tissue hypoxia of 15% along the limb. The combination of these criteria gave a sensitivity and selectivity of 1.0 for prediction of a successful outcome of TTA.

Comparison of macro- and micro-lightguide spectrophotometric measurements of microvascular haemoglobin oxygenation in the tuberculin reaction in normal human skin

The changes in haemoglobin oxygenation (SO2) occurring in the tuberculin reaction in human skin were measured using macro- and micro-lightguide spectrophotometry and the results compared. A significant difference was found between the measurements from the respective instruments, demonstrating that the micro-lightguide technique measures only in the most superficial capillaries. Laser Doppler flux (LDF) and transcutaneous oxygen (tcpO2) measurements were also obtained concurrently. At the height of the reaction, heating did not significantly change SO2 or LDF, showing that the vessels in the skin were maximally vasodilated. Although SO2 was increased in the reaction, tcpO2 decreased. This suggests that the infiltrating cells may present a diffusion barrier to oxygen between the capillaries and the tissue cells. This study has shown that micro-lightguide spectrophotometry gives a local picture of intracapillary oxygen supply, which is useful in elucidating the pathophysiological changes occurring during chronic inflammation.

Aortic bifurcation reconstruction: Use of the memotherm self-expanding nitinol stent for stenoses and occlusions

AbstractPurpose: To assess the technical success, initial clinical outcome, and intermediate follow-up of the Memotherm nitinol self-expanding stent in aortic bifurcation reconstruction. Methods: Thirty-three patients (13 male, 20 female), mean age 64 years, were treated, who had symptoms classified by the Surgical Vascular Society/International Society of Cardiovascular Surgery (SVS/ICVS) classification as grade 2 in 11 (33%), grade 3 in 19 (58%) and grade 4 in 3 (9%) patients. Lesions were classified according to severity and type. Indications for placement of a Memotherm nitinol self-expanding stent were failed angioplasty in 14 (42%), chronic occlusions in 12 (37%), and complex stenoses in seven (21%) patients. Results: Sixty-seven stents were technically successfully placed in 66 aorto-iliac segments in 33 patients, with one major complication. Initial clinical outcome was iprovement in 25 (81%), no change in four (13%), and a worsening in two (6%) patients by Rutherford criteria. Mean early ankle/brachial pressure index (ABI) gain was 0.27 for occlusions and 0.05 for stenoses. Clinical follow-up was obtained in all patients, with retrospective angiographic follow-up in 28 (85%) at a mean of 16 months (range 12–26 months). The decrease in ABI and the decrease in angiographic luminal diameter at follow-up was determined as the “late loss.” The mean ABI late losses were −0.06, 0.00, and 0.09, and the mean angiographic late losses were 6.7%, 10% and 14% for occlusions, stenoses, and normal segments respectively. Primary clinical patency was 96%, primary angiographic patency was 89%, and secondary angiographic patency was 93%. Conclusion: The high technical success of stent placement, the low complication rates for aortic bifurcation reconstruction using the Memotherm self-expanding stent, and high clinical and angiographic patency maintained at intermediate follow-up support their use in aortic bifurcation reconstruction.

USE OF LIGHTGUIDE REFLECTANCE SPECTROPHOTOMETRY IN THE ASSESSMENT OF PERIPHERAL ARTERIAL DISEASE.

Peripheral vascular disease (PVD) is a major cause of morbidity in the Western World. Its most common manifestation is intermittent claudication which is a symptom of cramp-like muscle pain. It is brought on by walking, relieved by rest and reproduced by further exercise and it may affect the calf, thigh or buttock muscle groups depending on the site and severity of the disease. Approximately 5% of men over 50 years of age suffer from intermittent claudication1. It is caused by an inadequate blood flow through the muscle during exercise, although the exact pathophysiological mechanism responsible for the symptom is still unknown2.

MANAGEMENT OF ILIAC OCCLUSIONS WITH A NEW SELF-EXPANDING ENDOVASCULAR STENT

OBJECTIVES To determine the patency and acceptability of the Memotherm endovascular stent in the treatment of iliac arterial occlusions. MATERIALS AND METHODS Twenty-two patients (12 males and 10 females) underwent stenting of iliac occlusions of the aortoiliac bifurcation, the common iliac artery and the external iliac artery. All patients were reassessed at 3, 6 and 12 month intervals and then yearly to evaluate their symptoms and Doppler pressure measurements. Comparison was made with results from other studies treating iliac occlusions by angioplasty alone or combined with stenting. RESULTS Out of 22 patients, 21 had an immediate and sustained improvement over the whole of the follow-up period. The Ankle-brachial Index (ABI) increased from a mean value of 0.49 to 0.81 3-months postprocedure and improved to 0.85 at 12 months (paired t-test p < 0.001). At 6 and 12 months the stent patency remained at 95.5%, which compares favourably with other studies. There were four minor and one major complication associated with the stenting procedure. CONCLUSIONS The Memothern self-expanding stent is a useful, safe and effective device suitable for the majority of iliac occlusions. Further long-term evaluation is warranted to confirm its advantages over open surgery.

The effect of the transcutaneous electrode on the variability of dermal oxygen tension changes

Transcutaneous oxygen measurements (TCPO2) are being used increasingly for the assessment of tissue viability in the ischaemic limb. The major objective with such a technique is to determine the critical level of TCPO2 which defines the boundary between skin viability and non-viability. To be able to do this, an assumption is made that measurements from different centres using various TCPO2 sensors are comparable. This study shows that static and dynamic changes of TCPO2 (air to oxygen breathing) made with two commercially available instruments are not directly comparable. We suggest that the physical characteristics of present TCPO2 electrodes are not optimal for measurements on adult skin. TCPO2 measurements made in conditions of skin ischaemia should be interpreted with caution because the ratio of local oxygen demand to blood flow is such that the measurement may be underestimated by TCPO2 electrodes with a high oxygen consumption.

Laser Doppler Perfusion Imaging Compared with Lightguide Laser Doppler Flowmetry, Dynamic Thermographic Imaging and Tissue Spectrophotometry for Investigating Blood Flow in Human Skin

Lightguide laser Doppler flowmetry (LDFc) is widely used both in micro-circulatory research and in clinical blood flow studies (for a review, see Shepherd and Oberg, 1990). Despite the inability to measure blood flow in absolute terms with the method (flux values are quoted in volts), physiological challenges can be used in order to test local and sympathetic control of the microvascular flow (Khan et al., 1991).