Lucia B Pemble PhD BSc(Hons) DMU (Vascular)

Peripheral arterial disease (PAD) or chronic occlusive arterial disease produces symptoms dependent upon the location and severity of the lesion(s) and the adequacy of collateralisation. The earliest symptom of PAD is claudication which is reproducible ischemic leg pain induced by exercise and relieved by rest. The patient may describe either muscle pain, tightness, cramp, heaviness or fatigue. Claudication results from insufficient supply of blood and nutrients to the exercising muscles. Symptom onset may be accelerated by walking uphill and progression of the occlusive process may change the intensity and character of the symptoms described by the patient¹. When the occlusive process is extensive, concomitant with trauma and/or infection, and there is inadequate collateral, a decrease in tissue perfusion may result in the development of rest pain, ulceration/infarction of tissue or gangrene. PAD may be present for many years in a subclinical form. The symptoms of arterial obstruction develop only when there is approximately a 50% narrowing of the arterial lumen. The most frequent presenting symptom is intermittent claudication of the calf musculature². Diabetic patients are prone to small vessel disease and also frequently describe ankle and foot pain. In this group of patients differentiation of tissue ischaemia from diabetic neuropathy can be difficult. If the obstructive lesion(s) lie within the aorto-iliac or inflow region, claudication of the buttock, thigh or hip may occur as well as lower back pain. Bilateral proximal claudication with impotence is classic of the presentation of Leriche syndrome.

CONCLUSION
The non-invasive techniques described here, CW Doppler waveform analysis, segmental pressure measurement and exercise testing all have a valuable role in determining the presence of arterial occlusive disease within a patient. The waveforms and pressures are complementary for the interpretation of a pressure-reducing lesion, while exercise testing helps `unmask' a subcritical stenosis, not evident in the resting state.

Exercise testing is a functional test of the disability produced by the presence of occlusive arterial disease. It allows objective assessment of claudication distance and the disability produced by other concomitant medical problems eg ischemic heart disease and pulmonary dysfunction, which are not uncommon in this more elderly patient population.

Duplex ultrasound is widely used in the assessment of lower extremity arterial occlusive disease^10,15,16. Duplex provides anatomic information about the presence of lesion(s), the location of lesion(s) and the local velocity changes that occur through lesion(s). However duplex does not provide the same information as the aforementioned non-invasive techniques¹⁷. Duplex is complementary to these non-invasive tests, allowing precise anatomic localisation and characterisation of the disease which may be important in planning further therapy and invasive reconstructive intervention.

Many patients with PAD however, do not progress to any form of invasive intervention. What is required is a simple non-invasive test that identifies the presence of the disease, the approximate location and number of arterial segments involved along with objective evidence of the physiological impairment produced by the disease. More precise anatomic detail, as provided by duplex, is required only if invasive intervention is being considered. With conservative treatment, modification of risk factors and the institution of an exercise program, the disease is stabilised in many patients¹⁸. Repeating the CW Doppler waveforms and pressures, pre and post exercise after a period of medical therapy, a change in the ABI value will indicate if deterioration of the disease has occurred. While in controlled studies a change in ABI of >0.15 has indicated significant change in the disease status of a patient, Fischer et al (1997)¹⁹ report that in the clinical situation variability in ABI may be as large as 0.21. In conclusion, peripheral arterial occlusive disease produces symptoms related to arterial obstruction and altered regional haemodynamics. The assessment of the combined effects of obstruction and collateral compensation are suited to functional tests that measure regional haemodynamics as have been described above.

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