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associated with development of PAD52 as observed in this study. Hypertensives, in the Framingham study follow-up, were observed to have a 2.5 to 4 fold increased risk of PAD.52,149
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Though the study of Fowkes and his colleaques was on cross-sectional survey conducted on age-stratified subjects of men and women aged 55 to 74years and ours was on much wider age range, the clinical diagnosis and assessment of severity of intermittent claudication, generally, is not always reliable. This is because patients may not volunteer the history, and also there are other causes of calf pain such as deep venous thrombosis. It may also be that our subjects could ‘walk through’ their pain hence, to them, the pain experienced is not significant enough to tell their physicians. Therefore until PAD becomes extensive and severe it is probably largely asymptomatic and hence unreported.
Palpation of peripheral pulses has been used as a clinical tool to assess peripheral occlusive arterial disease in diabetic and non-diabetic patients particularly when intermittent claudication is present. However, it may be difficult to interpret the significance of diminished peripheral pulses when symptoms are not present. In this study, clinical palpation of pulses in our study showed a PAD prevalence of 25.3%, and sensitivity, specificity, positive and negative predictive values of 29.5%, 66.7%, 56.7%
and 39.7% respectively. The reason for the lower sensitivity of the palpation method could be due to variation in ambient temperature, anatomical location, congenital absence of the dorsalis pedis and calcification. Congenital absence of dorsalis pedis having been documented in 10% of white population could contribute significantly to low prevalence.151 But, in this study no case of congenital absence was found.
Ankle-brachial pressure index (ABPI) had low sensitivity (23.2%) but high specificity (85.4%) in our study. The prevalence of PAD based ABPI is 19.7%. Though the ABPI is a simple, noninvasive bedside tool for diagnosing PAD, it provides a semi-quantitative and objective measure of the severity of symptomatic PAD, and allows for
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identification of asymptomatic PAD. It may however give altered readings in calcified or incompressible arteries such as seen in elderly patients, patients with diabetes or patients in end-stage renal failure requiring dialysis or in subclavian artery stenosis. Although the ABPI is a gold standard in the early diagnosis of PAD and assessment of the severity of haemodynamic impairment of arterial blood flow in lower extremities, its diagnostic value, as earlier written, is lower in the presence of arterial calcification. 135,136 It is this inadequate and late recognition/detection of PAD that places many patients at risk of its complications, including ischaemia, ulceration, gangrene, limb loss, and/or increased cardiovascular morbidity and mortality.152 McDermott et al153 reported the sensitivity of ankle-brachial pressure index (ABPI) in the diagnosis of PAD to be 90% with a corresponding 98% specificity for detecting haemodynamically significant stenoses (>50%). Norgren et al35 reported 90-95 percent sensitivity and 98 to 100 percent specificity for angiographically verified peripheral arterial stenosis while Doobay et al154 in their review of ABPI found the specificity of ABPI to be highly predictive of cardiovascular outcomes. In this present study we found a low sensitivity of 23.2%, and high specificity of 85.4% and positive and negative predictive values of 69.6% and 43.6% respectively for the use of ABPI to diagnose PAD. Prevalence is low and this may be due to high mean age of the study population since mean older age predisposes to arterial calcification, making the vessel less compressible hence giving falsely negative results. It could also be that patients were anxious, inappropriate gel, incorrect size of sphygmomanometer, inappropriate size of Doppler probe, releasing the sphygmomanometer too quickly, inadequate preparation and uncomfortable temperature
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which could cause inappropriately high blood pressure and produce falsely high or
‘normal’ ABPI. However, these were as much as possible prevented during the study In a study by Fowkes et al155 using both spectral waveform pattern and peak systolic velocity to assess PAD, they reported the sensitivity of 78%, specificity of 65%
and positive predictive value of only 19% in the diagnosis of PAD. However, spectral waveform pattern assessment of PAD in this study seems the best method only after intima-media thickness. Blood flow spectral pattern gave a prevalence of 33.9% in our study. It has moderately high sensitivity of 54.2% and very high specificity of 94.4% and positive and negative predictive values of 93.1% and 59.7% respectively.
The prevalence of PAD using peak systolic velocity measurement in this study was 2.0% with a very low sensitivity of 2.4% but very high specificity of 94.4%, positive predictive value of 93.1% and negative predictive value of 59.7%. Studies had compared the duplex imaging of lower extremity arteriography to define its accuracy and a sensitivity of 77-92% and specificity of 92-98% were reported.156,157 The low sensitivity could be due to the degree of angulations of the probe because a doppler angle of 60 degrees or less is required to derive accurate velocity, a greater angle reduces and renders velocity measurement unreliable. However, this and other precautions were taken during our study.