NEON Assembly

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inaccurate measurements as a result of calcified or incompressible vessels (which would produce falsely elevated readings) especially in the diabetic and elderly patients. Also, the presence of a subclavian-artery stenosis (which could also falsely elevate the ankle–brachial index on the side of the stenosis).⁵⁰ Despite these limitations however, ankle-brachial index

measurement has been reported to have a sensitivity above 90% in contrast to intermittent claudication with a sensitivity of about 50%.^50,62 and a specificity of 95% for the diagnosis of peripheral arterial disease.⁵⁰ It has also been

reported to have marginal observer variability.⁶² In our study, the sensitivity and specificity of the historical method of assessing PAD were 45% and 94% respectively, and the sensitivity and specificity of the palpation method were 80% and 98% respectively with reference to the ankle-brachial-index.

History of intermittent claudication and palpation of peripheral pulses are indicators of peripheral arterial disease, and are relevant in clinical practice, but the use of ankle-brachial index may be more sensitive in detecting PAD.

5.4 RISK FACTORS FOR PERIPHERAL ARTERIAL DISEASE

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identification and possible treatment may be a cost-effective means of preventing peripheral arterial disease and its complications.

Previous studies ^34,55,57 indicate the association of PAD with both modifiable and non-modifiable risk factors. Modifiable risk factors include hypertension, hypercholesterolemia, diabetes mellitus, and smoking. Non

modifiable factors include age and sex. Other risk factors that are associated with an increased prevalence of PAD include race and ethnicity (African Americans and those of Hispanic origin are at higher risk), metabolic

syndrome, obesity, and levels of C-reactive protein, ß2-microglobulin, cystatin C, lipoprotein (a), and homocysteine.33,63,65,66 The most common risk factors that have been associated with PAD are advanced age, diabetes and

smoking.^55,63

Data from this study reveal that waist circumference (WC) values are significantly higher in PLWDM compared with controls. There is also a significant association between WC and PAD on regression analysis, with an eleven fold risk of developing peripheral arterial disease with increasing waist circumference (OR = 0.089, CI = 0.015-0.530). WC has been shown to be significantly associated with PAD and other cardiovascular diseases in previous report.⁶⁵

Waist circumference (WC) is a measure of central obesity (adiposity).

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Adipocytes function as an endocrine organ, and not just an energy depot, and adipocytes have been shown to play a substantial role in the pathogenesis and development of complications in obesity.^67,68 The adipocyte release cytokines such as the tumour necrosis factor (TNF) α, prothrombotic agents such as plasminogen activator inhibitor 1 (PAI-1), angiotensinogen, leptin and adiponectin.^69,70 These factors play a role in inflammation, coagulation and atherogenesis.^69,70 Obesity, especially abdominal, represented by WC is also associated with an atherogenic lipid profile, that is, increased low-density lipoprotein (LDL) cholesterol, very low-density lipoprotein, triglycerides and decreased high-density lipoprotein cholesterol.⁶⁹

Interleukin-6 (IL-6) one of the adiponectins secreted by adipocytes, increase the hepatic secretion of fibrinogen which may enhance

atherogenesis by increasing the likelihood of platelet cross-linking, increase fibrin clot formation and increase blood viscosity.⁷¹ IL-6 also modulates CRP production in the liver, and CRP may be a marker of a chronic inflammatory state,⁷⁰ which has been shown to predispose to atherosclerosis.

These may be some of the reasons why subjects with increased values of WC may contribute to increased prevalence of PAD.

The level of a non-traditional risk marker for inflammation, C-

reactive protein used in this study, was higher in PLWDM compared with

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controls. The study population was grouped, according to the American Heart Association and the Centers for Disease Control and Prevention guidelines, into CRP groups of <1mg/L, 1-3mg/L and >3mg/L which are interpreted as low, average and high relative vascular risks respectively.⁷² This

classification showed that more PLWDM are in the average and high

vascular risk groups compared with controls. CRP values > 10mg/L suggest acute-phase response from an underlying inflammatory disease or infection.⁷² None of the subjects in the study population had CRP value of >10mg/L (Range 0.01-6.62mg/L).

Regression analysis also showed that there is about two-fold risk of developing PAD with increasing levels of CRP (OR = 0.701, CI = 0.498 – 0.986). This finding is consistent with previous reports^34,66 demonstrating a significant association between CRP and PAD.

CRP is a marker of inflammation and inflammation characterizes all phases of atherothrombosis.^10,11,73 CRP is a circulating member of the pentraxin family, secreted primarily from the liver , but has been found in cells in the intima, particularly atherosclerotic intima.^10,11,73 However, more than simply a marker of inflammation, CRP may directly influence vascular vulnerability through several mechanisms, including enhanced expression of local adhesion molecules, increased expression of

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endothelial plasminogen activator inhibitor 1 (PAI-1), reduced endothelial nitric oxide bioactivity, altered LDL uptake by macrophages, and

co-localization with complement within atherosclerotic lesions.^10,11,73 All these may enhance formation and progression of atherosclerosis, and hence explain the rise in prevalence of PAD with increasing levels of CRP as noted in this study.

Data from this study after regression analysis also showed that advancing age may be a risk for PAD. Previous studies ^29,34,74 also

demonstrated this finding. The increased prevalence of PAD with advancing age may be explained by the fact that the incidence of other risk factors associated with atherosclerosis, such as diabetes^39,40 and hypertension⁴⁶ also increases with age. Also, the reduced incidence of atherosclerosis observed in women conferred by a favourable lipoprotein pattern in premenopausal women is lost after menoupause.⁷⁵ Physical inactivity, brought about by degenerative joint diseases and other cardiovascular disorders (such as coronary heart disease) may also indirectly increase the incidence of PAD by increasing its risk factors such as DM and hypertension. The above may therefore explain the higher prevalence of PAD with increasing age

observed in this study.

Male sex increased the risk of PAD in this study by more than four-

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fold (OR = 0. 224; CI = 0.064 – 0.787) with reference to females after regression analysis. Some studies ^25,74 also documented similar findings of higher prevalence of PAD in males compared with females. The reason for the increased prevalence of PAD in males may be due to the relatively higher HDL levels in women (especially premenopausal) compared with men.⁷⁵ The process of reverse cholesterol transfer may explain in part the apparent protective role of HDL against atherosclerosis, by ferrying

cholesterol from the vessel walls, thus augmenting peripheral catabolism of cholesterol.⁷³ HDL can also carry antioxidant enzymes that may reduce the level of oxidized phospholipids in atheromatous lesions, which might

enhance atherogenesis.⁷³

Correlation analysis showed a significant negative correlation between glycated haemoglobin (a measure of long-term glycaemic control) and PAD (r = - 0.191, p = 0.019). This indicate an inverse relationship between PAD (as measured by ABI) and glycated haemoglobin level. That is, the lower the ABI, the higher the glycated haemoglobin level. Glycated haemoglobin level was also significantly higher among the PLWDM who had PAD compared with PLWDM without PAD. This association between PAD and

hyperglycaemia has been found in several studies.31,74,76,77

The pathogenetic link between hyperglycaemia and PAD may be due

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to the fact that hyperglycaemia inhibits arterial endothelial nitric oxide (NO) production.² Hyperglycaemia inhibits production of nitric oxide by blocking endothelial nitric oxide synthase (eNOS synthase) activation and increasing the production of reactive oxygen species, especially superoxide anion (O²⁻), in endothelial and vascular smooth muscle cells. Superoxide anion directly quenches nitric oxide by forming the toxic peroxynitrite ion, which

uncouples eNOS by oxidizing its cofactor, tetrahydrobiopterin, and causes eNOS to produce superoxide (O²).⁷⁸

Nitric oxide potently dilates vessels, inhibits platelet activation, limits inflammation by reducing leukocyte adhesion to endothelium and migration into the vessel wall, and diminishes vascular smooth muscle cell

proliferation and migration, hence NO inhibit atherogenesis and protects the blood vessel.⁷⁸

Hyperglycaemia also potentiates atherogenesis by enhancing platelet derived growth factor- (PGDF) induced vascular smooth muscle cell

proliferation, and stimulates plasminogen activator inhibitor 1 (PAI-1)

production.² In addition hyperglycaemia, especially in the setting of insulin resistance may be associated with atherogenic diabetic dyslipidaemia with low HDL, high triglycerides and atherogenic, small dense LDL.⁷⁵

Hyperglycaemia also causes accumulation of advanced glycation end

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products associated with vascular damage.⁷³ These may thus explain the association between PAD and glycated haemoglobin level.

Smoking has been reported to be a common risk for PAD, 34,55,57,63

however, smoking was not found to be a risk factor in this study. The reason for this may be that few subjects in both the PLWDM (less than 15%) and the control groups (6%) ever smoked. Also, a dose-response relationship exists between pack-year history and PAD risk.⁶³ Most of the subjects that ever smoked, smoked less than 5pack-years. Also, none of the PLWDM still smoke (Table 2). Hence the fewer number of smokers and the minimal smoking dose in those that smoked may account for the absence of association between smoking and PAD.

The duration of Diabetes was longer in PLWDM who had PAD compared with those without PAD. In terms of drug usage (antilipids,

antihypertensives and antidiabetic drugs), there was no statistically significant difference between the PLWDM who had PAD and those who do

not have. Hence the effect of drug therapy may not explain the differences observed between PLWDM who had PAD and those without PAD.

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CHAPTER SIX

CONCLUSION AND RECOMMENDATION 6.1. CONCLUSION

1. The prevalence of peripheral arterial disease determined by

measurement of ankle-brachial index is significantly higher among PLWDM than controls.

2. The sensitivity and specificity of the historical method of assessing PAD were 45% and 94% respectively, and the sensitivity and specificity of the palpation method were 80% and 98% respectively with reference to the ankle-brachial-index.

3. Traditional risk factors for peripheral arterial disease such as hypertension, obesity, total serum cholesterol, serum low-density

lipoprotein, serum triglycerides and hyperglycaemia are significantly higher in people with peripheral arterial disease compared with people without peripheral arterial disease. .

4. Potential (non-traditional) risk factors for peripheral arterial disease such as total white cell count, lymphocyte count and C-reactive protein are significantly higher in people with peripheral arterial disease

compared with people without peripheral arterial disease.

5. Measure of central obesity (waist circumference) is significantly

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associated with peripheral arterial disease of lower limb.

6. C-reactive protein, a marker of inflammation, and a potential causative factor for atherosclerosis is significantly associated with peripheral arterial disease of the lower limb.

7. Males have higher risk of developing peripheral arterial disease than females.

8. The prevalence of peripheral arterial disease increases with advancing age.

9. There is significant inverse correlation between peripheral arterial disease and long-term measure of glycaemia (glycated haemoglobin).

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