could reduce blood pressure, decrease the rate of progression of blood pressure to hypertensive levels with age or prevent hypertension entirely.118
2.2.2 THE BURDEN OF HYPERTENSION
Hypertension which is considered to be one of the most prevalent and serious risk factors for cardiovascular disease, constitutes about 40% of all cardiovascular diseases.119 At the same time, it doubles the risk of cardiovascular diseases.120 According to Khatib et al121, for all hypertensive persons the risk of developing cerebrovascular disease is "continuous, consistent and independent of other risk factors". Thus, the higher the blood pressure, the higher the risk of developing complications. Hypertension is probably the most important public health problem in developed countries and implicated for rising morbidity and mortality in Africa.122
It is estimated that with good blood pressure control, 250000 deaths per year from complications such as stroke and kidney could be prevented in Africa.123
A study done by Kearney et al on Global burden of hypertension, indicates that more than a quarter of the world’s adult total population (which is nearly one billion) had hypertension in 2000, and that this proportion will increase to 29% (1·56 billion) by 2025.124 Additionally, overall prevalence of hypertension increases consistently with age in all world regions.
Data from the National Health and Nutrition Examination Survey (NHANES) conducted between 2005 and 2006 showed that one in three adults in the United States have hypertension.
It is estimated to be the same as 29% of the adult population; however the percentage is likely to continue to increase, primarily because of the aging of the population.125
In various regions of Africa, studies on hypertension prevalence, awareness and risks factors have also been conducted. It is estimated that hypertension affects 20 million people in Africa.126,127
In sub Saharan Africa, hypertension has also emerged as a serious public health problem.
Effects of westernization, urbanization, changes in dietary patterns and sedentary lifestyle are
among the factors fuelling the epidemic of hypertension in the sub-Saharan Africa128. More recently in Nigeria, various studies have tried to give a picture of hypertension prevalence amongst different population groups and regions in the country.
In Northwest Nigeria, Sani et al in a hospital-based cross-sectional descriptive study conducted in Katsina, reported a prevalence of 25.7% among 300 subjects who were consecutively recruited.129Isezuo et al (also in Northwest Nigeria) reported a prevalence of 24.8% for hypertension in a community based cross-sectional study involving 782 Fulanis and Hausas in Sokoto who were recruited by multi-stage sampling technique.130
In Northeast Nigeria, Kolo et al reported a prevalence rate of 23.7% in a hospital-based retrospective cohort study carried out in a tertiary hospital at Bauchi to identify hypertension related admissions among 3108 patients admitted over one year period.131
In, Southwest Nigeria, Adedoyin et al reported a prevalence of 36.6% for hypertension in a cross-sectional survey of 2,097 adults living in a semi-urban community of Ile-Ife who were selected using multi-stage sampling technique.132 In another rural community in Southwest Nigeria, Oladapo et al reported prevalence of 20.8%.133 In a rural community in South-south Nigeria, Omuemu et al also reported a prevalence rate of 20.2% for hypertension in a community-based cross-sectional study involving 590 respondents.134 In a rural community in Southeast Nigeria, Ahaneku et al reported a prevalence of 44.5% from a sample of 218 adults aged 18years and above.135 In another rural community in Southeast Nigeria, Onwubere et al also reported a prevalence of 46.4% in a study involving 858 subjects aged between 40 and 70 years.136 In Imo state where FMCO is located, Mbah et al reported a prevalence of 32.5% in a community-based cross-sectional survey involving 200 adults aged between 40 and 60 years residing in Ahiazu Mbaise Local Government Area of Imo state.137
The seriousness of hypertension as a global public health problem is evident by its high prevalence and associated increase in cardiovascular complications in virtually all countries of
the world. The burden of hypertension is better appreciated when the complications of this disease are considered.
2.2.3 AETIOLOGY OF HYPERTENSION
In more than 95% of cases, a specific underlying cause of hypertension cannot be identified and such patients are said to have essential hypertension.121 When there is no identifiable cause of hypertension, it is most often the result of complex interactions between multiple genetic and environmental factors, including diet (high salt intake), heavy consumption of alcohol, obesity, lack of exercise and impaired intrauterine growth.122 In contrast, approximately 5% of patients with hypertension have identifiable specific causes revealed by history, physical examination, and routine laboratory tests.121 This group of people are said to be having secondary hypertension. In particular, secondary hypertension should be suspected in patients in whom hypertension develops at an early age, those who first exhibit hypertension when over age 50 years, or those previously well controlled who become refractory to treatment.110 Causes of secondary hypertension include genetic syndromes, renal disease, renal vascular hypertension, primary hyperaldosteronism, Cushing’s syndrome, pheochromocytoma, coarctation of the aorta (uncommon), hypertension associated with pregnancy, estrogen use, chronic use of non-steroidal anti-inflammatory drugs (NSAIDs) among others.138
2.2.4 DIAGNOSIS OF HYPERTENSION:
A decision to embark upon anti-hypertensive therapy effectively commits the patients to life-long treatment, so it’s vital that the blood pressure (BP) readings on which this diagnosis is based are as accurate as possible.122 Exercise, anxiety, discomfort and unfamiliar surroundings can all lead to a transient rise in BP. Therefore to appropriately measure the blood pressure, the patient should sit in a chair in a quiet room for 5 minutes with his feet flat on the floor, his back supported, and his arms relaxed and supported at the level of the heart.118 The size of the cuff bladder should be at least 80% of the size of the patient’s arm. Two measurements should be
made on each arm, averaged and the readings shared with the patient. Hypertension is based on the average of at least two readings taken at each of two or more visits after an initial screening.122 High blood pressure or hypertension (HBP) is established when two readings have an SBP greater than or equal to 140 mmHg and/or a DBP greater than or equal to 90mmHg.
113-115 This criterion does not apply to patients with a markedly elevated BP and/or in those with evidence of end organ damage.114
Sometimes, BP measurements can give an unrepresentative high value particularly when performed in a health facility or by a doctor. This has been termed ‘white coat’ hypertension and as many as 20% of patients with apparent hypertension in the clinic may have a normal BP when it is recorded by a automated devices used in their own homes.122 A series of automated ambulatory BP measurement obtained over 24 hours or longer provides a better profile than a limited number of clinic readings.122
2.2.5 TREATMENT OF HYPERTENSION:
Goal of Therapy: In hypertensive patients, the primary goal of therapy is to achieve maximum reduction in cardiovascular and renal morbidity and mortality. This requires the treatment of both the raised BP and the associated reversible risk factors.
The guideline for treatment: The most current guideline for treatment of hypertension recommends both lifestyle modification and the use of antihypertensive agents. The effective management of hypertension requires making the patients understand the disease and its complications so as to ensure good compliance with treatment. They should be informed that Hypertension has no cure and that management is life-long and involves both non-drug and drug therapy.115 Non-drug therapy is indicated in all patients with hypertension. This involves lifestyle modifications which help to lower BP, control other risk factors and reduce the number or the doses of antihypertensive drugs. The lifestyle measures that are widely recognized and
recommended are:- smoking cessation, weight reduction (and weight stabilization), reduction of excessive alcohol intake, regular physical exercise, reduction of salt intake, increase in fruit and vegetable intake and decrease in intake of saturated and total fat.139
Drug therapy: This involves the rational use of anti-hypertensive agents: Five major classes of antihypertensive agents exist; thiazide diuretics, calcium antagonists (CCB), Angiotensin Converting Enzyme Inhibitors (ACEI), angiotensin receptor blockers (ARBs) and ß-blockers (BB) which are suitable for the initiation and maintenance of antihypertensive treatment, alone or in combination.122 The initiation of therapy with more than one drug increases the likelihood of achieving BP goal in a more timely fashion and at lower doses of the component agents, resulting in fewer side effects.140,141The choice of a specific drug or a drug combination should take into consideration the following: the previous favourable or unfavourable experience of the individual patient with a given class of antihypertensive agent, the presence of a compelling indication (ie sub clinical organ damage, clinical CV disease, renal disease or diabetes) which may be more favourably treated by some drugs than others.138 Other factors to consider include:
The presence of other disorders that may limit the use of particular classes of antihypertensive drugs and the cost of drugs; either to the individual patient or to the health provider. However, cost considerations should never predominate over efficacy, tolerability and protection of the individual patient. Attention should also be given to side-effect of the drug, because it is the most important cause of non-adherence. Drugs which exert their antihypertensive effect over 24 hours with a once-a-day administration should be preferred because a simple treatment schedule favours adherence. Once antihypertensive drug therapy is initiated, patients should return at intervals for follow-up, for refill when medications are exhausted and possible adjustment of medications until the BP goal is reached.
Recently, the report of the JNC 8 which was a product of an evidence-based approach drawn from randomized controlled trials recommends as follows:142 That there is strong evidence to
support treating hypertensive persons aged 60 years and above to a target BP of less than 150/90mmHg. (2) That a BP goal of less than 140/90mmHg for hypertensive persons younger than 60 years is recommended based on expert opinion. They also recommended the same BP goal for hypertensive adults with diabetes or chronic kidney disease (CKD) as for the general hypertensive population younger than 60 years. This is in contrast to the initial recommendation by JNC 7 of a target BP of below 140/90mmHg for all adult hypertensive patients and
<130/80mmHg in patients with diabetes and high risk patients (such as those having stroke, myocardial infarction, renal dysfunction, proteinuria etc). The recent report also recommended that drug treatment can be initiated with an ACEI, ARB, CCB or thiazide-type diuretic in the nonblack hypertensive population, including those with diabetes while in the black hypertensive population, including those with diabetes, a CCB or thiazide-type diuretic can be used as initial therapy. The report however concluded that the recommendations are not a substitute for clinical judgment and that decisions about care must be patient-centered.142
2.2.6 COMPLICATIONS OF HYPERTENSION
Complications of hypertension are usually accelerated by long-standing uncontrolled blood pressure. These complications are either due to consequent changes in the vasculature and the heart or due to atherosclerosis. They include:
Hypertensive cardiovascular disease: Cardiac complications are the major causes of morbidity and mortality in primary hypertension, and preventing them is a major goal of therapy.121For any level of blood pressure, its presence is associated with incremental cardiovascular risk.
Echocardiography-reported left ventricular hypertrophy is a powerful predictor of prognosis.
However, hypertensive left ventricular hypertrophy regresses with therapy and is most closely related to the degree of systolic blood pressure reduction.138
Hypertensive cerebrovascular disease and dementia: Hypertension is the major predisposing cause of hemorrhagic and ischemic stroke. Cerebrovascular complications are more closely
correlated with systolic than diastolic blood pressure.138 The incidence of these complications is markedly reduced by antihypertensive therapy. Preceding hypertension is associated with a higher incidence of subsequent dementia of both vascular and Alzheimer types. Effective blood pressure control may reduce the risk of development of cognitive dysfunction later in life, but once cerebral small vessel disease is established, low blood pressure might exacerbate this problem.138
Hypertensive renal disease: Chronic hypertension leads to nephrosclerosis, a common cause of renal insufficiency; aggressive blood pressure control attenuates the process. Hypertension also plays an important role in accelerating the progression of other forms of renal disease, most commonly diabetic nephropathy.138
Atherosclerotic complications: Hypertension is a contributing factor in many patients with dissection of the aorta.110
Hypertensive retinopathy: Hypertension causes retinopathies that may progress to blindness.
In severe cases, papilledema occurs.122
CHAPTER THREE
MATERIALS AND METHOD