**3. Epidemiology of hypertension**

Arterial hypertension (HT) refers to a permanently and abnormally elevated arterial blood pressure . Arterial blood pressure (BP) corresponds to the force exerted by the circulating blood on the walls of blood vessels, and constitutes one of the cardinal vital clinical signs (Nichols WW. and others 2011). Hypertension can be classified either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found to explain a patient's condition. Secondary hypertension indicates that the high blood pressure is a result of (i.e., secondary to) another condition, such as kidney disease or tumours (pheochromocytoma among others). In current usage, the word "hypertension" once used without a qualifier will refers to essential systemic, arterial hypertension.

According to the World Health Organization (WHO) (World Health Organization and others 2004), hypertension is one of 7 diseases composing the entity of "cardiovascular diseases" (CVDs). This entity list includes, besides hypertension, coronary heart disease, cerebrovascular disease, peripheral artery disease, rheumatic heart disease, congenital heart disease and heart failure (Lopez and others 2006; World Health Organization and others 2004). By its target organ damage (TOD) hypertension remains an important cause of coronary heart disease, cerebrovascular disease, peripheral artery disease, and heart failure, which counts together with congenital heart disease for more than 75% of the CVDs morbimortality worldwide. The epidemiology of hypertension is therefore linked to CVDs and within this chapter, is considered both as a disease and as a risk factor for other CVDs.

Cardiovascular diseases, especially hypertension and related risk factors are of real health concern worldwide (Lawes and others 2008). Currently, the majority of hypertensive people live in developing regions (Kearney and others 2005), where their number is presumed to increase in coming decades (Kearney and others 2005), which inevitably will lead to a higher burden of cardiovascular diseases (Kearney and others 2005; Murray and Lopez 1997). Within a context of limited data on the burden of hypertension and other chronic diseases in many developing countries (Murray and Lopez 1997), those diseases are very often considered as uncommon and therefore they are rarely addressed by policy makers (Unwin and others 2001) who are very often focused on a well described predominance of infectious diseases in these regions (Unwin and others 2001).

Nevertheless, hypertension should be considered of great economic importance also in developing countries and regions like in Latina America, South Asia and sub-Saharan Africa, because it is frequently underdiagnosed, and frequently undertreated, as patients often cannot afford treatment. In such situations, the complications of hypertension are

care settings, particularly in low resource settings. The access to medicines is highly driven by the availability and the cost of these drugs and strongly influences the prescription and usage patterns which in the end affect control of blood pressure(Twagirumukiza and others 2010). The rational use of available resources and the integration of the management strategies at primary health care level (De Maeseneer J 2009) have been advocated as key point of

The aim of this chapter summarize the current knowledge on the use of antihypertensives in primary care and to provide an update to prescribers and health professionals in their daily questions about whom-and-how to treat –as far as arterial hypertension is concerned.

Arterial hypertension (HT) refers to a permanently and abnormally elevated arterial blood pressure . Arterial blood pressure (BP) corresponds to the force exerted by the circulating blood on the walls of blood vessels, and constitutes one of the cardinal vital clinical signs (Nichols WW. and others 2011). Hypertension can be classified either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found to explain a patient's condition. Secondary hypertension indicates that the high blood pressure is a result of (i.e., secondary to) another condition, such as kidney disease or tumours (pheochromocytoma among others). In current usage, the word "hypertension" once used

According to the World Health Organization (WHO) (World Health Organization and others 2004), hypertension is one of 7 diseases composing the entity of "cardiovascular diseases" (CVDs). This entity list includes, besides hypertension, coronary heart disease, cerebrovascular disease, peripheral artery disease, rheumatic heart disease, congenital heart disease and heart failure (Lopez and others 2006; World Health Organization and others 2004). By its target organ damage (TOD) hypertension remains an important cause of coronary heart disease, cerebrovascular disease, peripheral artery disease, and heart failure, which counts together with congenital heart disease for more than 75% of the CVDs morbimortality worldwide. The epidemiology of hypertension is therefore linked to CVDs and within this chapter, is considered both as a disease and as a risk factor for other CVDs.

Cardiovascular diseases, especially hypertension and related risk factors are of real health concern worldwide (Lawes and others 2008). Currently, the majority of hypertensive people live in developing regions (Kearney and others 2005), where their number is presumed to increase in coming decades (Kearney and others 2005), which inevitably will lead to a higher burden of cardiovascular diseases (Kearney and others 2005; Murray and Lopez 1997). Within a context of limited data on the burden of hypertension and other chronic diseases in many developing countries (Murray and Lopez 1997), those diseases are very often considered as uncommon and therefore they are rarely addressed by policy makers (Unwin and others 2001) who are very often focused on a well described predominance of infectious

Nevertheless, hypertension should be considered of great economic importance also in developing countries and regions like in Latina America, South Asia and sub-Saharan Africa, because it is frequently underdiagnosed, and frequently undertreated, as patients often cannot afford treatment. In such situations, the complications of hypertension are

improving hypertension treatment (Twagirumukiza and Van Bortel 2011).

without a qualifier will refers to essential systemic, arterial hypertension.

**3. Epidemiology of hypertension** 

diseases in these regions (Unwin and others 2001).

more frequent and more severe: mainly heart failure (Mensah 2003) and stroke (Mufunda J and others 2006). In addition if developing world inhabitants survive to adulthood, hypertension-related disease may be the major cause of premature mortality (Twagirumukiza and others 2009b). The prevalence of hypertension has been well described worldwide (Kearney and others 2005) and in sub-Saharan Africa (Twagirumukiza and others 2011). The current figures and their projections remain overwhelming. Currently around 972 million people have hypertension worldwide (rising up to 1.6 billion in 2025) and more than 65% of them are in developing countries (Kearney and others 2005). The 2008 number of hypertensives in sub-Saharan Africa is estimated at 74.7 million (increasing by 68.0% in 2025(Twagirumukiza and others 2011)).The prevalence of hypertension in this region is estimated at 16.2%, being higher in urban than in rural regions (Twagirumukiza and others 2011). This prevalence adjusted to WHO standard population is similar to the prevalence in western countries (Table 1).

Table 1 shows that although the prevalence of hypertension was lower in sub-Saharan Africa than in England and USA, the prevalence of hypertension adjusted to the WHO standard population was higher in sub-Saharan Africa than in England and tended to be higher than in USA. However, the analysis of age-specific prevalence data shows that the hypertension prevalence is higher at younger ages (up to 35 years) in sub-Saharan Africa compared to the western countries, indicating that hypertension starts at earlier age in sub-Saharan Africa. The prevalence in old people is lower in sub-Saharan Africa than in western country. The plausible explanation is linked to low accessibility to treatment: by lacking adequate treatment people with hypertension at younger age died in earlier ages (around 45-54 years). People with hypertension at older age are new cases or survivors.

There are evidences (Twagirumukiza and others 2011) of a clear difference in hypertension prevalence between countries. Different factors like diet habits (i.e. salt consumption) and genetic predisposition may play a role. As expected the prevalence of hypertension also increases with age and that prevalence was 50.7% higher in urban than in rural area. The influence of urbanization on hypertension was more pronounced in males than in females. These observations in rural versus urban areas are in line with other recent reports (Opie and Seedat 2005) reporting urban prevalence 1.5 to 2 times higher than rural ones. This difference can be influenced by the habits in rural which are dominated by routine field work as compared to urban lifestyle with more consumption of energy rich foods and a decrease in energy expenditure through less physical activity (Opie and Seedat 2005). However, modernisation (Dominguez and others 2006) may also transform rural settings themselves such as increasing use of automobiles leading to a decrease in physical activity, increasing overweight and obesity and more consumption of salt (Mufunda J and others 2006; Reddy and Yusuf 1998) and tobacco (Jha P and Chaloupka F 1999).

In sub-Saharan Africa setting, hypertension occurs earlier among adults of working age and its complications strike people at the top of their economic activity (Gaziano 2005; Twagirumukiza and others 2009b). Apart from the consequences on the quality of individual health, this leads to a large impact on a developing country's economic viability. In South Africa, for example, 2% to 3% of the country's gross national income, or roughly 25% of South African healthcare expenditures, was devoted to the direct treatment of cardiovascular disease (CVD) (Gaziano 2005; Pestana and others 1996).

The Use of Antihypertensive Medicines in Primary Health Care Settings 135

The definition of hypertension is then based on the potential of blood pressure to become a risk for cardiovascular events (Khosla and Black 2006). But this evaluation of potential risk has been improving in time and cut-offs have been lowered progressively. Previously, hypertension started at a cut-off SBP/DBP value of 160/95 mmHg, whereas the current standard is 140/90 mmHg. The current definition of hypertension which is unanimously agreed on by USA Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC7)(Chobanian and others 2003), European Society of Hypertension (ESH) and of the European Society of Cardiology (ESC)(Mancia and others 2007) and World Health Organization (WHO)(Chalmers and others 1999) is : **SBP ≥ 140mmHg and/or DBP ≥ 90mmHg and/or being on blood pressure lowering medication**(Chalmers and others 1999; Chobanian and others 2003; Mancia and others 2007). These cut-off values are even lower in high risk population (diabetes or renal failure). Different thresholds have been given for

Situations **SBP DBP**  Office or clinic 140 90 Ambulatory 24-hour 125–130 80 Day 130–135 85 Night 120 70 Home 130–135 85 Table 2. Different Blood pressure thresholds (mmHg)(Mancia and others 2007)

<120/80 - Normal Optimal 120-129/80-84 - Pre-hypertension Normal 130-139/85-89 - High normal

In daily practice, the blood pressure has also been splitted up into grades to help management. In this chapter, the most recent (2007) classification (Mancia and others 2007)

140-159/90-99 Hypertension grade 1 Hypertension stage 1 Hypertension grade 1 (mild)

≥180/110 Hypertension grade 3 Hypertension grade 3 (severe) \*\* ≥140/<90 - - Isolated systolic hypertension

Table 3. Recent classifications and staging of Systolic (SBP) / Diastolic (DBP) Blood Pressure

(moderate)

160-179/100-109 Hypertension grade 2 Hypertension stage 2 Hypertension grade 2

JNC-7: the Seventh report of the Joint National Committee on prevention, detection, evaluation, and treatment of high blood pressure (JNC-7)(Chobanian and others 2003). ESH/ESC: the European Society of Hypertension – European Society of Cardiology(Mancia and others 2007). WHO/ISH: the World Health Organization/ International Society of Hypertension(Whitworth 2003). Note that hypertension is defined as SBP/DBP of 140/90 mmHg according to the three recommendations(Chemla 2006).When a patient's systolic and diastolic blood pressure fall into different categories, the higher category should apply.

**WHO/ISH (2003) JNC-7 (2003) ESH/ESC (2007)** 

different types of measurements (Table 2).

will be used as a reference.

**SBP/DBP (mmHg)** 

levels


**[a]** Age range for USA prevalence starts from 18 years, for England are from 16 years and for sub-Saharan Africa are from 15 years; **[1]** Results from a meta-analysis on the population-based studies(Twagirumukiza and others 2011); **[2]** Results from the Health Improvement Network (THIN) database & Health Survey for England (HSE)(MacDonald and Morant 2008); **[3]** NHANES III continuous(Fields and others 2004); **[4]** WHO standard population adjusted prevalence; **NS:** Not statistically significant \*sub-Saharan Africa is statistically higher.

Table 1. Comparison between sub-Saharan Africa pooled data and developed countries surveys.
