Secondary Hypertension

Hypertension is a medical condition wherein the blood pressure stays higher than 140 over 90 mmHg.* When blood pressure remains elevated for an unknown cause, it is called primary (also known as essential or idiopathic) hypertension. On the other hand, high blood pressure as a result of another complication such as tumor, endocrine or kidney diseases it is called secondary hypertension.* Risk factors which are likely to contribute to high blood pressure include age (more prone to people age 60 years and above), weight/size (obesity), sex (men are mostly diagnosed with hypertension) and lifestyle factors such as excessive alcohol consumption, constant tobacco (cigarette) smoking, low physical activity, having a salt-rich diet and genes (family history of hypertension). Unrestrained and prolonged hypertension increases mortality and morbidity.*

Blood pressure can be calculated by multiplying cardiac output (the amount of blood being pumped by each ventricle per minute) to total peripheral resistance (amount of resistance to blood flow).

Cardiac output is the product of heart rate and stroke volume. When both heart rate and stroke volume increase, cardiac output also increases. An increase in cardiac output would require increase in blood flow to compensate for the loss of oxygen. As a result, the heart will pump more blood thereby increasing the pressure. When resistance to blood flow increases due to increased arteriolar vasoconstriction, peripheral resistance also increases. This factor influences the blood pressure the most because of the narrowing of the arteries. This will give less space for the blood flow therefore increasing blood

pressure.*
High blood pressure affects the blood flow to the organs. It can cause narrowing of the inner lining of the arteries interrupting the flow of blood to the heart and brain, weakening of the heart muscle, aneurysm and damage to the brain such as mild-cognitive impairment, stroke and dementia.* When blood pressure is elevated, the left ventricle works harder to pump blood. This causes the thickening of the myocardium in the left ventricle which enlarges the heart. Since increased coronary blood flow support is required, failure to maintain adequate amount will eventually lead to death of parts of the heart muscle and replacement of fibrous tissue.*

Increased blood pressure caused by increased peripheral resistance will also interrupt the smooth flow of blood to the kidneys which can cause kidney failure and scarring of the glomeruli. This gives rise to the renin-angiotensin-aldosterone system. The decreased blood flow to the kidneys will cause the kidneys to release renin which allows the conversion of angiotensinogen (inactive protein produced in the liver) to angiotensin I. Angiotensin I will be converted by the angiotensin converting enzyme (ACE) to angiotensin II which is the most dominant vasoconstrictor in the body. Vasoconstriction will increase peripheral resistance. When kidneys release renin, it also causes release of aldosterone. Aldosterone increases sodium ion and water reabsorption and so increasing the volume of the blood. When the heart begins to contract, it will then send more blood causing the cardiac output to increase. Increased cardiac output and peripheral resistance would mean an increase in blood pressure.*