Signs and Symptoms
The patient with hypertension tends to be older and the prevalence of the disease increases with age. However, 2 percent of children have hypertension while another 5 percent are borderline. Black adults have a higher incidence of hypertension than Caucasian adults and typically a more severe form of the disease. Risk factors for the development of hypertension include a positive family history of hypertension or cardiovascular disease, diabetes, hypercholesterolemia, obesity, sedentary lifestyle, high sodium intake, high dietary fat intake, alcohol use, smoking, and a stressful lifestyle.
Hypertension is defined as systolic blood pressure (BP) exceeding 140mmHg and/or diastolic BP exceeding 90mmHg measured at least twice on separate days. About 90 percent of cases are due to essential hypertension, while the remaining cases are secondary to another disease, such as renal parenchymal disease or pheochromocytoma. There is also isolated systolic hypertension and isolated diastolic hypertension.
Hypertension is manifested within the eye as both hypertensive retinopathy and hypertensive ocular complications. Hypertensive ocular complications include retinal vessel occlusion, ocular ischemic syndrome, non-arteritic anterior ischemic optic neuropathy, internuclear ophthalmoplegia, cranial nerve palsy, nystagmus and midbrain syndrome, and amaurosis fugax and transient ischemic attack.
Essential hypertension develops from renal system dysfunction. The kidney is a filtering organ that retains vital blood components and excretes excess fluid. If too much fluid is retained, BP rises. If too little fluid is retained, BP decreases. Arterial pressure within the renal artery triggers a feedback loop. The kidneys excrete sodium, which osmotically draws fluid into the excretory system in a process called pressure diuresis. This causes a decrease in blood fluid volume and arterial pressure.
As pressure within the renal artery decreases, the kidneys reflexively secrete an enzyme called renin. This enzyme causes the formation of a protein called Angiotensin I. Angiotensin I directly stimulates the kidneys to retain sodium and fluid. Angiotensin I is converted in the lungs, via the enzyme angiotensin converting enzyme (ACE) to Angiotensin II. Angiotensin II is a potent vasoconstrictor which increases total peripheral vascular resistance and hence elevates BP.
As BP elevates, the whole system begins again with pressure diuresis. In healthy individuals, this feedback loop maintains a constant blood pressure with only minor fluctuations. In patients with essential hypertension, this feedback loop fails for undiscovered reasons. The result is a higher than normal level of pressure within the renal artery necessary for pressure diuresis to occur.
Hypertension plays a significant role in the development of arteriosclerosis and atherosclerosis. Hypertension reduces the elasticity of vessels allowing lipids to deposit in the form of atheromas, which in turn leads to thrombus formation and possible emboli formation. This impedes blood flow and leads to ischemic disease.
Coronary heart disease is the leading cause of death in hypertensive patients. Ventricular hypertrophy occurs as a result of increased cardiac output in the face of systemic vascular resistance. Eventually, the heart is unable to maintain this constant output and the hypertrophied muscle outstrips its oxygen supply.
Cerebrovascular disease is a serious complication of hypertension. Hypertension is the leading cause of stroke. Hypertension-mediated atherothrombotic lesions are the cause.
Hypertension-induced arteriosclerosis may also result in atrophy of the renal glomeruli and tubules. This results in a malignant form of hypertension, and renal failure is also a frequent cause of death.
Reducing morbidity and mortality is the main goal in hypertension management. Blood pressure reduction is done in a step-wise approach, often beginning with non-pharmacologic methods that include weight loss, and dietary and lifestyle modifications.
Should non-pharmacological methods prove unsuccessful, there are four families of drugs from which to choose:
1. Diuretics (reduce blood volume by inhibiting sodium and water retention)
2. Beta blockers (decrease cardiac output)
3. Calcium antagonists (induce vasodilation)
4. ACE inhibitors (decrease peripheral vascular resistance)
Medications from each family may be combined in order to achieve the desired pressure reduction.
Hypertensive complications are mediated through arteriosclerosis and atherosclerosis.
Weight reduction is the most potent non-pharmacological method of hypertension management.