By making your blood vessel walls more susceptible to atherosclerosis, hypertension increases not only your likelihood of having a stroke, but also your risk of heart attack. When coronary arteries become completely blocked by debris such as fats, cholesterol, and dead cells or a clump of platelets, a heart attack results. Fragments from these deposits in the aorta, called emboli, can also break away, travel through the bloodstream, and eventually block other vessels, such as those supplying the legs (causing circulatory problems) or the brain (causing stroke).
Having high cholesterol in addition to hypertension only exacerbates this process and increases your risk of cardiovascular complications.
In addition to making atherosclerosis more likely, hypertension also forces the heart to work increasingly harder to drive blood through the body. As a result, the left ventricle, the heart’s main pumping chamber, becomes thicker and more muscular in order to contract with greater force. This compensation — known as left ventricular hypertrophy (LVH) — eventually becomes counterproductive. As the heart muscle enlarges, it needs progressively more oxygen, but the arteries, which are also thickened and narrowed as a result of hypertension, become less able to deliver it. The lack of oxygen can cause angina (chest pain) and, if severe enough, a heart attack.
The combination of LVH and diseased coronary arteries — spurred on by hypertension — may also lead to congestive heart failure (the inability of your heart to pump blood efficiently throughout your body). In fact, if you have uncontrolled high blood pressure, you’re twice as likely to develop heart failure as someone without hypertension.
Unlike your biceps, the thickness of your heart muscle doesn’t translate into strength. With LVH, your heart muscle thickens, but your blood supply usually can’t swell to the same degree, especially if your arteries are damaged. Without an adequate supply of blood, your heart weakens, and this in turn can lead to either of the two primary kinds of congestive heart failure — systolic or diastolic. Systolic heart failure arises when your heart cannot pump forcefully enough to push a sufficient amount of blood into circulation. Diastolic heart failure occurs when your heart can’t properly fill with blood because it’s stiff and has trouble relaxing.
Symptoms of heart failure include weakness and fatigue (because your muscles aren’t getting enough blood), shortness of breath, and the accumulation of fluid in your lungs, feet, ankles, and legs (known as edema).
By encouraging atherosclerosis, hypertension can contribute to dementia. Atherosclerosis interferes with circulation, and a lack of blood supply can produce areas of dead tissue in the brain called small infarcts. Multi-infarct dementia, a well-recognized cause of memory loss in older people, is caused by a series of these tiny strokes. Each one affects such a small area of the brain that symptoms may not be apparent until a substantial amount of tissue has been destroyed.
The link between multi-infarct dementia and hypertension escaped attention for many years because people suffering from dementia often have normal or low blood pressure. But long-term studies now show that blood pressure in midlife may predict brain function years later.
The kidneys play a critical role in the body’s natural control of blood pressure by regulating the amount of water and sodium in circulation. When blood pressure rises, the kidneys excrete water and sodium. This action helps bring pressure back down by stimulating the loss of body fluids (through urination, for example), thereby reducing the volume of circulating blood. When blood pressure falls, the kidneys retain water and sodium to conserve blood volume and raise pressure.
Sustained high blood pressure damages the structures in the kidneys, called glomeruli, which filter waste products, sodium, and water from the bloodstream. Glomerular destruction due to hypertension is one of the most common causes of renal failure (loss of kidney function). People with renal failure become bloated with excessive fluid and weakened by the accumulation of toxic chemicals normally excreted by the kidneys. Uncontrolled hypertension is second only to diabetes as a cause of renal failure, accounting for about 26% of new cases.
The eye works by focusing visual images onto the retina, a sheet of nerve tissue at the back of the eyeball. Immediately behind the retina lies a network of tiny blood vessels that keeps this tissue richly supplied with oxygen and nutrients. Hypertension can cause these arteries to narrow or break and bleed into the retina. It can also lead to swelling of the optic nerve, which carries images to the brain. In patients with longstanding, untreated hypertension, the result can be impaired vision and even blindness.