People with kidney disease are more likely to have heart disease than are people without kidney disease. Heart disease is more common in people with even mild to moderate kidney disease than in those of the same age and sex without kidney disease. The cause of death in people with kidney failure is most often heart disease.
On the other hand, kidney defects are common among people with heart failure and are associated with an increased risk of death. This association is observed in people of all ages. One recent study of heart failure patients reported that the majority of patients had some degree of abnormal kidney function, and that patients who did had an approximately 50 percent increased risk of death compared with patients with normal kidney function.
Another recent study identified eight separate risk factors for death among women with heart failure. Of these, abnormal kidney function was the most common, and it was associated with the greatest increased risk of death. The authors of the study concluded that abnormal kidney function, even when mild, was a major predictor of death among women with heart failure.
Common Risk Factors for Heart Disease and Kidney Disease
High blood pressure is well known to be a major risk factor for heart disease. It's also a risk factor for kidney disease. High blood pressure causes damage to small blood vessels in the kidney and is a frequent cause of kidney damage and chronic kidney disease. Damage to the kidneys activates hormone pathways that result in increased fluid overload, which compounds high blood pressure and kidney damage.
Doctors perform a serum creatinine test on most patients with heart failure. The results of this test, which measures the amount of a chemical molecule called creatinine in the blood, tell doctors how well the patient's kidneys are functioning. If the levels are rising, it's a telltale sign that the kidneys are failing. Increased serum creatinine level is also a risk factor for heart disease.
Like the story about the chicken and the egg, it's sometimes hard to tell what came first when examining symptoms of kidney disease and heart disease. Both diseases have symptoms that can contribute to an increased risk of the other. For example, high blood pressure is a symptom of kidney disease -- and it's also a risk factor for heart disease. The same is true for abnormal blood levels of certain molecules, including electrolytes (like sodium) and fats (such as cholesterol and triglycerides).
On the other hand, severe high blood pressure, excess sodium and water in the blood (fluid overload) and a reduction in heart function are symptoms of heart failure that are also risk factors for kidney disease. We'll learn more about fluid overload on the next page.
Fluid overload is most frequently caused by heart failure. As the heart weakens, blood flow returning to the heart slows, backs up in the veins and causes fluid buildup in the tissues. Heart failure also affects the kidneys, resulting in less efficient elimination of sodium and water. The retained water increases the fluid congestion.
Fluid overload can also occur as a result of kidney disease. In addition to eliminating the body's waste products, the kidneys play a role in maintaining a normal balance between sodium and fluid. The balance is no longer maintained when the kidneys are impaired, and sodium and water begin to accumulate, causing fluid overload.
When patients have some, but not too much, excess fluid in their blood, the situation can sometimes be remedied by limiting the amount of salt in their diet. Oral medicines (diuretics, or "water pills") may also be prescribed to reduce the fluid overload. However, when there's too much excess fluid, these measures stop working and eventually many people with fluid overload require hospitalization.
In the hospital, doctors may prescribe intravenous medicines like loop diuretics, vasodilator drugs (which cause blood vessels to widen so more blood can flow through) and inotropic drugs (which stimulate the heart to beat more strongly). These types of intravenous drug therapies generally require a hospital stay of around six days.
When diuretics fail to relieve the excess fluid, a procedure known as ultrafiltration may be used. On average, ultrafiltration therapy requires a hospital stay of around three to four days.
To learn more about heart and kidney disease, take a look at the links on the next page.
Related HowStuffWorks Articles
- How Your Heart Works
- How Your Lungs Work
- How Your Kidneys Work
- How Blood Works
- How Ultrafiltration Works
- How Vasodilator Drugs Work
- How Fluid Overload and Edema Work
- How Orthopnea Works
- How Jugular Venous Distension Works
- How Heart Failure Affects Quality of Life
- How Inotropic Drugs Work
- How Diuretics Work
- How Low-Sodium Diets Work
More Great Links
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