Memory Loss Following Heart Surgery

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More than 500,000 Americans undergo coronary artery bypass surgery each year for the treatment of angina and vascular insufficiency. People who've undergone bypass surgery for heart disease often have trouble concentrating and remembering. The exact cause of these cognitive problems is not clear, but there are probably many factors. They include the impact of anesthesia and major surgery, disruption of oxygen flow to the brain during the procedure, damage to blood vessels, and a generalized inflammatory response with increased permeability of the blood-brain barrier (a physiological mechanism that modifies capillaries, preventing certain substances from entering the brain). A crucial question is whether these troubling effects are temporary or permanent. A related question is, to what extent did these deficits exist prior to surgery?

In a report published in the New England Journal of Medicine in 2001, researchers at Duke University reported that 53 percent of coronary artery bypass surgery patients had cognitive deficits upon to be more severe. You have hypertension if your systolic blood pressure (the pressure while the heart is beating) is consistently 140 mm Hg or higher or if your diastolic blood pressure (the pressure between beats) is consistently 90 mm Hg or higher.

We think that hypertension impairs memory by damaging tiny blood vessels that terminate in the brain's white matter, the bundles of axons that transmit messages throughout the brain and central nervous system. Lesions, or abnormalities, in white matter occur to some degree in virtually everyone older than age sixty and contribute to age-related memory loss. But people with hypertension have more extensive white matter damage than same-age peers with normal blood pressure.

Research suggests that hypertension that is inadequately treated might also predispose you to dementia. There's an additive effect;

discharge from the hospital. Although the incidence of cognitive problems declined to 24 percent after six months, the authors surprisingly found an increase in problems at a five-year follow-up, with 42 percent of cases exhibiting deficits. In contrast, a German research group included a strong postoperative management approach to control vascular risk factors and found overall neuropsychological improvement in their fifty-two patients at a follow-up in thirty-two to sixty-five months; no patient exhibited global cognitive decline.

Newer surgical methods, including an "off-pump" approach, appear to offer better cognitive outcomes. Long-term cognitive outcomes after bypass surgery will improve with future investigation of the use of neuroprotective agents before surgery, ongoing refinement of anesthesiologic and surgical techniques, and a strong commitment to management of vascular risk factors in the postsurgical phase.

brain imaging studies suggest that increased blood pressure can cause small strokes, which can then cause dementia. Hypertension also increases the risk for heart disease, which can cause memory loss. One common treatment for heart disease, coronary artery bypass surgery, can itself lead to memory impairment. (See the sidebar "Memory Loss Following Heart Surgery.")

The good news is that we think that lowering blood pressure may help preserve memory and other brain functions well into old age. So if you have hypertension, see your doctor and make sure it's adequately treated.

Diabetes. High blood sugar, the hallmark of diabetes, can impair the function of the hippocampus, the brain structure that consolidates declarative memories (for names, faces, dates, and other fac-

tual information). It's easy to understand why this happens. When sugar is elevated in the blood, it's not high enough in other parts of the body, including the brain. So the brain is low on fuel. Research has also demonstrated that diabetes can cause structural damage to the hippocampus and medial temporal lobes of the brain.

Memory problems are common among people with diabetes, as well as among people with mildly impaired glucose metabolism, whose blood sugar is slightly high. In 2003, researchers at New York University School of Medicine reported that people with suboptimal glucose metabolism achieved lower scores on short-term memory tests than people with normal blood sugar. What's more, the hippocampus was smaller in people with elevated blood sugar. Suboptimal glucose metabolism (also known as reduced glucose tolerance) is one of the five characteristics of Syndrome X, a collection of risk factors for heart disease that tend to aggregate in some people. The other factors are hypertension, elevated triglyceride, low HDL (good cholesterol), and abdominal obesity.

Evidence also suggests that people with diabetes mellitus (type 1 diabetes) may be at increased risk of developing Alzheimer's disease later in life. Again, the connection between diabetes and the risk of developing a memory disorder is almost certainly due to the link between diabetes and cerebrovascular disease. Although insulin injections, needed by many people who have type 1 diabetes, can cause mild memory impairment, this effect is typically seen only immediately after the medication is administered and usually resolves completely. So if you have either type 1 or type 2 diabetes, it's vital to get appropriate treatment not only to get your blood sugar under control but also to guard against possible further memory decline.

If your blood sugar is normal, take measures to keep it that way. Type 2 diabetes is primarily a disease of poor health habits: being sedentary and overweight. By maintaining normal weight and exercising regularly, you can prevent this disease and help keep your cognitive function in good shape. (For more informa-64, tion, see Chapter 9.)

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