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CHICAGO, Aug. 2 -- High blood pressure appears to impair older individuals' ability to walk, and the reason may be more than just peripheral arterial disease.

A study of elderly clergy, both men and women, found a significantly accelerated decline in leg function in those with higher blood pressures-about 30% more loss per year at a systolic pressure of 160 mm Hg compared with 120 mm Hg.

Studies have previously shown that peripheral arterial disease, such as leg claudication, affects walking ability, but little has been known about causes of gait difficulty or why some patients develop more trouble walking than others as they age.

"What we're pointing to is that blood pressure might work through other mechanisms rather than just peripheral arterial disease to cause that walking difficulty," said Raj C. Shah, M.D., of the Rush Alzheimer's Disease Center here, reporting in the August issue of the Journal of Gerontology: Medical Sciences. "It might be due to small strokes."

Dr. Shah and colleagues followed 888 participants in the Religious Orders Study over an average of 7.8 years.

Annual evaluation included gait speed, ability to rise from a chair, and balance skills, all of which have been shown in other studies to impact ability to perform instrumental activities of daily living and predict of the risk of nursing home admission and death.

Participants in the current study were evaluated for cognitive function, vascular disease, diabetes, and blood pressure at baseline. Those with dementia or Parkinson's disease were excluded. The average systolic and diastolic blood pressures were 135 mm Hg and 75 mm Hg, respectively. The mean age was 75 years and 69% of the participants were women.

Elevated systolic pressure had the most consistent effect on lower limb function decline. Systolic pressures above 160 mm Hg (P=0.016) were associated with decline in lower limb function. Each 10 mm Hg increase in systolic blood pressure was associated with a significant increase in the rate at which leg function declined (P=0.011). However, systolic pressure did not predict the level of limb function itself.

A diastolic blood pressure greater than 90 mm Hg (P=0.023) (rather than continuous measures) were also associated with a decline in gait over time.

Interestingly, although the inclusion of individuals who had a previous stroke did not diminish the association between leg function and blood pressure, controlling for strokes that occurred during the study eliminated the significance of the association (P=0.099).

Since higher blood pressure is known to contribute to the risk for stroke, Dr. Shah postulated that clinical stroke may be the mechanism by which blood pressure reduces walking ability.

"Some of the strokes can be very minimal so the patients won't even recognize that they even have a stroke," he said, "but they might notice that their walking has changed or they've slowed down a bit."

Since hypertension does not cause pain or headaches for the most part that would draw patients' attention, decline in walking ability may be another reason for physicians to work to tighten blood pressure control.

"For now this will require further study to see if lowering blood pressure actually stops the decline in walking ability," Dr. Shah said.

Although almost half of the patients were taking antihypertensive medication at baseline, just taking the medications alone did not have an effect on the association between gait decline and blood pressure.

"It's not that you're on an agent that affects things or might change things," Dr. Shah said. "It's more that your blood pressure is under control that might make a bigger difference."

Controlling for baseline factors including cognitive function, diabetes, previous myocardial infarction, and leg claudication did not affect the association between systolic blood pressure and walking ability.

The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure's seventh blood pressure guidelines report (JNC VII) defines normal blood pressure as systolic of less than 120 and diastolic less than 80 mm Hg. It defines stage 1 hypertension as 140 to 159 mm Hg systolic and 90 to 99 mm Hg diastolic and stage 2 hypertension as a systolic of 160 mm Hg or greater and diastolic of 100 mm Hg or greater.

The American Heart Association recommends a healthy lifestyle, including a nutrient-dense diet rich in vegetables and fruits along with physical exercise, for older adults to reduce cardiovascular risk and lower blood pressure.

High blood pressure is a risk factor that can be controlled to help people stay active and independent as they age, Dr. Shah noted.

This study was funded by the National Institute on Aging.

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