The presence and severity of peripheral arterial disease, as measured by comparing blood pressures in the arm and leg, and the nature of the leg symptoms a patient experiences can be used to identify those at highest risk of decline in walking endurance, according to a study in the July 28 issue of JAMA, the Journal of the American Medical Association.
Peripheral arterial disease (PAD) is a chronic condition that results from narrowing of the vessels that supply oxygen-rich blood to the legs, abdomen, pelvis, arms, or neck. The most commonly affected area is the legs.
According to background information in the article, cross-sectional studies demonstrate that distinct types of leg symptoms reported by patients with PAD in the lower extremities are associated with varying degrees of functional impairment. Severity of PAD, as measured by the ankle brachial index (ABI), is also associated with the degree of functional impairment. However, relationships between ABI, leg symptoms, and functional decline are unknown.
A patient is tested for PAD by measuring blood pressure at the ankle and in the arm while the person is at rest, and then repeating both measurements after five minutes of walking on a treadmill. ABI is calculated by dividing the blood pressures measured in the lower leg by the blood pressure measured in the arm. A normal resting ABI is greater than 1.00 or 1.10, and a decrease in ABI with exercise or a resting ABI of < 0.90 are sensitive indicators that significant PAD is probably present.
Mary McGrae McDermott, M.D., of Northwestern University Feinberg School of Medicine, Chicago, and colleagues conducted a prospective cohort study among 417 people with PAD and 259 without PAD. The participants were age 55 and older, and had baseline functional assessments between October 1, 1998, and January 31, 2000, with follow-up assessments scheduled one and two years afterward. PAD was defined as ABI less than 0.90, and participants with PAD were categorized at baseline into one of five mutually exclusive symptom groups.
The researchers measured annual changes in six-minute walk performance and in usual-paced and fast-paced four-meter walking velocity, adjusted for age, sex, race, prior-year functioning, coexisting diseases, body mass index, cigarette smoking, and patterns of missing data.
"Among 676 men and women age 55 years and older, participants with low ABI levels at baseline had significantly greater decline in walking endurance at two-year follow-up, compared with those with normal baseline ABI levels," the authors write. "Participants with ABIs less than 0.50 at baseline had a nearly 13-fold increased risk of becoming unable to walk for six minutes continuously two years later, relative to participants with ABIs of 1.10 to 1.50."
Baseline leg symptoms among participants with PAD also predicted rates of functional decline. "Participants with PAD having leg pain on exertion and rest experienced greater declines in walking endurance and walking speed than did individuals without PAD," the authors write. "Participants with asymptomatic PAD had significantly greater declines in six-minute walk performance than did participants without PAD."
"Previously reported lack of worsening in claudication symptoms over time in patients with PAD may be more related to declining functional performance than to lack of disease progression," they suggest. Claudication is pain in the legs that is typically felt while walking, and subsides with rest.
"Our findings underscore the importance of using the ABI to identify persons with PAD, since PAD is frequently undiagnosed or asymptomatic," the authors conclude. "Further study is necessary to develop treatments to prevent functional decline in patients with PAD who do not have classic intermittent claudication."