Lower-extremity peripheral arterial disease (PAD) is a chronic progressive atherosclerotic process that diminishes blood flow to the musculature, leading to a mismatch of oxygen delivery and metabolic demand during physical activity (5). PAD affects approximately 8 to 10 million men and women in the United States, which represents an age-adjusted prevalence of 12% of the population (4,9). Clinically, PAD is often manifested as intermittent claudication, which is often described as a cramping, aching, burning, or pain located in the calves, buttocks, or thighs noted during physical activity and resolving only with rest (5). These symptoms are present in 15% to 50% of those with PAD, resulting in an impaired quality of life and limited activity levels (9,10,16,21).
IMPACT OF PAD ON PHYSICAL ACTIVITY AND LIFESTYLE
Patients with PAD can demonstrate significant functional impairment from claudication, resulting in a rapid functional decline (13,14). This functional decline translates into a 45% reduction in daily physical activity, resulting in a significantly deconditioned state that often causes individuals to become housebound or dependent upon others (5,7). These limitations often result in feelings of social isolation, a sense of inadequacy, and a perception of being a burden on friends and family (27). In addition, the reduced physical activity may lead to an aggravation of other coexisting medical conditions, further increasing the risk of cardiovascular disease morbidity and mortality (5).
USE OF EXERCISE REHABILITATION AS A TREATMENT FOR PAD
In 2001, the American Heart Association (AHA) and American College of Cardiology (ACC) released a consensus statement that emphasized the importance of aggressive risk-reduction therapies for patients with coronary and other atherosclerotic vascular disease, including PAD (22). The conclusion of the consensus statement used growing evidence that supported the use of aggressive comprehensive risk factor management to improve survival, reduce recurrent events, and improve quality of life for these patients (22). These guidelines were updated in 2006 to include additional important evidence that further supported or enhanced the previous recommendations (23).
As part of the AHA/ACC recommendations, exercise therapy was found to be safe and clinically effective at decreasing the symptoms associated with intermittent claudication. Benefits include a reduction in claudication symptoms as well as increases in walking speed, distance, and duration (5,6,11). In addition, improvements in routine daily activities have been associated with exercise rehabilitation (17). Most data support the use of exercise rehabilitation performed in a supervised hospital-based rehabilitation setting as the most effective means of improving exercise performance when compared with unsupervised exercise sessions (16,18,24). Recent data, however, suggest that patients with PAD, both with and without claudication, who perform a self-directed walking program, can achieve significant benefits as well (15).
Despite the recognition that exercise therapy improves claudication, the mechanism by which this occurs is less clear. There seems to be a combination of physiological, metabolic, and mechanical alterations that occur during exercise that stimulate an adaptive response to ultimately reduce the claudication symptoms (24). Several mechanisms have been identified that play a role in the overall improvement of claudication; however, the degree to which each is involved has yet to be determined. These mechanisms include enhanced oxygen extraction and metabolism (7), improved vascular endothelial function (3), improved walking economy (28), an attenuated inflammatory response (26), potential development of collateral circulation (7), and redistribution of blood flow from inactive to active muscles (25). Regardless of the mechanism, exercise training has been shown to be an effective low-cost therapy to improve the functional ability of patients with intermittent claudication.
EXERCISE PRESCRIPTION FOR THE PAD PATIENT
Because patients with intermittent claudication often have concomitant coronary artery disease, hypertension, or diabetes, adverse responses during exercise training are possible (24). Thus, it is recommended that a treadmill exercise test be performed before the initiation of an exercise program to avoid adverse outcomes that may be precipitated by physical activity (1).
Walking has been found to be the most effective exercise for claudication, with the initial treadmill speed set at a level to initiate claudication pain within 3 to 5 minutes (24). Walking should occur at this workload until claudication of moderate severity occurs, followed by resting in a seated or standing position until the claudication is resolved. This intermittent exercise pattern should be repeated until a minimum of 35 minutes of walking time is accumulated per exercise session. Once the ability to obtain 35 total minutes of exercise in a given session has occurred, progression of the exercise program should include a goal to increase walking time by 5 minutes per session until a total walking time of 50 minutes is achieved (24). Progression of exercise also should occur if walking time exceeds 10 minutes before the onset of claudication (5). Initial changes in intensity should come from increasing walking speed if less than 2 mph, however, for those walking at speeds greater than 2 mph, an increase in walking grade also can be used (5). Walking should occur 3 to 5 times per week, with an additional goal to increase physical activity performed throughout the day.
Aside from a reduction in functional capacity, many patients with claudication experience a loss of muscle mass, strength, and endurance, further exacerbating their physical impairment (20). Although resistance training has traditionally been recommended for use as a rehabilitative exercise for other cardiovascular diseases, the use of resistance training has shown less benefit on intermittent claudication symptoms when compared with treadmill exercise training (8). In addition, the combination of resistance training exercise and treadmill exercise does not provide additional benefit to walking ability beyond treadmill walking alone (8,17).
Because PAD has similar risk factors as other cardiovascular diseases, an increase in the availability of supervised rehabilitation programs is necessary to provide the most optimal postdiagnosis care. In fact, because of the growing recognition of the adverse effect of claudication on functional capacity and quality of life and the positive effect that exercise training can have on claudication, a Current Procedural Terminology code (93668) has been available since 2001 for exercise rehabilitation (5). Unfortunately, participation by those with PAD is often limited by significant barriers (5,19) (see Table), resulting in a utilization rate that is less than half of those affected by the disease (2). It should be the goal of the exercise professional, particularly those involved in cardiac rehabilitation programs, to raise awareness among physicians and the lay population regarding the benefits of rehabilitation in those with claudication.
Similar to those who have claudication, asymptomatic patients with PAD also are at a high risk for functional decline. Although the data are somewhat limited, self-directed walking programs have shown an ability to reduce the functional decline in patients with PAD, regardless of symptoms (15). As claudication is present in only 15% to 50% of those with PAD (10,21), significant benefits could be achieved by screening for and identifying those asymptomatic individuals who have PAD and who may benefit from walking exercise (15). The identification of PAD at its earliest stage and encouragement to participate in a walking program, whether claudication is present or not, could lead to improved functional and cardiovascular outcomes, enhanced patient compliance, and lowered health care costs (12,15). Many cardiac rehabilitation centers have the capability to accommodate patients with PAD, providing them with an environment that is conducive to a lifestyle change that emphasizes long-term compliance with exercise and risk factor modification (24). Not only will this provide benefits to those who have the disease, but also provide an additional revenue stream to the rehabilitation center, allowing for better use of staff and resources.
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