Improving Functional Outcomes in Patients with Intermittent Claudication

Assessing Function Outcomes

Functional capacity is a multidimensional construct that represents the highest level of activity that a person may reach at a given moment in a standardized environment [10]. It can encompass one’s ability to perform work-related activities (eg, lifting, static work), activities of daily living (eg, walking, climbing stairs, standing up from a chair), and other exercise-related activities (eg, walking, cycling, weight lifting). Given that the primary functional limitation in intermittent claudication is walking impairment, most functional capacity evaluations in this population focus on walking capacity as the outcome of interest. In terms of walking impairment, individuals with intermittent claudication have poorer walking endurance and slower walking velocity compared to individuals without PAD [4]. People with intermittent claudication may reduce their walking activity to avoid leg symptoms. Thus, clinicians should not equate stabilization or improvement in intermittent claudication with stabilization or improvement in walking performance [11].

There are several methods for assessing walking capacity in individuals with intermittent claudication. Treadmill walking tests are commonly used. Following a transatlantic conference on clinical trials guidelines in PAD [12], two internationally accepted treadmill protocols were recommended: (1) constant-pace treadmill protocol (constant walking speed of 3.2 km·h ^–1 at 10%–12% gradient), and (2) incremental treadmill protocol (starting horizontally at a constant speed of 3.2 km·h ^–1, but with the gradient increasing in pre-defined steps (eg, 2%) at pre-defined time intervals (eg, every 2 minutes). The main variables measured during treadmill testing are (1) time to the onset of claudication pain (ie, claudication onset time), and (2) peak walking time, at which point patients request to stop, usually because of intolerable claudication pain [13]. The latter measure is used most frequently in clinical trials as the primary outcome. Previous terms for these variables include pain-free walking distance/time and maximum walking distance/time, respectively.

The 6-minute walk test is an alternative to treadmill testing that is highly reproducible, valid, and sensitive to change in patients with claudication [14,15]. Advantages of this test include the lack of need for special equipment and that it provides a better approximation of community walking compared to treadmill walking in older patients [16,17]. More recently, global positioning system technology has been used to provide an objective assessment of walking capacity under free-living conditions in patients with intermittent claudication [17,18]. This may provide a useful method for physicians who do not have a treadmill and have trouble performing a 6-minute walk test (eg, due to space limitations); however, the validity and reliability of this method is dependent on patients adhering to standardized instructions for conducting a self-managed walking assessment in the community.

Self-reported walking capacity, assessed using standardized questionnaires, can provide a convenient alternative to objective measurement procedures. Various questionnaires have been proposed, of which the Walking Impairment Questionnaire (WIQ) is the most widely used. The WIQ, which was proposed over 20 years ago to standardize the estimation of walking limitation by patient interview [19], involves 14 items with 5 possible items for each item. The 14 items are divided into 3 sub-scales: a distance sub-scale (7 items), a speed sub-scale (4 items), and a stair-climbing sub-scale (3 items). It has been translated into several languages [20–22] and has been shown to be responsive to various treatment modalities [23,24]. Recently, a new shorter questionnaire has been proposed for estimating walking capacity in intermittent claudication, the Walking Estimated Limitation Calculated by History (WELCH) questionnaire [25,26]. Patients are required to report the maximum duration (8 possible responses ranging from “impossible” to “3 hours or more”) they can walk at 3 different speeds (ranging “slow” to “fast”), as well as what their normal walking speed is in comparison to their friends, relatives, and people of a similar age. Compared to the WIQ, the WELCH is shorter, suffers fewer errors when self-completed, provides comparable correlation with treadmill walking capacity data, and can be easily scored without a calculator or computer spreadsheet [25,27,28]. Further research is needed to assess its responsiveness to various interventions. Many other generic and disease-specific questionnaires have been proposed for assessing functional status and quality of life in claudication patients; an extensive review of these questionnaires can be found elsewhere [29]. In our opinion, very few questionnaires besides the WIQ and WELCH are useful for the routine assessment of patients’ walking limitation.