Extending the Range of Treadmill Testing for Patients with Intermittent Claudication

Abstract

There is a need to evaluate patients with peripheral arterial disease (PAD) with a limited or extended walking distance. We aimed to enable an estimation of walking distance as measured on a frequently used "standard" graded (3.2 km·h(-1), 2% increase per 2 min) protocol for walking distances measured on protocols with a lower or higher workload. Patients with PAD and an absolute claudication distance (ACD) of <500 or between 1000 and 1600 m as measured with the "standard" protocol were included. Four graded study treadmill protocols, two with lower and two with higher workload than the "standard" protocol, were developed. Two study protocols (low or high) and the "standard" protocol were repeated in random order. Quality was determined with the intraclass correlation coefficient and the coefficient of variation. Orthogonal regression analysis was used to predict walking distances on the standard protocol on the basis of the study protocols. Forty-three patients with an ACD <500 m and 23 patients with an ACD between 1000 and 1600 m were included. Because feasibility from the protocols with 2.0 km·h(-1) and 2% increase every 2 min and 4.4 km·h(-1) and 2% increase every minute was highest, they were calibrated against the "standard" protocol, and reliability was comparable with the "standard" protocol. The coefficient of variation between the prediction of walking distance on the "standard" protocol on the basis of the new protocols and the measured distances were in the same range (22%-25%) as the variation measured performing the same treadmill test twice. An accurate estimate of walking distance as measured on a "standard" treadmill protocol can be derived from a protocol with a lower or higher workload.