Factors predicting walking intolerance in patients with peripheral arterial disease and intermittent claudication

Objective. To determine which physiological variables conduce to walking intolerance in patients with peripheral arterial disease (PAD). Design. The physiological response to a graded treadmill exercise test (GTT) in patients with PAD was characterised. Setting. Patients were recruited from the Department of Vascular Surgery, Groote Schuur Hospital, Cape Town. Subjects. Thirty-one patients diagnosed with PAD were included in the study. Outcome measures. During a GTT, peak oxygen consumption (VO(2peak)), peak minute ventilation (VE(peak)), peak heart rate and peak venous lactate concentrations were measured and compared with those from a comparison group. Ankle-brachial index (ABI) was measured at rest and after exercise. During the GTT, maximum walking distance (MWD) and pain-free walking distance (PFWD) were measured to determine walking tolerance. Results. Peak venous lactate concentrations did not correlate significantly with either PFWD (r=-0.08; p=0.3) or MWD (r=-0.03; p=0.4). Resting ABI did not correlate with either MWD (r=0.09; p=0.64) or PFWD (r=-0.19; p=0.29). Subjects terminated exercise at significantly (p < 0.05) lower levels of cardiorespiratory effort and venous lactate concentrations than did a sedentary but otherwise healthy comparison group: peak heart rate 156 11 v. 114 22 beats per minute (BPM); p=0.001; and peak venous lactate concentration 9.7 +/- 2.7 mmol/l v. 3.28 +/- 1.39 mmol/l; p=0.001. Conclusion. Perceived discomfort in these patients is not caused by elevated blood lactate concentrations, a low ABI or limiting cardiorespiratory effort but by other factors not measured in this study.