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/1; 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.