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.