Abstract
It has often been reported that the impaired walking performance in people with peripheral arterial disease (PAD) is not correlated to the leg blood flow, despite the importance of blood flow to exercise performance. In contrast, some aspects of muscle oxidative metabolism have been related to walking performance in PAD. The purpose of this study was to further explore these relationships in PAD with a particular focus on skeletal muscle mitochondrial function. In 15 PAD patients (age=64.6± 8.5 y; weight=76.7± 16.3 kg), walking performance was tested on the treadmill using an incremental walking test, leg blood flow was tested at rest and after maximal calf exercise using venous occlusion plethysmography, and the mitochondrial ATP production rate (MAPR) using pyruvate, palmitoyl-carnitine, alpha-ketoglutarate and malate (PPKM) as substrates was measured on biopsy samples taken from the medial gastrocnemius muscle in the leg with the lowest ankle-brachial index (i.e.worst leg). The data are expressed as mean±standard deviation. Semi-partial correlation analysis was used to assess the unique contribution of independent variables to the variation in walking performance. The pain-free walking time (3.12± 2.59 min) was positively correlated (P less than 0.05) with MAPR when expressed per mmol ATP/min/g protein (0.3902± 0.2145, r=0.583) and per mmol ATP/min/kg muscle (4.7703± 2.3081, r=0.519), negatively correlated with body weight (r= -0.493), but not correlated with calf blood flows. However, the pain-free walking time divided by body weight was positively correlated with resting calf blood flow in the best (3.607± 1.83 ml/100ml tissue/min; r=0.577) and worst leg (3.261± 1.103 ml/100ml tissue/min; r=0.613). The total walking time was not correlated with any of these variables. MAPR and body weight accounted for 29 % and 6 % of the variation in the pain-free walking time respectively. The resting blood flow in the worst leg accounted for 7 % of the variation in the pain-free walking time divided by the body weight. Therefore, of the variables measured, skeletal muscle mitochondrial function is the most important contributor to the difference in walking performance in people with PAD. This study was funded by the QUT and University of Queensland.