The Effects Of Incremental Treadmill Walking On Skeletal Muscle Oxygenation In Older Cardiovascular Rehabilitation Participants

Abstract

Pulse oximetry is commonly used to monitor arterial oxygen saturation (SpO2) during exercise in individuals with cardiovascular disease. However, many of these individuals often exhibit poor exercise tolerance despite normal SpO2 values. We propose that near-infrared spectroscopy (NIRS), a non-invasive method of estimating skeletal muscle oxygen saturation (StO2), may be more suitable for monitoring acute exercise responses in select patient populations. PURPOSE To examine the effects of incremental treadmill walking on SpO2, StO2, and calf blood flow (BF) in healthy elderly individuals (CON; n=20; 58±6 yr), individuals with coronary artery disease (CAD; n=14; 67±7 yr), and individuals with peripheral artery disease (PAD; n=5; 68±6 yr). METHODS SpO2 and StO2 were assessed before, during, and after an incremental treadmill test. The treadmill protocol consisted of seven possible stages with a constant speed of 2.0 mph and 3.5% increases in grade for each three-minute stage. Calf BF was assessed with venous occlusion plethysmography before and five minutes after the treadmill test. ANOVA with repeated measures were used to analyze the data. RESULTS There were no significant group differences at rest for StO2 (CON: 73±15%; CAD: 71±16%; PAD: 68±21%), SpO2 (CON: 97±1%; CAD: 97±1%; PAD: 97±2%), or BF (CON: 1.7±0.7; CAD: 1.3±0.5; PAD: 1.3±0.5; units = ml blood 100 ml tissue−1 min−1). Treadmill walking induced significant increases in BF for all groups (122%, 106%, and 132% for CON, CAD, and PAD, respectively; all p < 0.001), but did not significantly alter SpO2 in any group. The PAD group exhibited significantly shorter walking times than both the CON and CAD groups (14.4 vs. 20.1 and 19.1 min, respectively; p < 0.05), most likely due to StO2 values that were significantly lower than the CON and CAD groups during multiple stages of treadmill testing (each p < 0.05). CONCLUSIONS Although the three groups had similar SpO2 and BF responses to incremental treadmill walking, the PAD group had significantly lower StO2 values, indicating that skeletal muscle dysfunction is a major limiting factor on exercise capacity in these individuals. Thus, NIRS may be a more useful tool than pulse oximetry for monitoring the effects of acute and chronic exercise on those with PAD.