MUSCLE OXYGENATION BETWEEN THE PARETIC AND NONPARETIC LEG MEASURED DURING ARTERIAL OCCLUSION AND EXERCISE IN CHRONIC STROKE

Abstract

<h3>BACKGROUND</h3> Oxygen delivery and demand are reduced in the paretic leg of individuals post-stroke, reflecting decreases of vascular function and reductions of muscle quantity and quality. However, it is unknown how muscle oxygenation, the balance between delivery and utilization of oxygen, at the muscle is altered post-stroke and how it relates to functional ambulation and aerobic exercise. The purpose of this study was to determine the difference in muscle oxygenation between the paretic and nonparetic leg of post-stroke individuals and determine if there is an association with the six-minute walk test (6MWT) distance. <h3>METHODS AND RESULTS</h3> This was a single group cross-sectional study and a sub-study of a larger two-arm parallel-group superiority trial. Skeletal muscle O2 saturation (SMO2) of the paretic and nonparetic vastus lateralis muscles were monitored continuously with two near-infrared spectroscopy (NIRS) devices, a non-invasive measure of muscle oxygenation. NIRS outcomes were measured at rest, during arterial occlusion, acute submaximal exercise and 6MWT. Muscle oxygenation was evaluated by the rate of SMO2 deoxygenation and reoxygenation during and after occlusion and exercise, and by SMO2 averages for rest and the 6MWT (see figure). Eleven subjects (91% male; 32.2±6.1 months post-stroke; age 62.9±13.6 years, with a Chedoke–McMaster Stroke Assessment score of 4.1±1.4 of the paretic leg; 7 representing normal movement) participated. There was no significant difference in SMO2 between legs at rest (p=0.13) or during the 6MWT (p=0.26). The arterial occlusion desaturation slope in the nonparetic leg (-0.70±0.36%/second) was significantly steeper than the paretic leg (-0.53±0.24%/second; p=0.03), suggesting impaired oxygen consumption in the paretic leg. The post-occlusion resaturation slope was significantly steeper in the nonparetic leg (5.7±1.6%/second) compared to the paretic leg (4.6±1.8%/second; p=0.04), indicating poorer microvascular function in the paretic leg. The exercise deoxygenation slope in the paretic leg (-0.6±0.6%/second) was significantly steeper than the non-paretic leg (-0.3±0.2%/second; p=0.047), indicating a greater mismatch between oxygen delivery and consumption at the onset of exercise, however, there was no significant difference between legs in the post-exercise resaturation slope (p=0.39). Average 6MWT SMO2 of each leg was not significantly correlated with 6MWT distance (Paretic: r=-0.06, p=0.85; Nonparetic: r=0.25, p=0.46). <h3>CONCLUSION</h3> Oxygen consumption and microvascular responsiveness are reduced in the paretic compared to the nonparetic leg. At the onset of exercise there is a mismatch between oxygen delivery and consumption in the paretic leg, which may require strategies to improve muscle oxygenation in this population.