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Near-infrared spectroscopy （NIRS） has been widely used to investigate muscle oxygenation at rest and during exercise. Oxygenated hemoglobin concentration（HbO2）measured by NIRS reflects oxygen supply under the condition in which oxygen consumption is assumed to be constant. A decrease in HbO2 occurs in non-exercised muscle during enhancement of muscle sy mpathetic nerve activity（MSNA). On the other hand, sympathetically mediated decrease in HbO2 is suppressed in exercising muscle due to a decreased level of muscle oxygenation by muscle activity, suggesting the occurrence of functional sympatholysis. Thus, a decrease in HbO2 in non-exercised muscle can be used as an index of enhancement of MSNA. Although microneurography is a gold-standard tool to measure MSNA, there are some limitations such as the necessity for practice, vulnerability of a motion artifact and difficulty in measurements in paralyzed regions of individuals with disabilities. However, there are no such limitations in NIRS measurements. Thus, NIRS enables estimation of the behavior of MSNA under the condition in which there is much movement of the body such as in severe exercise and enables estimation of the behavior of MSNA in a paralyzed limb of an individual with spinal cord injury. Since recent advances in technology have allowed us to use lowcost and portable NIRS devices, it is expected that NIRS devices will be used as tools to detect abnormal enhancement of MSNA such as autonomic dysreflexia in individuals with spinal cord injury. |
