Assessing muscle vasodilation using near-infrared spectroscopy in cardiac patients

Background In patients with chronic heart failure, an inadequate increase in muscle blood flow resulting from impaired vasodilation plays a key role in their exercise intolerance. However, no non-invasive methods to assess muscle vasodilation during dynamic exercise were available. We investigated whether the changes in tissue hemoglobin and myoglobin content (total-Hb+Mb) determined by non-invasive measurement using near-infrared spectroscopy (NIRS) reflect vessel conductance of working muscle during exercise. Methods and Results Sixteen patients (10 patients with normal cardiac systolic function, 6 with cardiac dysfunction) performed incremental bicycle exercise testing. Total-Hb+Mb from the right vastus lateralis muscle was monitored using NIRS. Leg blood flow (LBF) in the right femoral vein was measured using a thermodilution technique every 30-60 s. Leg vessel conductance was calculated as LBF/mean arterial pressure at each time of the measurement. In all cases except 1, the levels of total-Hb+Mb showed significant correlation with the leg vessel conductance (r=0.792 to 0.980). Intra-subject reproducibility of the NIRS measurement was also confirmed in 6 patients. Conclusions Total-Hb+Mb from NIRS reflected muscle vasodilation during sub-maximal dynamic exercise in patients with and without cardiac dysfunction, indicating that NIRS provides a valuable method to assess the working muscle vasodilation.