Near-infrared spectroscopy using indocyanine green dye for minimally invasive measurement of respiratory and leg muscle blood flow in patients with COPD

Reliability of Near-infrared spectroscopy (NIRS), measuring indocyanine green (ICG) for minimally invasive assessment of relative muscle blood flow during exercise has been examined in fit young individuals, but not in COPD. Here we ask whether it could be used to evaluate respiratory and locomotor muscle perfusion in COPD patients. Vastus lateralis muscle blood flow (MBF, the reference method calculated from arterial and muscle ICG concentration curves) and a blood flow index (BFI, calculated using only the (same) muscle ICG concentration curves) were compared in 10 patients (FEV1:51{plus minus}6%predicted) at rest and during cycling at 25%, 50%, 75% and 100% of WRpeak. Intercostal muscle MBF and BFI were also compared during isocapnic hyperpnea at rest, reproducing ventilation levels up to those at WRpeak. Intercostal and vastus lateralis BFI increased with increasing ventilation during hyperpnea (from 2.5{plus minus}0.3 to 4.5{plus minus}0.7nM/s) and cycling load (from 1.0{plus minus}0.2 to 12.8{plus minus}1.9nM/s), respectively. There were strong correlations between BFI and MBF for both intercostal (r=0.993 group mean data, r=0.872 individual data) and vastus lateralis (r=0.994 group mean data, r=0.895 individual data). Fold changes from rest in BFI and MBF did not differ for either the intercostal muscles or the vastus lateralis. Group mean BFI data showed strong interrelationships with respiratory and cycling workload, and whole body metabolic demand (r ranged from 0.913 to 0.989) simultaneously recorded during exercise. We conclude that BFI is a reliable and minimally invasive tool for evaluating relative changes in respiratory and locomotor muscle perfusion from rest to peak exercise in COPD patient groups.