The present study investigated the association of near-infrared spectroscopy (NIRS) signals with systemic hemodynamic changes (SHCs) that can exert confounding effects on brain function analysis. NIRS and SHC parameters - basal thoracic impedance (Z_0), mean arterial pressure (MAP), total peripheral resistance, cardiac output, heart rate and stroke volume - were measured in 13 male subjects. Periodical SHCs were generated using four different periodical changes in sinusoidal lower body negative pressure (12.86, 18, 30 and 90 sec of 0 to -40 mmHg). The frequency response of gain of NIRS signals against Z_0 showed high-pass filter characteristics, however, that of gain against MAP showed low-pass filter characteristics. These results suggest that a compensatory model of NIRS against SHCs needs to consider the frequency characteristics of cardiovascular regulation.
