Fig. 4. Progressive changes (mean ± SEM) in (A ) forehead auto power spectral density (APSD^forehead) high-frequency (HF) band power and (B ) finger auto power spectral density (APSD^finger) low-frequency (LF) band power during nonpulsatile cardiopulmonary bypass. Values reported in normalized units (NU) obtained by expressing power in the LF and HF bands as percentage of total power in the 0.04–0.30 Hz range; *P < 0.05.