Fig. 2. Changes (mean ± SEM) in approximate entropy (ApEn) of (A ) forehead skin blood flow (LDFforehead) and (B ) finger skin blood flow (LDFfinger) in all subjects during nonpulsatile cardiopulmonary bypass. LDFforeheadsignal regularity progressively increases during nonpulsatile cardiopulmonary bypass as measured by a decrease in approximate entropy.