Cardiac interbeat interval dynamics from childhood to senescence: comparison of conventional and new measures based on fractals and chaos theory - Pikkujamsa, SM; Makikallio, TH; Sourander, LB; Raiha, IJ; Puukka, P; Skytta, J; Peng, CK; Goldberger, AL; Huikuri, HV (Circulation, 1999)