Spectral analysis of heart rate variability as a quantitative measure of parasympatholytic effect-integrated pharmacokinetics and pharmacodynamics of three anticholinergic drugs - Scheinin,H.; Helminen,A.; Huhtala,S.; Grönroos,P.; Bosch,J.A.; Kuusela,T.; Kanto,J.; Kaila,T. (Ther Drug Monit, 1999)