“…This is to say, a slope of zero would imply perfect autoregulation where CBF remains constant across the entire range of MAP, while a gain equal to 1 would reflect the total absence of autoregulation (Tzeng et al, 2010b). The limitations inherent to any pharmacological approach remain manifest with this technique, and although there is supportive evidence (Greenfield and Tindall, 1968) the assumption that there is no direct drug-effect on the cerebral vasculature has been questioned (Brassard et al, 2010). However, direct effects of PE and SNP on cerebral vasculature are considered unlikely given that the blood-brain barrier normally prevents endogenous circulating catecholamine from binding to ␣ 1 -adrenoreceptors in small cerebral vessels (Mackenzie et al, 1976;McCalden et al, 1977;Ainslie and Tzeng, 2010).…”