Proponents of a graduated concept of protection are e.g.:

Lockwood, M. (1985). The Warnock Report: a philosophical appraisal. In M. Lockwood (Ed.), Moral Dilemmas in Modern Medicine (pp. 153-186). Oxford University Press.

Sass, H. (1989). Hirntod und Hirnleben. In cf. (Ed.), Medizin und Ethik (pp. 160–183). Reclam.