I believe it is important to directly quote the FDA about design inputs (ISO 13485:2003)

Inputs relating to product requirements shall be determined and records maintained. These inputs shall include:
a) functional, performance, and safety requirements, according to the intended use,
b) applicable statutory and regulatory requirements,
c) where applicable, information derived from previous similar designs,
d) other requirements essential for design and development, and
e) output(s) of risk management
These inputs shall be reviewed and approved.
Requirements shall be complete, unambiguous, and not in conflict with each other.