What details suggest that Dr. Manette's captivity has changed him in A Tale of Two Cities?

It is clear from Chapter Six of Book the First that the
long years of captivity have had an incredibly negative impact on the life of Dr.
Manette, as this chapter shows that he has lost all sense of his former identity, and
indeed of having any identity at all apart from being known as "One Hundred and Five,
North Tower," and mending shoes. Note the first description we are given of him as
Monsieur Defarge leads Mr. Lorry and Lucie Manette into his
room:

The
faintness of the voice was pitiable and dreadful. It was not the faintness of physical
weakness, though confinement and hard fare no doubt had their part in in it. Its
deplorable peculiarity was, that it was the faintness of solitude and disuse. It was
like the last feeble echo of a sound made long and long ago. So entirely had it lost the
life and resonance of the human voice, that it affected the senses like a once beautiful
colour faded away into a poor weak stain. So sunken and suppressed it was, that it was
like a voice underground. So expressive it was, of a hopeless and lost creature, that a
famished traveller, wearied out by lonely wandering in a wilderness, would have
remembered home and friends in such a tone before lying down to
die.

Note how this barrage of
description presents Dr. Manette as being literally a shadow of his former self. He has
not used his voice much at all, and his voice is compared to being a once vibrant colour
that is now nothing more than a pale "weak stain." His voice is reminiscent of death and
abandonment. The way in which he has no memory of being anything else than a prisoner
and a mender of shoes clearly shows the way that his captivity has impacted him mentally
as well as physically, reducing him to nothing more than a pair of "haggard eyes" and a
weak, frail, old man. It is only the love and care of his daughter that manages to
resurrect him, bringing him metaphorically back to life, as Mr. Lorry's cryptic message
explains.