Webster’s 1913 has no entry under this spelling.
Shades of meaning
Fernald has no entry of its own for hold up; he lists it under support.
Where he writes about it:
Support and sustain alike signify to hold up or keep up, to prevent from falling or sinking; but sustain has a special sense of continuous exertion or of great strength continuously exerted, as when we speak of sustained endeavor or a sustained note; a flower is supported by the stem or a temple-roof by arches; the foundations of a great building sustain an enormous pressure; to sustain life implies a greater exigency and need than to support life; to say one is sustained under affliction is to say more both of the severity of the trial and the completeness of the upholding than if we say he is supported. — from support