Standing Up Out Of Respect During Krias Shema

The Mishna in Brachos details when one is permitted to interrupt his own reading of Krias Shema to say hello or answer to someone out of respect or out of fear. Nevertheless the Mishna Brura (66:2) brings from the Mogen Avrohom that nowadays we do not interrupt Shema to talk to anyone under normal circumstances. What about standing out of respect for a Rebbi or parent? Can we and should we stand up during Krias Shema or is that also no longer permitted? Rav Moshe Shternbuch (Tshuvos V'Hanhagos 4:22) weighs a number of reasons not to stand and dismisses them. He says that the Oseik BaMitzva Patur Min HaMitzva does not excuse you in this case since not standing up is an issur since it is embarrassing to a Talmid Chochom or parent to sit while they walk by. Furthermore Oseik BaMitzva Patur Min HaMitzva only exempts you when the second mitzva will disturb you from the first, which is not the case here when all you must do is stand up for a moment. Rav Shternbuch, after discussing other reasons to not stand, concludes that the only excuse not to stand for a talmid chochom is if it will really disturb your concentration during Shema, which most of us cannot claim today. Therefore one should, if he can, grab this great mitzva of standing for a talmid chochom or parent and get back to Shema. Moreover he says the mitzva should be done properly and one should stand up to his complete height rather than just slightly raise himself. [From Revach.net]