I came across a very good posting by Krishnaswamy Narasimhan which Inspired to add this Posting the following.
Actually use of gayatri mantra with Vyahritis that is Bhu ,Bhuvah Suvah in performing anuloma viloma pranayama helps in doing it with the ratio of 1:3:2. Inhale through the left nostril reciting Om Bhuh Om Bhuvah   till dhiyoyonaprachotayat to complete puraka. Then commence reciting omapoh, Jyotirasoh to bhur bhuvah surom and again complete oneround from Om Bhuh till end to perform Kumbaka and recite From Om Bhuh to end  third time performing rechaka through right Nostril. Repeat above by inhaling through right nostril and exhale through left after performing Kumbaka as above.Normally three such round are performed during sandhya vandana after which one starts Gayatri mantra japa.This ensure equal flow of Breadth in Both the nostrils and activtes sushumna whccih enables the mind to Focus on the mantra while doing the Japa.This is the reason in most religious and vedic Karma after Prayer to Lord Ganesha one performs a pranayama as  above.But Today no one follows the correct procedure but it ha become a ritual to touch thenose and continue.