As connected with objects, it is motion; and Vishnu is there the presiding deity. The Apana air, whose motion is downward, as connected with the soul, is called the lower duct.
अधिभूतं तु गन्तव्यं विष्णुस्तत्राधिदैवतम्। अवाग्गतिरपानश्च पायुरध्यात्ममुच्यते॥