釋禪波羅蜜次第法門 3.26

3.26

若繫心鼻柱者，鼻是風門，覺出息、入息，念念不住，易悟無常。亦以扶本安般之習，心靜能發禪定。

If one ties the mind to the bridge of the nose, the nose is the gate of wind, and one perceives the outgoing breath and incoming breath, not remaining [fixed] from thought-moment to thought-moment, making it easy to awaken to impermanence. It also assists one's original practice of ānāpāna; when the mind is tranquil, it can arouse dhyāna-concentration.