詳しいガイド（英語）
Meaning and tradition
Vishnu is the preserver in the Hindu trinity, and the mudra is named for him, also being called Nasagra Mudra, from nasa, “nose,” and agra, “tip.” Classical hatha yoga texts describe closing the nostrils with the fingers during pranayama, and the Vishnu hand shape with the index and middle fingers folded is the common modern form taught for Nadi Shodhana. It is mainly a practical technique rather than a symbolic gesture. By the finger-element scheme, the thumb is fire and the ring finger is earth, and the folded index (air) and middle (space) fingers are put aside, which is why the shape is described as regulating air and space.
How to practice
Sit in Easy Pose, Lotus Pose, or Hero Pose with a tall spine. Rest the left hand on the knee. Fold the right index and middle fingers to the base of the thumb, keep the other three extended, and raise the right hand to the nose with the palm toward the face. Close the right nostril with the thumb and the left with the ring finger as the breath requires. This hand is used for Nadi Shodhana, also taught as Anulom Vilom, and for Chandra Bhedana and Surya Bhedana, single-nostril breaths. Practice for 5 to 15 minutes.
Tips and common mistakes
The folded fingers are index and middle, and the extended fingers are thumb, ring, and little. The palm faces the face, and only the right hand is used.
Unlike Vayu Mudra, where only the index finger folds to the base of the thumb and the other three fingers are extended, Vishnu folds both the index and middle fingers.
Unlike Shunya Mudra, where only the middle finger folds under the thumb, Vishnu folds both the index and middle fingers to the base of the thumb.
Unlike Apana Vayu Mudra, where the index finger is folded and the thumb tips touch the middle and ring fingertips, Vishnu leaves the thumb, ring, and little fingers extended and uses the hand to close the nostrils.
Keep the elbow down and the shoulder relaxed, and use gentle finger pressure.
Tradition vs. evidence
Mudras have little clinical research behind them, and the claims about balancing the energy channels for this one are traditional. What is defensible is that this hand shape is a practical tool for closing one nostril at a time, and that the ritual of the hand movement can help pace a slow breathing practice.