This is an excerpt of Dhāraṇā 2 from the Vijnana Bhairava: The Manual for Self Realization, revealed by Swami Lakshmanjoo...
भैरवि व्यज्यते वपुः ॥२५॥
bhairavi vyajyate vapuḥ // 25 //
Antar bahir, internally or outwardly (vāpi means “or”), internally or outwardly, marutaḥ, this energy of breath when [it] is followed by two voids [i.e.] by returning back to two ethers, viyat yugma ānuvartanāt (by maintaining the uninterrupted awareness there means bhairavyā, by means of Bhairavī; Bhairavī means uninterrupted awareness), when you maintain uninterrupted awareness in these two voids, internally and externally (there is an internal void and an external void); ithaṁ, by this way of treading on this process (ithaṁ, by this way), bhairavasya vapuḥ vyajyate, the formation of the svarūpa of Bhairava is revealed, vyajyate.
Bhairavī is āmantraṇa [vocative]: “O Bhairavī! O Pārvatī!”
Here you have not to recite “so” or “haṁ”. It is without the recitation of “sa” and “ha”.
It is only awareness that functions here. It is why this is śāktopāya. This can’t be āṇavopāya because you have to maintain awareness only, no recitation of mantra. Only you have to intake and outcome of breath, and see where are these two voids.
ALEXIS: Between going out and coming in?
SWAMIJI: Between going out and coming in. Here and in the heart.
JOHN: In āṇavopāya there is object.
SWAMIJI: Because the object there is mantra also.
JOHN: But there is not object here.
SWAMIJI: There is no object. It is why it is called here śāktopāya.
41. Swamiji preferred anuvartanāt to anivartanāt, which is found in some readings. [Editor's note]