There are two interesting quotations in the entry written by Catherine Despeux and I would like to put them as closer as possible:
(1) — “Tiaoqi usually refers to methods for regulating the outer breathing. These exercises are often performed before breath control and retention, and allow one to concentrate the mind and reach a state of quiet. Inspiration always occurs through the nose, called Gate of Heaven, and expiration through the mouth, called Door of Earth (tiānmén 天門 and dìhù 地戶). Breathing should be subtle and inaudible.”
(2) — “Strictly speaking, the tiaoqi method consists of inhaling and exhaling until breathing becomes regular, and of ingesting the regulated breath. However, tiaoqi sometimes refers to regulating and harmonizing inner breath. Examples of this practice are found in the Qianjin fang and in Taiqing tiaoqi jing.”
What I am trying to underline here is the similarity between outer and inner breathing techniques and the lack of tension in their interpretation: doing one of them we are doing another, and that is a relief, I guess.