bāhya-ābhyantara-viṣaya-ākṣepī caturthaḥ
The fourth state [of prāṇāyāma] transcends the field of exhalation and inhalation
Logic dictates that there are three parts to the breath: (i) inhalation; (ii) exhalation; and (iii) the pauses in between the inhalation and exhalation. Here Patanjali tells us that there is a fourth state to the breath, which takes you beyond the mind. In this place, the mind is so calm that it transcends the usual noise by putting it to one side and finding a relaxing space.
When you observe and lengthen your breath for the first time you experience the calmness that it brings. There are numerous techniques teaching you how to lengthen your breath and add pauses in between the breaths to guide energy into your body. For a detailed guide on the practice of prāṇāyāma see: So what is pranayama? (pranavashyauk.com)
Damian Cadman-Jones is an authorised teacher of Prana Vashya Yoga™