As is commonly known, prana in the Vedas, in the Ayuvedic literature (which is sometimes associated with the sramana culture), as well as in later Hatha Yoga and later Indo-Tibetan Buddhism has connotations of “vital energy” and this affects how they approach meditation practice. Of course the term prana is known to have a broad semantic field even in the Vedas and thus it is beyond this post to focus on its varied meanings (and its associations with Atman-Brahman etc). For a good overview of Prana in the Vedas see: https://www.academia.edu/3589772/Vedic_and_Ayurvedic_Roots_of_the_Hatha_Yoga_Theory_of_Prana
While it is most common to see anapanasati as being “mindfulness of respiration” in modern Theravada circles, it seems that some modern teachers interpret the practice of anapanasati in a broader sense. One example would be Thanissaro Bhikkhu, who often speaks of being mindful of “breath energies” and so forth. Another example would be Chip Hartranft’s claims that the Buddha’s view of anapana is similar to the Vedic view of “vital energy” and cannot be restricted to just “respiration” (see “Awakening to Prana” in Freeing the Body, Freeing the Mind, available in google books). Of course Chip is most likely being influenced by his study of Yoga since he is also a yoga teacher focusing on Patanjali’s Yogasutra. This perspective is also quite common in modern vajrayana teachings on breath meditation.
I find this an interesting perspective because my own practice tends to reflect this, mainly, that paying attention to respiration leads one to also pay attention to various “breath energies”. I don’t mean this in a vitalistic sense or in the sense of supernatural/unscientific claims of energy like reiki and so on, but in the sense of the perceptions and sensations felt in the body which are related to but are not exactly respiration itself (muscular movements which aid in respiration for example, and the circulation of the blood felt particularly in the heart). Now it seems like the perception of these physical processes would technically not be called anapanasati by most, but it is not clear why this is the case, because it is possible to see the circulation of the blood for example as a continuation of the spreading of oxygen to the rest of the body. That is to say, why must anapanasati stop at the point of the absorption of oxygen into the lungs?
I guess my question is, is it possible to interpret anapanasati is the broader sense of ‘vital processes associated with respiration’ from the EBT evidence, or are the texts perfectly clear that anapana is strictly just “respiration”?