Is it true that brahma assigns certain number of breaths to each creature based on karma? Why it's breaths count and not time?
The breathing as a material bodily process, is more explicitly understood as an implicit function of what is referred within the paradigm of Hinduism as the ten Prāṇas - [Five Primary + Five Secondary] and together with the Mind, they are the personified representation of the 11 Rudras. According to the Yoga tradition, this far-reaching system of vital energy functions through five sub-energies called the prāṇa-vayus ( means “wind, breath, or life force”). Each function has a distinct role, and each is integrated into the total system of human energy.
Is the number of breaths allotted to an individual in a lifetime predetermined ?
Short Answer: Yes
Let's discuss this in the light of some scriptural and other relevant references:
In his "The Science of Prāṇāyāma" - Control of Breath, Sri Swami Sivananda observes that:
He who practises prāṇāyāma will have good appetite, cheerfulness, handsome figure, good strength, courage, enthusiasm, a high standard of health, vigour and vitality and good concentration of mind. Prāṇāyāma is quite suitable for the Westerners also. A Yogi measures the span of his life not by the number of years but by the number of his breaths. You can take in a certain amount of energy or prāṇa from the atmospheric air along with each breath. Vital capacity is the capacity shown by the largest quantity of air a man can inhale after the deepest possible exhalation. A man takes fifteen breaths in a minute. The total number of breaths comes to 21,600 times per day.
In the Pretakhaṇḍa of the Garuda Purana, it says:
O Tarkshya, thus, man is born in the mortal world as a result of his own actions. The five characteristics, viz. the span of life, action, wealth, learning and death are created in men even as they are in the womb. The life is born as they are in the womb. The life is born as a result of action; it is dissolved as a result of action. Happiness or misery, fear or welfare are the results of actions. The foetus lies in the womb with the feet up and the face downwards. The foetus lies in the womb with the feet up and the face downwards. The life takes its birth with its association brought about by its own actions.
Here, actions (Karma) have several connotations, and by that logic, breathing is also an action (even if it might be called as a pseudo-involuntary action sometimes, but still an action).
Similarly, The Bhūmi-khaṇḍa of the Padma Purana focuses on Karma as the prime-mover of destiny:
Of the fetus in the womb these five are seen: (span of) life, acts, wealth, learning and death. As the doer does (i.e. fashions different images from) a lump of clay, similarly acts that are performed grasp the doer.
And since, an individual's life is pre-determined, the concept of "pre-determinism" very well extends to the number of breaths too., since breaths (the total pre-determined lifespan) are not a part of Kriyamāna or āgāmi Karma but rather Prārabdha Karma, which constitutes our major life events (birth & death included, and thus the total breaths predetermined).
The Chandogya Upanishad (CD) says:
“Verily, indeed, all beings here enter with breath and depart with breath” [CD 1.11.5].
As an animal is attached to a chariot, even so is the Breath attached to this body”.
Because of breath the body moves (perform action) (“lives”). [CD 8.12.3]
And thus, when the pre-determined breaths are finished, the body ceases to move (“dies”).
“It is the breath that man brings here at birth and it is the breath that man takes with him when he leaves this world” (Verse 52).
Finally in The Prashna Upanishad 4:8, The absolute rulership of the breath in the individual is outlined as follows:
“Earth and the element of earth, water and the element of water, fire and the element of fire, space and the element of space, the organ and object of vision, the organ and object of hearing, the organ and object of smell, the organ and object of taste, the organ and object of touch, the organ and content of speech, the hands and the object grasped, the organ of generation and enjoyment, the organ of excretion and the excreta, the feet and the space trodden, the mind and the content of thought, understanding and the content of understanding, egoism and the content of egoism, awareness and the content of awareness, the shining skin and the object revealed by that–all that is held and controlled by Prāṇā (and thus, on the material level by the Breath)”. Finally the Upanishad (6:4) declares that the Supreme Self created the Breath, and from the Breath was created all the worlds and all that is within them. The same is true of the individual Self as well.
Moreover, in the Hiranyagarbha Sūktam [Rig Veda.121.], the breath ( prāṇa-vayus) are eulogized to be sanctioned by the Supreme and thus, pre-determined already.
hi̱ra̱ṇya̱-ga̱rbhas-sama̍varta̱tāgre̍ bhū̱tasya̍ jā̱taḥ pati̱reka̍ āsīt |
sa dā̍dhāra pṛthi̱vīṁ dyām u̱temāṁ kasmai̎ de̱vāya̍ ha̱viṣā̎ vidhema || 1 ||
- In the beginning arose Hiranyagarbha, the One Lord of all created >beings.
He established and supports this
earth and heaven. What God shall we adore with our oblation?
ya ā̎tma̱dā ba̍la̱dā yasya̱ viśva̍ u̱pāsa̍te pra̱śiṣa̱ṁ yasya̍ de̱vāḥ |
yasya̍ chā̱yā’mṛta̱ṁ yasya̍ mṛ̱tyuḥ kasmai̎ de̱vāya̍ ha̱viṣā̎ vidhema || 2 ||
- Giver of vital breath, of power and vigour, he whose teachings all the Gods acknowledge — The Lord of death, whose shade is immortality. What God shall we adore with our oblation?
Of-course, on can for the sake of argument, may bring forth the case of Mārkaṇḍeya Rishi, whose life (and thus, the number of breaths) were pre-determined to be terminated at 16. However, his infallible devotion to God Shiva, made him a Mṛtyuñjaya (conquerer of Death itself). But, these cases are exceptions and if one might be able to reach that level or not is another topic for an opinion based discussion QnA itself. It can be further argued, that maybe it was already pre-determined, for the whole episode involving Mārkaṇḍeya to occur in the way it occured.
Thus, again making the whole arguement in favor of the “pre-determinism of an individual's lifespan and thus the total number of breaths too.”