Pran is the breath that is inhaled,
whereas
apan is the breath which moves out.

Sages have found by experience
that
along with breath
we also imbibe desires from surrounding environment
and,
similarly, transmit waves of inner pious
as well as
impious thoughts
with
our exhalations.

Non-assimilation of any desire
from an external source is the offering
of
pran as oblation,
whereas suppression of all inner desires
is
the sacrifice of apan,
so that there is generation of
neither
internal desire
nor
grief because of thoughts of the external world.

So when both pran and apan are properly balanced,
breath is regulated.

This is pranayam, the serenity of breath.
This is the state in which the mind is supreme,
for restraint of breath
is
the same
as
restraint of mind.

~Revered Gurudev Swami Adgadanand Jee Paramhans~