Complex sentence: Exhalation lasts about twice as long as inhalation because the diaphragm relaxes more gently than it contracts during inhalation, this prevents undue narrowing of the airways, from which the air escapes more easily than from the alveoli.
Split into simpler sentences: Exhalation lasts about twice as long as inhalation because the diaphragm relaxes more gently than it contracts during inhalation. This prevents undue narrowing of the airways, from which the air escapes more easily than from the alveoli.