The exhale is the "brake" of the nervous system. Techniques that emphasize long exhales (like the 4-7-8 method or Physiological Sigh) activate the parasympathetic branch within seconds. This is the fastest way to exit a "panic" state.

Regular practice increases Carbon Dioxide tolerance, which correlates with lower anxiety levels.

Hyperventilation (blowing off too much CO2) is a primary trigger for panic attacks because it changes blood pH (respiratory alkalosis). Slow, measured breathing (like Box Breathing) restores CO2 levels and instantly signals safety to the brainstem.

The "physiological sigh" (two inhales, one long exhale) specifically reinflates collapsed alveoli in the lungs, offloading maximal CO2. This rapid drop in CO2 concentration signals the amygdala that the "suffocation threat" is over.