The vagus nerve is the longest cranial nerve in your body, running from your brainstem through your neck, heart, lungs, and digestive system. It's the primary channel through which breathing exercises produce their calming effects. When you extend your exhale, the diaphragm pushes up and directly stimulates the vagus nerve, triggering a cascade of parasympathetic responses: heart rate drops, blood pressure lowers, and inflammatory markers decrease.
This timer uses extended exhale breathing (4 seconds in, 8 seconds out) — the pattern with the strongest vagal stimulation per breath. The 2:1 exhale-to-inhale ratio creates maximum diaphragmatic pressure during the exhale phase, which is when vagal stimulation is highest. Five minutes of this practice measurably increases vagal tone.