How does the 4-7-8 breathing technique work?

You inhale for four counts, hold for seven, and exhale for eight. The long exhale and the extended hold slow your breathing rate substantially. A 2022 study of 43 healthy adults aged 19 to 25 found measurable immediate effects: heart rate and systolic blood pressure dropped in both groups, and in the non-sleep-deprived group high-frequency heart rate variability rose while low and very-low frequency power fell. That study measured physiology straight after the exercise rather than sleep or anxiety outcomes over time, and 4-7-8 was not included in the Stanford comparison trial.