The short version
In through the nose for about 5, out for about 5, which is 10 seconds per full cycle. If five and five feels far at first, start at 4 and 4 and let it lengthen. For an extended stretch of low-grade pressure, like a meeting, a waiting room, or a long wait at a departure gate.
What the research says
Robust physiology: a ten-second breathing cycle drives the blood-pressure reflex in phase with itself. A 2022 meta-analysis of 223 studies found heart-rate variability rises during and after slow breathing, and pooled trials show resting blood pressure falls by a few points, which is why anyone on blood-pressure medication is asked to talk to their prescriber. A 2026 trial found a fixed six-per-minute worked as well as a personally measured rate. Cited under Chapter 5.
Rooms where it does the work
Two rules, no exceptions
Never practice any technique on this site while you are driving, operating machinery, or doing anything that needs your full attention. The slow ones can make you drowsy, faster than you’d expect. And never practice a breath-hold, bellows breath, or any vigorous breathing in or near water. Read Before you begin for the doctor’s list and the rest.
The short version is a reminder, not a lesson. The chapter has the story, the steps, the mistakes, and the limits.