This is an interesting result, as taking a deep breath of air and expanding your chest is a way to active the vagus nerve and cause relaxation, but it will temp

This is an interesting result, as taking a deep breath of air and expanding your chest is a way to active the vagus nerve and cause relaxation, but it will temporarily increase your blood pressure. They give you warnings about it in descriptions of the exercise in case you have high blood pressure. This is apparently why it works. It's called the Valsalva maneuver: https://www.medicalnewstoday.com/articles/322661 https://www.medicalnewstoday.com/articles/322661