Anger often grows after the moment that started it, with nothing new added. The system amplifies its own signal, insisting that this is big, pay attention, react.

What the research says

A meta analysis of randomised studies found that training people to breathe slowly at their own resonant rate produced moderate improvements in anxiety, depression and performance measures. The effect sits on the body's regulation rather than on the argument you are having. Most of those trials involved repeated practice sessions, so this works better as something already rehearsed than as a rescue you try for the first time mid row.

Strength of evidence: one line of research. A single study, or a theoretical account.