Slow breathing between 6 to <10 breaths a minute, with or without a device, for at least 10 minutes a day for 4+ weeks significantly reduces blood pressure, improves blood flow to vital organs, and improves autonomic dysfunction in people with hypertension or prehypertension.
Psychophysiological Responses to Various Slow, Deep Breathing Techniques
Slow-Paced Breathing: Influence of Inhalation/Exhalation Ratio and of Respiratory Pauses on Cardiac Vagal Activity
Benefits from one session of deep and slow breathing on vagal tone and anxiety in young and older adults (2021)
Heart rate variability biofeedback in chronic disease management: A systematic review (2021)
HRVB (and, hence, slow breathing) is a powerful adjunctive therapy for managing a wide variety of chronic diseases. To be effective, it should be practiced for a minimum of 10 min/day (but probably 20+ for best results—see next section). More broadly, this study supports using slow breathing at around 5-6 breaths per minute in people with chronic diseases.