Slow breathing using pursed-lip exhales or a resistance device both potentially improve cardiovascular health, but pursed-lips breathing is free, more pleasant, and provides a better sense of control.
Oral and Systemic Effects of Breathing Patterns: Nasal Breathing vs. Mouth Breathing
Influence of a 30-Day Slow-Paced Breathing Intervention Compared to Social Media Use on Subjective Sleep Quality and Cardiac Vagal Activity
Slow-Paced Breathing: Influence of Inhalation/Exhalation Ratio and of Respiratory Pauses on Cardiac Vagal Activity
Effects of voluntary slow breathing on heart rate and heart rate variability: A systematic review and a meta-analysis (2022)
Benefits from one session of deep and slow breathing on vagal tone and anxiety in young and older adults (2021)
Oxygen-induced impairment in arterial function is corrected by slow breathing in patients with type 1 diabetes (2017)
Review: Can yoga breathing exercises improve glycemic response and insulin sensitivity? (2017)
How Breath-Control Can Change Your Life: A Systematic Review on Psycho-Physiological Correlates of Slow Breathing (2018)
A pilot study on the kinetics of metabolites and microvascular cutaneous effects of nitric oxide inhalation in healthy volunteers (2019)
Device and non-device-guided slow breathing to reduce blood pressure: A systematic review and meta-analysis (2019)
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.