What does Diaphragmatic Breathing do to the body?
The most consistent changes are a slower heart rate and slower breathing, both measured to fall during and after practice (Yu-Fen et al., 2017). Heart-rate variability, a marker of the calming branch of the nervous system, has been recorded rising in the same window, which the body registers as settling and softening (Stromberg et al., 2015). One trial in healthy adults also linked eight weeks of practice with lower cortisol, the body's main stress hormone, a shift that tends to feel like less wired, on-edge tension (Ma et al., 2017).
Blood Pressure
direct EVIDENCE
When you feel braced and wound up under pressure, slow diaphragmatic breathing at around six breaths a minute can ease that tension and let blood pressure, the force of blood pushing against your artery walls, settle. In one study of people living with chronic pain, those who kept up the practice showed less blood-pressure spiking under a stress test (Schmidt et al., 2013), which many people feel as a loosening in the chest and shoulders and a sense that the body has stopped bracing.
Respiratory Rate
direct EVIDENCE
Many people feel the breath drop lower into the belly, the exhale lengthening, and the fast, high-in-the-chest breathing of stress easing into a slower rhythm. That change shows up as a lower respiratory rate, the number of breaths you take each minute, which studies of slow belly breathing have measured alongside calmer stress signals (Ma et al., 2017), (Yamaguti et al., 2012).
Parasympathetic Tone
direct EVIDENCE
As the body settles, breath slowing and shoulders loosening, that ease reflects a rise in parasympathetic tone, the rest-and-recovery activity of the nervous system. Slow diaphragmatic breathing has been measured raising heart-rate variability, a marker of that calming branch, in motion-sickness-prone adults (Stromberg et al., 2015), and improving cardiac autonomic function in chronic pain patients who practised consistently (Schmidt et al., 2013).
