Slow paced breathing is an effective tool for cardiac vagal activation. - GreenMedInfo Summary

OBJECTIVE: Changes in heart rate variability (HRV) associated with breathing (respiratory sinus arrhythmia [RSA]) are known to be parasympathetically (vagally) mediated when the breathing rate is within the typical frequency range (9-24 breaths/min; high frequency HRV). Slow yogic breathing occurs at rates below this range and increases low frequency HRV power, which may additionally reflect a significant sympathetic component. Yogic breathing techniques are hypothesized to confer health benefits by increasing cardiac vagal control, but increases in low frequency HRV power cannot unambiguously distinguish sympathetic from parasympathetic contributions. The purpose of this study is to investigate the autonomic origins of changes in low frequency HRV power due to slow paced breathing.

METHODS: Six healthy young adults completed slow paced breathing with a cadence derived from yogic breathing patterns. The paced breathing took place under conditions of sympathetic blockade, parasympathetic (vagal) blockade, and placebo. HRV spectral power was compared under eleven breathing rates during each session, in counterbalanced order with frequencies spanning the low frequency range (4 to 9 breaths/minute).

RESULTS: HRV power across the low frequency range (4-9 breaths per minute) was nearly eliminated (p=0.016) by parasympathetic blockade (mean spectral power at breathing frequency (SD) = 4.1(2.1)) compared to placebo (69.5(8.1)). In contrast, spectral power during sympathetic blockade 70.2(9.1) and placebo (69.5(8.1)) were statistically indistinguishable (p=0.671).

CONCLUSIONS: These findings clarify the interpretation of changes in HRV that occur during slow paced breathing by showing that changes in low frequency power under these conditions are almost entirely vagally-mediated. Slow paced breathing is an effective tool for cardiac vagal activation.