Parasympathetic blockade nearly eliminated low-frequency HRV power during slow-paced breathing compared with placebo (4.1 vs 69.5; p=0.016), showing changes are almost entirely vagally mediated.
RCT (n=6)
Counterbalanced order
Does slow-paced breathing under autonomic blockade alter low-frequency heart rate variability in healthy young adults compared to placebo?
Changes in low-frequency heart rate variability during slow-paced breathing are almost entirely vagally mediated, confirming it as an effective tool for cardiac vagal activation.
Absolute Event Rate: 4.1% vs 69.5%
p-value: p=0.016
OBJECTIVE: Changes in heart rate variability (HRV) associated with breathing (respiratory sinus arrhythmia) are known to be parasympathetically (vagally) mediated when the breathing rate is within the typical frequency range (9-24 breaths per minute bpm; 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 aim of this study was 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 11 breathing rates during each session, in counterbalanced order with frequencies spanning the low-frequency range (4-9 bpm). RESULTS: HRV power across the low-frequency range (4-9 bpm) was nearly eliminated (p = .016) by parasympathetic blockade (mean (SD) spectral power at breathing frequency = 4.1 (2.1)) compared with placebo (69.5 (8.1)). In contrast, spectral power during sympathetic blockade 70.2 (9.1) and placebo (69.5 (8.1)) was statistically indistinguishable (p = .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.
Kromenacker et al. (2018) conducted an RCT in Healthy (n=6). Parasympathetic (vagal) blockade vs. Placebo was evaluated on HRV spectral power across the low-frequency range (4-9 bpm) (p=0.016). Parasympathetic blockade nearly eliminated low-frequency HRV power during slow-paced breathing compared with placebo (4.1 vs 69.5; p=0.016), showing changes are almost entirely vagally mediated.
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