Objectives The objective of this study was to investigate the effects of slow breathing rate on heart rate variability (HRV) and blood pressure variability (BPV) in healthy subjects.
Methods 53 healthy volunteers underwent three periods of controlled breathing at 8, 12 and 16 breaths/min. ECG (RR), respiratory and blood pressure signal were continuously and simultaneously recorded. In our study, the influence of the respiration on RRI (RR interval) and BP were observed. Simultaneously, we studied the effects of slow breathing rate on RRI, amplitude of blood pressure oscillation, low-frequency (LF) power, high-frequency (HF) power and LF/HF of HRV and BPV. Then we also corrected the effects of slow breathing rate on respiratory peak shifts.
Results RRI and BP cyclical change coincided with the respiratory cycle; As breathing rate reduced, amplitude of RRI and blood pressure oscillation increased, heart rate slowed (P < 0.05), respiratory peak shifted towards left (P < 0.05). Compared to 16 breaths/min, routine spectral analysis showed increased LF and HF (P < 0.05) power, deceased LF/HF (P < 0.05) of HRV, increased LF, HF power (P < 0.05) and LF/HF of BPV in 12 breaths/min; It also showed increased LF power and LF/HF (P < 0.05), deceased HF power (P < 0.05) of HRV and BPV in 8 breaths/min. As the respiratory frequency decrease, correct spectral analysis showed increased HF power, deceased LF power and LF/HF (Significant respiratory rate effects were found in HF power, LF/HF of HRV and BPV in 8, 12 breaths/min and LF power of HRV in 8 breaths/min, P < 0.05).
Conclusions Reductions of respiration rate shifted the respiratory peak into the junction of HF and LF or even below LF range. In accordance with this shift, the effects of slow breathing rate on respiratory peak shifts should be corrected when we performed HRV and BPV spectral analysis; Correct spectral analysis demonstrated that slow respiration can cause increase in HF power and decease in LF power and LF/HF. These demonstrated that slow breathing is indeed capable of increasing vagal activities and shifting sympathetic-vagal balance towards vagal activities.