Abstract
Controlled breathing maneuver is being widely applied for cardiovascular autonomic control evaluation and cardiac vagal activation through reduction of breathing rate (BR). However, this maneuver presented contradictory results depending on the protocol and the chosen BR. These variations may be related to the individual intrinsic profile baseline sympathetic tonus, as described before by others. In this study, we evaluated the effect of controlled breathing maneuver on cardiovascular autonomic control in 26 healthy subjects allocated into two protocols: (1) controlled breathing in three different rates (10, 15, and 20 breaths/min) and (2) controlled breathing in rates normalized by the individual spontaneous breathing rate (SBR) at 100, 80, 70, and 50%. Our results showed autonomic responses favorable to vagal modulation with the lower BR maneuvers. Nevertheless, while this activation was variable using the standard protocol, all participants of the normalized protocol demonstrated an increase of vagal modulation at 80% BR (HFnu 80 = 67.5% vs. 48.2%, p < 0.0001). These results suggest that controlled breathing protocols to induce vagal activation should consider the SBR, being limited to values moderately lower than the baseline.
Highlights
Controlled breathing maneuver is a methodology widely used to evaluate cardiovascular autonomic control (Pinna et al, 2006; Adams et al, 2009; Stein et al, 2011; Porta et al, 2012; Ferreira et al, 2013; Krasnikov et al, 2013)
The total spectral power value, which reports the value of heart rate variability (HRV), was not changed, the maneuver in 10 breathe/min evoked changes related to the spectral components with increased high frequency (HF) band, compared to Basal, R15 and R20 blocks, both in absolute (p = 0.022, p = 0.015, and p = 0.011, respectively), and in normalized (p = 0.041) values (Figure 1)
The low frequency (LF)/HF ratio, which is related to sympathetic-vagal balance, was lower in the R10 block in comparison to R15 and R20 (p = 0.028) blocks
Summary
Controlled breathing maneuver is a methodology widely used to evaluate cardiovascular autonomic control (Pinna et al, 2006; Adams et al, 2009; Stein et al, 2011; Porta et al, 2012; Ferreira et al, 2013; Krasnikov et al, 2013). The standardization of a normalized breathing control protocol to induce vagal activity depends on a systematic investigation of the effects of controlled breathing maneuver on cardiovascular autonomic control. This standardization would be relevant to the evaluation of the cardiovascular autonomic control, and to the improvement of vagal modulation as a potential therapy for many diseases (Bernardi et al, 2001; Grossman et al, 2001; Joseph et al, 2005). In this study we applied spectral methods to evaluate the effects of controlled breathing maneuvers on cardiovascular autonomic control in healthy subjects with different breathing rates (from 6 to 22 breaths/min), fixed or normalized to spontaneous breathe. A standard protocol, based on the normalization of individual SBR, can enhance vagal activation and this standardization could improve the efficiency and clinical applicability of vagal modulation protocols
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