sympathovagal balance (Raghurajet al. 1998). Studies on conscious breath alterations are of particular interest as the integrative role of respiratory and cardiovascular rhythms have been understood in yogic contexts as the ability of breath regulation to influence brain function (Gilbert 1999). Practitioners of HFYB have described the effects as energizing, cleansing, and mind-clearing (Gilbert 1999). High frequency yoga breathing has been associated with an increase in vigilance and attention, both with and without sympathetic nervous system modulation (Telles, Singh and Balkrishna 2011). Hence, the effects of HFYB on HRV have been an avenue to examine its impact on practitioners (Telles, Singh et al. 2011). In a study comparing slow breath work to HFYB, Raghuraj et al. (1998) found no significant change in participants’ (n=12) HRV after slow breathing. However, after the HFYB practice, participants’ (n=12) measurements showed an immediate increase in the LF component, a decrease in the HF component, and an increase in the LF/HF ratio after one minute of practice. Rhaghuraj et al. (1998) interpreted these results as showing that, after HFYB, there was an increase in sympathetic nervous system activation and a decrease in vagal efferent activity. In a later study, Telles and Singh et al. (2011) compared the effects of both HFYB and breath awareness (BAW) on HRV. Breath awareness is simply sitting and witnessing the breath (Telles et al. 2015). Telles and Singh et al. (2011) compared the two practices, for it is understood that BAW alone improves attention, and BAW is part of HFYB practice. The researchers measured effects before, during, and after the participants’ (n=38) breath practices. The practice time for each form of practice consisted of three, five minute increments. The recorded HRV and respiration changes for both practices were associated with reduced parasympathetic modulation, but the magnitude of change was greater for HFYB during the practice, while for BAW it was greater after. Measures of time domain also showed that, during and after HFYB, vagal modulation decreased. The same trend was found after, but not during, BAW (Telles and Singh et al. 2011). For this same study, Telles and Singh et al. (2011) considered the hypothesized increase in sympathetic modulation to be plausible, as the state is associated with the vigilance linked to both breath practices. Interestingly, frequency domain analysis showed no significant change in the LF and HF variables for HFYB. The researchers interpreted the data as suggesting that HFYB induces a parasympathetic withdrawal, but not the sympathetic activation that would be expected to simultaneously occur. Given the lack of sympathetic modulation increase during HFYB, the author suggested that reports on enhanced attention and performance tasks are due to shifts, resulting from vagal withdrawal alone, especially from cardiac vagal modulation. They speculated that HRV changes may be due to conscious cortical influence on respiration, as there is a close association between cardiovascular and respiratory centers in the brainstem. The studies by Raghuraj et al. (1998) and Telles and Singh et al. (2011) support the finding that HFYB reduces vagal modulation and shifts autonomic balance to the sympaSpirituality Studies 2 (1) Spring 2016 39
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