tDCS protocol and HRV
The results of our analysis revealed a significant effect of tDCS
protocol (chi-square (χ2) = 8.02, p = 0.018) in the RMSSD measure.
Post-hoc analyses revealed that HRV during 3.0mA tDCS, measured with
RMSSD, was significantly increased compared to sham (beta= -9.97,
standard error (SE) = 1.96, p < 0.001) and 1.5mA (beta= -7.92,
SE = 1.94, p = 0.001). No significant difference was found between 1.5mA
tDCS and sham (beta= -2.06, SE = 1.9, p = 0.28) (Figure 2A and Sup.
Material - Appendix 4). The interaction between tDCS protocol and time
is presented in the Sup. Material - Appendix 5.
The same results were found for the HF-HRV measure (tDCS protocol: χ2 =
6.88, p = 0.03). Post-hoc analyses revealed that HF-HRV were greater
with 3.0mA compared to sham (beta= -606, SE = 112, p < 0.001)
and 1.5mA (beta= -454, SE = 112, p = 0.001) (Figure 2B and Sup. Material
- Appendix 6). The interaction between tDCS protocol and time is
presented in the Sup. Material - Appendix 7.
No association was found between HRV changes and the interaction between
protocol and psychological state at the baseline (STAI: χ2 = 2.18, p =
0.33; VAS baseline: χ2 = 0.45, p = 0.79).
Figure 2. Effects of tDCS on HRV. A) Results of RMSSD; B) Results of
HF-HRV.