Fig. 4.

Onset time differences at the breakpoints of rMAP, rCBF, $\mathrm{r}[{\mathrm{HbO}}_2]$, r[Hb], and rTHC relative to rMAP in the presyncopal group. The asteroids with error bars represent the group $\text{means}\pm \text{standard deviations}$. The dashed horizontal line represents 0 s. The negative/positive value below/above the dashed horizontal line (0 second) indicates that the breakpoint of cerebral hemodynamic parameters (i.e., rCBF, $\mathrm{r}[{\mathrm{HbO}}_2]$, r[Hb], and rTHC) occurred earlier/later than that of rMAP.