# Effect of Controlled Expiratory Pressures on Cerebrovascular Changes During Valsalva Maneuver
## 4 Discussion  
Overall, this study demonstrated that two expiratory pressures, 30 and 40 mmHg VM, resulted in significant changes in CCA blood velocity, PWV, and brain hemodynamics. In particular, HR and RI changed significantly only at a 40 mmHg VM. Therefore, it can be  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Repeated Measure Comparisons**} & \multicolumn{6}{c}{**Post Hoc Comparisons (Scheffe)**} \\ \hline
**Outcome Variable** & **Testing** & **Mean \(\pm\) SD** & **F** & \(p\) & **Testing** & **T** & \(p\) \\ \hline \multirow{8}{*}{\(\tau\)SO2} & \multirow{8}{*}{Lt} & PRE & 66.97 \(\pm\) 11.13 & \multirow{8}{*}{0.21} & \multirow{8}{*}{0.792} & \multirow{8}{*}{0.792} & VM & 0.60 & 0.948 \\  & & VM & 66.64 \(\pm\) 10.05 & & & & & POST1 & 0.13 & 0.999 \\  & & POST1 & 66.89 \(\pm\) 10.16 & & & & & POST2 & \(-\)0.05 & 1.000 \\  & & POST2 & 67.01 \(\pm\) 10.10 & & & & & POST1 & \(-\)0.67 & 0.930 \\  & & & POST2 & 67.01 \(\pm\) 10.10 & & & & & POST2 & \(-\)0.78 & 0.894 \\  & & & & & & & & POST1 & POST2 & \(-\)0.48 & 0.972 \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\
30 mmHg & & & & & & & & & & \\ \hline \multirow{8}{*}{\(\tau\)SO2} & \multirow{8}{*}{Lt} & PRE & \(-\)0.02 \(\pm\) 0.09 & \multirow{8}{*}{3.97} & VM & \multirow{8}{*}{0.037 \(\star\)} & VM & 1.92 & 0.323 \\  & & VM & \(-\)0.03 \(\pm\) 0.08 & & & & & POST2 & 2.83 & 0.072 \\  & & POST1 & \(-\)0.03 \(\pm\) 0.08 & & & & & POST1 & \(-\)0.20 & 0.998 \\  & & POST2 & \(-\)0.03 \(\pm\) 0.08  
concluded that there were differences between the biosignals according to the intensity of expiratory pressure. Both the 30 and 40 mmHg VM achieved an improvement in PWV and an increase in PSV. After VM at the two pressures, the PSV significantly increased in POST2, corresponding to VM phase IV. Phase IV of VM involves a blood pressure overshoot above baseline levels [4,29], leading to an increase in the blood velocity. In fact, according to previous research, the change in cerebral blood velocity following VM showed the greatest increase in phase IV [30]. Temporary changes in PWV can occur because the VM can stimulate the vascular tone. Vascular tone increases as blood pressure increases to protect blood vessels. In phase III, decreased blood pressure and increased venous return can cause vasodilation and decreased vascular tone [9,15]. Similarly, changes in vasoconstriction and dilation have been reported during resistance exercises accompanied by VM [19,31,32]. Even at 30 mmHg VM, in this study, both the PWV and stiffness index were significantly reduced, indicating an immediate effect of alleviating vascular stiffness. A significant decrease in PWV was also observed at 40 mmHg VM, but only a slight decrease in stiffness index was observed, which was not statistically significant. Furthermore, the PRE and POST differences in PWV and stiffness index at 40 mmHg VM were relatively smaller than those at 30 mmHg VM. Thus, the temporary effect of the VM on vascular stiffness may be greater at 30 mmHg than at 40 mmHg. This seems to be because the relatively high hypertensive stimuli induced excessive baroreflex activation at 40 mmHg VM, which increased sympathetic nerve activity and suppressed vasodilation. Previous studies have reported that as the intensity of the VM increased to 10 mmHg, 40 mmHg, and 60 mmHg, the rate of increase in heart rate during Phase IIa correspondingly increased [33]. This suggests that higher pressure intensities lead to enhanced sympathetic activity through the baroreflex. As with the results of previous studies, a significant increase in HR and RI appeared only in 40 mmHg VM. In contrast, a previous study reported an increase in vascular stiffness following the VM, which differs from the finding of this study [34]. This discrepancy may be due to the fact that the referenced study involved repeated VMs and measured vascular stiffness 20 min afterward.