2.3.1. Low-Frequency Components

The adjustment of blood pressure and R–R intervals (the interval between consecutive heart beats; RRI) in the low-frequency domain mainly represents the sympathetically modulated mutual interrelation between the two. There were no group differences in resting levels of the synchronization variables γSBPxRRI,LF, γDBPxRRI,LF, and γSBPxDBP,LF (baseline; *F*(2,121) = 0.8, *p* = 0.461; *F*(2,121) = 0.7, *p* = 0.516; *F*(2,121) = 0.6, *p* = 0.567). Furthermore, the groups did not differ in their stress responses in these variables (Table 3).

**Table 3.** Phase synchronization indices of the low-frequency (LF) components (mean ± SD) of participants, and statistical results for group differences in response to the stress manipulation. CO: women without gestation during the last three years; UP: women with uncomplicated pregnancies; PE: women with a history of preeclampsia; γ: synchronization index; SBP: systolic blood pressure, DBP: diastolic blood pressure; RRI: R–R intervals.


Women with mild vs. severe preeclampsia did not differ in these variables (baseline, all *p* values >0.768; period x PE-group, all *p* values >0.271; period, all *p* values >0.446). No significant results were seen for women with early, preterm, and term preeclampsia (baseline, all *p* values >0.460; period x PE-time, all *p* values >0.098; period, all *p* values >0.591) either.

2.3.2. High-Frequency Components

The adjustment of blood pressure, R–R intervals, and respiration in the high-frequency domain represents the parasympathetically modulated mutual interrelations. In resting conditions, the groups did not differ in the synchronization variables γSBPxRRI,HF, γDBPxRRI,HF, γRESPxRRI,HF, γRESPxSBP,HF, and γRESPxDBP,LF (baseline, *F*(2,121) = 0.9, *p* = 0.43; *F*(2,121) = 0.5, *p* = 0.624; *F*(2,121) = 0.1, *p* = 0.917, *F*(2,121) = 0.2, *p* = 0.795; *F*(2,121) = 0.7, *p* = 0.523). No significant differences were observed in the changes of these variables during the stress manipulation (Table 4). However, some statistical trends emerged for the adjustment of respiration and blood pressure, which seemed to be attributed to the women affected by preeclampsia.

**Table 4.** Phase synchronization indices of the high-frequency (HF) components (mean ± SD) of participants, and statistical results for group differences in response to the stress manipulation. CO: women without gestation during the last three years; UP: women with uncomplicated pregnancies; PE: women with a history of preeclampsia; γ: synchronization index; SBP: systolic blood pressure, DBP: diastolic blood pressure; RRI: R–R intervals; RESP: respiration.


Women with mild vs. severe preeclampsia did not differ in these variables (baseline, all *p* values >0.199; period x PE-group, all *p* values >0.712 except for adjustment of respiration and R–R intervals, *p* = 0.084, and for respiration and systolic blood pressure, *p* = 0.100; period, all *p* values >0.199). Women with early, preterm, and term preeclampsia did not differ in these variables (baseline, all *p* values >0.649; period x PE-time, all *p* values > 0.162; period, all *p* values > 0.571).
