Figure 2From: Altered autonomic nervous system activity as a potential etiological factor of premenstrual syndrome and premenstrual dysphoric disorderExamples of ECG R-R interval changes and the corresponding power spectra during the follicular and late luteal phase for subjects in the Control, PMS, and PMDD groups. LF: low frequency power (0.03–0.15 Hz); HF: high frequency power (0.15–0.5 Hz).Back to article page