This study investigated the fluctuations of autonomic nervous activities during the menstrual cycle. Twenty college females were tested for cardiovascular reactivity to mental challenge during both follicular and luteal phases across two menstrual cycles. Power spectral analysis of heart rate variability (HRV) was used to examine the autonomic nervous activities. At baseline, although heart rate and blood pressure did not differ across the menstrual cycle, the low-frequency (LF) component in the HRV was higher and the high-frequency (HF) component in the HRV was lower during the luteal phase than during the follicular phase. The LF/HF ratio was also significantly greater in the luteal phase. These data suggest that sympathetic nervous activities are predominant in the luteal phase as compared with follicular phase. In addition, the power spectral analysis of HRV has more sensitivity than heart rate or blood pressure in assessing the slight fluctuations of autonomic nervous activities during the menstrual cycle.

The purpose of the present study was to determine the fluctuation in cardiovascular reactivity to mental stress during the menstrual cycle by comparing heart rate variability (HRV), and other physiological and psychological data in females with those in males. Cardiovascular reactivity to two mental tasks was measured in 14 females during the follicular and luteal phase of menstruation over two menstrual cycles. The same tasks were subsequently given to a matched pair of males (Nϭ14), at the same intervals as their corresponding females. Heart rate, blood pressure and HRV were used as indices of cardiovascular reactivity. Subjective mental workload was measured at the end of each task. Power spectral analysis of HRV showed that the high frequency (HF) component in HRV decreased more during the luteal phase than the follicular phase. The low frequency (LF) component in HRV and the LF/HF ratio in the luteal phase were significantly higher than that in the follicular phase. The LF component and the LF/HF ratio were significantly lower in females than in males; conversely, the HF component was significantly higher in females than in males. Neither significant effects of menstrual cycle, gender and mental stress nor any significant interactions were found for mental workload. These findings indicate that sympathetic nervous activity in the luteal phase is significantly greater than in the follicular phase whereas parasympathetic nervous activity is predominant in the follicular phase. The results also suggest that predominance of sympathetic nervous activity in males compared with a dominant parasympathetic nervous activity in females.

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A study was performed on seven traumatic neurologically complete quadriplegic (QP) males and seven age-matched healthy males (control) while they were at rest in the supine position in a climatic chamber (temperature 30 degrees C, relative humidity 60%). Arterial blood pressure waveforms were measured by a continuous noninvasive blood pressure-monitoring system based on arterial tonometry. Furthermore, the spontaneous beat-to-beat systolic blood pressure (SBP) variabilities of subjects were investigated by means of autoregressive power spectral analysis. As shown by earlier studies with an invasive (intra-arterial) blood pressure-monitoring system, in the control group there were two major spectral components: a high-frequency (HF) component [center frequency 0.27 +/- 0.02 (SE) Hz eq, power 0.9 +/- 0.2 mmHg2] and a low-frequency (LF) component (0.10 +/- 0.01 Hz eq, 5.2 +/- 1.4 mmHg2). On the contrary, in the QP group only the HF component was observed (0.28 +/- 0.03 Hz eq, 3.2 +/- 1.4 mmHg2). The results suggest that 1) in the QP subject the disappearance of the LF component in the SBP variability (i.e., the Mayer waves in humans) is presumably caused by the interruption of the spinal pathways linking supraspinal cardiovascular centers with the peripheral sympathetic outflow and 2) the cervical spinal sympathetic pathways may be instrumental in the genesis of the Mayer waves in humans.

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This study investigated the spontaneous beat-to-beat variabilities in R-R intervals of six traumatic neurologically complete quadriplegic (QP) males and six age-matched healthy males (control) while they were at rest in the supine position in a climatic chamber (temperature 30 degrees C, relative humidity 60%) by means of autoregressive power spectral analysis. As shown by earlier studies, in the control group there were two major spectral components, a high-frequency (HF) component [center frequency 0.30 +/- 0.02 (SE) Hertz equivalent (Hz eq), power 767.5 +/- 384.6 ms2] and a low-frequency (LF) component (0.11 +/- 0.01 Hz eq, 707.5 +/- 198.8 ms2). On the contrary, in the QP group, only the HF component was observed (0.30 +/- 0.02 Hz eq, 421.8 +/- 134.7 ms2). The results suggest that 1) the disappearance of the LF component in the QP subject is presumably caused by the interruption of the spinal pathways linking supraspinal cardiovascular centers with the peripheral sympathetic outflow, and 2) the cervical spinal sympathetic pathways may be instrumental in the genesis of the LF component in humans.

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