Bai X; Li J; Zhou L; Li X
Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical
University, Harbin, Heilongjiang, China.
This study was designed to assess
the changes in nonlinear properties of heart rate (HR) variability (HRV) during
the menstrual cycle by means of complexity measures, including sample entropy (SampEn) and correlation dimension (CD), and explore
probable physiological interpretations for them. In 16 healthy women (mean age:
23.8 +/- 2.7 yr), complexity measures along with the spectral components of HRV
(sympathovagal markers) were
analyzed over 1,500 R-R intervals recorded during both the follicular phase
(day 11.9 +/- 1.4) and the luteal phase (day 22.0 +/-
1.4) of each woman's menstrual cycle. Simultaneously, serum ovarian hormone
(estradiol-17 and progesterone) and thyroid-related hormone [free triiodothyronine, free thyroxine
(T(4)), and thyroid-stimulating hormone]
concentrations were measured. With regard to HRV measures, SampEn,
CD, and high-frequency (HF) components decreased from the follicular phase to
the luteal phase, whereas normalized low-frequency
(LF) components and the LF-to-HF ratio as well as resting HR increased. In
regard to hormone levels, whereas progesterone was increased, the other hormone
concentrations were unchanged. Furthermore, across the menstrual cycle, both SampEn and CD were well correlated with the spectral indexes
and free T(4) concentrations, and SampEn
also showed significant correlations with the ratio of estradiol-17 to
progesterone concentrations. These results suggest that the nonlinear
properties in HRV are altered during the regular menstrual cycle and that the
autonomic nervous system, ovarian hormone balance, and free T(4)
may be involved in nonlinear HR control in healthy women. All of these factors
may enrich the physiological meanings of complexity measures.