Abstract
Background: The menstrual cycle signifies a fine balance of female sexual hormones and integrity of hypothalamohypophyseal-gonadal axis, during reproductive age. Many women experience unpredictable menstruation when they encounter various kinds of stress situations that often interrupt the normal cycle. Heart rate variability is the quantitative measure of autonomic tone.

Aims and Objectives: The present study is aimed to observe the effect of stress and autonomic balance in different menstrual cycle phases of young adolescent female medical students.

Materials and Methods: It is a cross-sectional study where 50 young medical female students aged between 18 and 25 years were recruited and their demographic features were measured. All the study procedures except cortisol collection (early morning) were done in between 9 AM and 11 PM after 1–2 h of light breakfast.

Results: All parameters were measured in premenstrual phase (25th ± 4 days) and postmenstrual phase (10th ± 5 days). Low frequency (LF) increases from 0.07 ± 0.009Hz to 0.08 ± 0.005 Hz (P – 0.01). However, high frequency decreases from 0.27 ± 0.02Hz to 0.26 ± 0.01Hz (P - 0.01). The time domain parameters SDNN 59.11 ± 24.1 increase to 74.34 ± 52.7 (P – 0.04). STD HR significantly reduced from 69.58 ± 12.1 to 35.36 ± 16.4 (P - 0.01). RMSSD increased from 47.98 ± 5.5 to 75.24 ± 14.6 (P – 0.02). However, NN50 reduced from 64.65 ± 12.8 to 48.52 ± 12.4 statistically significant (P – 0.05). However, there is no significant change in cortisol levels in both phases.

Conclusion: The results suggest that there is a significant difference in sympathovagal balance between pre- and post-menstrual phases. LF indicates that vagal discharge is more in premenstrual phase, whereas sympathetic tone increases in postmenstrual phase.

Key words: Heart rate variability; Sympathovagal balance; Menstrual cycle; Stress; Low frequency; High frequency