ABSTRACT

Background: Heart rate variability (HRV) is a non-invasive recording of the sympathovagal interaction modulating cardiovascular function. Analysis of HRV has been used to evaluate cardiac autonomic tone. There are different autonomic tones at different times of the day infl uenced by daily activities, stress, and environment. The study was done to observe the effect of time of day on sympathovagal balance in healthy young adults using frequency domain indices of HRV.
Aim and Objective: The aim was to fi nd out the ultradian rhythm variation (morning and evening) in frequency domain indices of HRV in healthy young adults.
Materials and Methods: A total of 100 healthy subjects (50 males and 50 females) in the age group of 18-25 years were included in the study. They were screened by history and physical examination to exclude cardiovascular and any abnormalities.
Methodology: Short term HRV (Lead II electrocardiography [ECG] for 5 min) was done by using standardized neuroperfect electromyography 2000 (with installed HRV software) machine. For each and every subject two recordings were done, – one in the morning between 9 and 10 AM before starting the daily activities of the day and one in the evening between 3 and 4 PM at the end of the day.
Result: The results were statistically analyzed by using Students t-test. Comparison of frequency domains low frequency (LF), high frequency (HF), LF/HF ratio between morning and evening sessions for the same individual were carried out. LF was increased in the evening session when compared to the morning session and the difference is statistically signifi cant (P < 0.0001). HF was decreased in the evening session when compared to the morning session and the difference is not statistically signifi cant (P = 0.2745). LF/HF ratio also increased in the evening session when compared to the morning session and the difference is statistically signifi cant (P < 0.0001).
Conclusion: There exists a signifi cant difference in LF and LF/HF ratio between morning and evening recordings. It is concluded that time of the day has a signifi cant impact on cardiac autonomic tone.