Comparison between pre-prandial and post-prandial heart rate variability (HRV).

After food ingestion, peptides are released in GIT, which cause local vasodilatation. Therefore, after meals, redistribution of blood occurs because of shifting of large amounts of blood into GIT. In normal individuals, this is well compensated and does not lead to post-prandial hypotension. The mechanism of post-prandial hypotension is well known. We hypothesized that there may be a decrease in parasympathetic activity (tone) after meals to compensate for the change in blood distribution. We carried out the study to find out the changes in the autonomic tone before and after meals (lunch) in normal individuals, using Heart Rate Variability (HRV). From the series of RR intervals marked, the time domain and frequency domain measures of HRV were obtained using Nevrokard software (version 6.4). Continuous ECG was recorded in 15 healthy adult subjects (mean age 29.06 +/- 6.2; 13 males and 2 females). The ECG was recorded in pre-prandial and post-prandial state for a period of five minutes each as follows: (1) just before the subjects had lunch, (2) 15 minutes after lunch, (3) 1 hour after lunch, and (4) 2 hours after lunch. Time domain and frequency domain measures of HRV were compared between pre-prandial state and rest of post-prandial states. The autonomic tone parameters did not show a significant change between the pre-prandial state and the immediate post-prandial state. [Range, i.e., the difference between the maximum and minimum RR intervals (406 +/- 161.14 vs. 416.66 +/- 125), standard-deviation of normal to normal RR interval (56.33 +/- 22.72 vs. 67.63 +/- 26.50), RMSSD (55.02 +/- 35.85 vs. 63.87 +/- 32.60), NN50 (42.13 +/- 29.43 vs. 51.86 +/- 29.83), PNN50 (12.67 +/- 10.29 vs. 15.27 +/- 9.71), HF (49.53 +/- 15.10 vs. 47.07 +/- 16.88), LF (41.41 +/- 13.18 vs. 46.49 +/- 15.99), LF/HF (0.98 +/- 0.53 vs. 1.26 +/- 0.90), total power (148.27 +/- 37.78 vs. 137.61 +/- 37.10)]. No significant change was seen in the above parameters between the pre-prandial state and the later phases of post-prandial state. Since there is no significant decrease in the time domain measures and the HF value between the pre-prandial and the post-prandial states, we conclude that the parasympathetic tone is not altered. The parameters denoting sympathetic tone, ie, LF and LF/HF, also do not show a significant change. This indicates that the cardiovascular autonomic tone is not affected by ingestion of meals in normal individuals. Thus we refute our hypothesis. In conclusion, the HRV parameters do not alter significantly after meals in normal individuals.