Effect of posture on heart rate variability in school children.

Heart rate variability (HRV) refers to the beat-to-beat alteration in cardiac cycle length. The objective is to study effect of posture on HRV. Five minutes ECG of children (12 females and 20 males) with mean height 138.88 +/- 11.88 cm, weight 27.66 +/- 5.87 kg and BMI 16.11 +/- 1.38 kg/m(2) were recorded in supine, sitting and standing position. HRV parameters were compared by one-way ANOVA and Bonferroni test. Standing decreases Mean interval between successive RR waves (622.69 +/- 83.24 ms versus 721.66 +/- 89.30 ms versus 750.28 +/- 107.917, p < 0.001), the square root of the mean squared differences of successive interval (25.37 +/- 17.52 ms versus 50.16 +/- 25.03 ms, p < 0.001), numbered of RR interval differences 50ms (40.59 +/- 61.58 versus 115.72 +/- 75.408 versus 134.16 +/- 76.57, p < 0.001), percentage NN50 (9.65 +/- 15.32 versus 29.85 +/- 20.52, versus 36.18 +/- 22.33, p < 0.001), High frequency (HF) peak (152.63 +/- 254.41 versus 427.84 +/- 369.62, 540.84 +/- 452.12, p < 0.05), HF power % (34.91 +/- 17.67 versus 51.99 +/- 17.57 versus 56.94 +/- 17.06, p < 0.001), HF normalised unit (45.05 +/- 17.82 versus 61.11 +/- 17.06 versus 65.73 +/- 15.14, p < 0.001) as compared to sitting and supine. Standing increases low frequency (LF) power % (39.78 +/- 11.76 versus 31.64 +/- 12.33 versus 28.53 +/- 11.65, p < 0.05), LF normalized unit (54.95 +/- 17.82 versus 38.89 +/- 17.05 versus 34.27 +/- 15.14, p < 0.001), LF: HF ratio (1.61 +/- 1.26 versus 0.808 +/- 0.69 versus 0.63351 +/- 0.538, p < 0.001) compared to sitting and supine. This study showed significant decreased in HRV parameters reflecting vagal activity and reciprocal increase in sympathetic activity in standing as compared to sitting and supine. There was no significant change in HRV in sitting as compared to supine.