KUMJ | VOL. 7 | NO. 3 | ISSUE 27 | JULY-SEPT, 2009

Heart rate variability: Response to graded head up tilt in healthy men
Sharma P, Paudel BH, Singh PN, Limbu P


Abstract:

Background: Heart rate variability is actually a misnomer for R to R variability in cardiac cycle. Variation in successive cycle length is called the heart rate variability (HRV). Head-up tilt is a model of studying cardiovascular haemodynamics, which refl ects in heart rate variability (HRV).
Objectives: To study the effect of 10� and 70� head-up tilt on HRV.
Materials and methods: The study was done in the Department of Physiology using graded head up tilt (passive orthostatism). HRV measurement was done at 10� and 70� tilt and compared with supine using standardised methods on 30 consenting healthy males (age 25.37�3.89 years). The HRV variables across postures were compared by ANOVA and Bonferroni test.
Results: The heart rate increased at 70� compared to 10� and supine (70.48�8.17 Vs 70.22�8.67 and 88.51�12.84 bpm, p<0.001). The 70� tilt decreased vagal HRV indicators compared to 10� and supine: SDNN (31.13�8.12 Vs 38.07�11.29 and 38.13�10.89 ms, p<0.05), RMSSD (20.06 �8.47 Vs 34.23�14.22 and 36.16�12.22 ms, p<0.001), NN50 count (13.03�20.58 Vs 45.07�44.44 and 55.27�44.10, p<0.01), pNN50 (3.28�6.08 Vs 14.06�15.65 and 16.65�14.23, p<0.01), HF power (197.20�143.76 Vs 218.17�155.85 and 216.87�150.98 Hz, p<0.05), HFnu unit (24.28�14.16 Vs 45.48�16.34 and 47.67�19.89, p<0.001). The 70� tilt increased LF power% (197.20�143.76 Vs 218.17�155.85 and 216.87�150.98, p<0.001). LFnu unit (75.72�14.76 Vs 54.52�16.34 and 52.32�19.89, p<0.001), LF: HF (4.96�4.08 Vs 1.53�1.138 and 1.69�1.67, p<0.001) compared to 10� and supine.
Conclusion: At 70� tilt, HRV measures, reflecting vagal contribution to cardiac-cycle length, decreased with reciprocal increase in sympathetic activity compared to 10� or supine leading to increase in sympathetic predominance. A 10� tilt, which is almost equivalent to lying down with pillow, did not change HRV from supine.


Keyword : Cardiac cycle, cardiovascular haemodynamics, head-up-tilt, heart rate variability, sympathetic activity, parasympathetic activity