The powers of the low-frequency(LF) and high-frequency(HF) components characterizing heart rate variability (HRV) appear to reflect, in their reciprocal relationship, changes in the state of the sympatho-vagal balance occurring during orthostatic stress with head-up tilt.

We studied 24 healthy volunteers (median age, 23.1 years) who were subjected after a rest period to a series of passive head-up tilt steps chosen from the following angles: 0⁰. 15⁰, 30⁰, 45⁰, 70⁰, and 90⁰ under the condition of frequency controlled respiration(0.25Hz) in order to get data of the Korean young adults.

During head-up tilt, heart rate and normalized low frequency power(LF_N : 0.05∼0.15 Hz) of HRV showed significant increase(p=0.000), but normalized high frequency power(HF_N : 0.2∼0.3 Hz) and total power showed progressive decrease(p=0.000, p＜0.01 respectively). Male showed significantly higher LF_N and lower HF_N than female at tilt table angle 0⁰(p＜0.01).

Power spectral analysis of HRV appears to be capable of providing a noninvasive quantitatibve evaluation of graded changes in the state of the sympatho-vagal balance.