Objective: To evaluate the effects of orthostatic stress with a head-up tilt on the autonomic nervous system and to determine how a cerebral stroke influences the cardiac autonomic function, using the power spectral analysis(PSA) of heart rate variability(HRV).

Method: We studied 11 stroke patients with a left hemiplegia and 14 patients with a right hemiplegia. Their hemispheric brain lesions were confirmed by the MRI. The ECG and respiration signals were recorded at the tilt angle of 0^o and 70^o for 5 minutes under the condition of frequency controlled respirtaion(0.25 Hz). Data were compared with the age- and sex-matched 12 healthy controls.

Result: In a control group, the normalized high frequency power showed a significant decrease during the head-up tilt(p＜0.05), whereas the normalized low frequency power showed a significant increase(p＜0.05). But for the left and right hemiplegia groups, there were no significant changes of normalized high and low frequency power under the orthostatic stress(p＞0.05). Compared with the right hemiplegia and control groups, the left hemiplegia group was associated more with a reduced low and high frequency power and showed no significant changes under the orthostatic stress.

Conclusion: PSA of HRV can identify the reduced cardiac autonomic activity in stroke patients, with a greater reduction in the left hemiplegia group than in the right hemiplegia group, which may cause a high risk of cardiac arrhythmias and sudden death.

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.