A study on relationship between heart rate variabilities and autonomic balance during head-up tilt

The power spectral analysis of heart rate variability was performed to evaluate effects of orthostatic stress with head-up tilt on autonomic nervous system for 25 healthy male subjects (age: 24±5 yr.) and a new method was proposed to assess the autonomic balance. The ECG and respiration signals were recorded at tilt angles of 0", 45", 90" and 0" successively for 10 minutes per each stage under the condition of frequency controlled respiration (0.25Hz). Heart rate gradually increased as the angle increased. Similarly, according to the increment of angle, normalized low frequency component (0.05-0.15Hz) gradually increased, whereas normalized high frequency component (0.20-0.30Hz) was reduced. From these results it is speculated that orthostatic stress, head-up tilt, results in the prevalence of sympathetic tone in autonomic balance with the increment of sympathetic tone and the decrement of parasympathetic tone, which seems to mean that autonomic nervous system plays a major role in compensating for disturbances of cardiovascular system due to it.