Measurement of HRV
STARE, PHYSICAL STRESS
HRV was measured using an SA-3000P (Medicore Co., Ltd. Hanam, Gyeonggi-Do, Korea). Baseline HRV was measured on the morning of the day before surgery in a quiet room in the ward. The patient rested for 5 min before the measurement, and electrocardiogram (EKG) leads were applied. During the measurement, conversation was prohibited, and the patients were asked to open their eyes and stare at an empty wall in a supine position. Subsequent to the baseline measurement, three measurements were performed as follows: T1, 10 min after spinal anesthesia; T2, 10 min after the start of sedative administration; and T3, 20 min after the start of sedative administration. All measurements were conducted by collecting data for at least 3 min and while patients were in a supine position.The collected HRV parameters were calculated automatically by the SA-3000P as follows:
Time domain and complexity parameters.SDNN: standard deviation of the NN intervalRMS-SD: square root of the mean of the sum of the squares of the differences between adjacent NN interval
PSI: physical stress index or pressure indexApEn: approximate entropySRD: successive RR interval difference
Frequency domain parameters.Total powerVLF: very low frequency, 0.003–0.004 HzLF: low frequency, 0.04–0.15 HzHF: high frequency, 0.15–0.4 HzLF Norm (n.u.): Normalized LF = LF / LF + HFHF Norm (n.u.): Normalized HF = LF / LF + HFLF/HF ratio: low frequency / high frequency