Minimum Measurement Time Affecting the Reliability of the Heart Rate Variability Analysis

BACKGROUND: Heart rate variability (HRV) test is in widely used for measurement of autonomic nerve system. Although the standard measurement time for short-term HRV analysis is regarded as 5 minutes, it could be varied depending on the clinical situation. Thus, we examined that the valid minimum measurement time for HRV through comparison of HRV among 10 segments per 30 seconds from 30 seconds to 300 seconds. METHODS: The study included 1,457 adult participants who visited the health promotion center in Seoul, Korea from the March 2009 to December 2012. The variables of the time domain and frequency domain analysis of HRV among 10 segments from 30 seconds to 300 seconds were compared using one-way ANOVA test with post-hoc analysis. RESULTS: Compared with 5-minute (300 seconds) HRV, the components of HRV measurement were statistically equal in condition with 180 seconds for standard deviation of all normal-to-normal interval (SDNN), 270 seconds for NN50, 180 seconds for total power, 180 seconds for low frequency power in normalized units (LFn), and 180 seconds for high frequency power in normalized units (HFn), respectively. CONCLUSIONS: Our results suggest that the minimum duration of HRV measurement might be more or than 180 seconds.

Effects of Aerobic Exercise on Heart Rate Variability(HRV)

BACKGROUND: This study was conducted to find out the difference of heart rate variability between practicing Tai Chi and walking at 6 km/hr. METHODS: Twelve healthy volunteers aged 25 to 35 were recruited through advertisement. All the subjects gave their informed consent, and the study was approved by the Institutional Review Board of the Catholic Medical Center Research Foundation. The subjects either practised Tai Chi or walked at 6 km/ hr on a treadmill machine, maintaining 5-minute rest, 20-minute exercise, and 30-minute rest. After 1 week, they switched and performed the other form of exercise. During the exercise, beat-to-beat HRV data was recorded by Polar S-810. We calculated HRV indices using Matlab software program and analyzed the mean value of HRV indices. RESULTS: The differences of the mean value of HRV indices of pre-exercise resting period were not significant. However, repeated ANOVA revealed that there were significant differences of change in the mean of SDNN (-14.27+/-13.03 ms, -33.67+/-20.23 ms; P=0.023), RMSSD (-10.17+/-9.59 ms, -21.90+/-12.60 ms; P=0.087), and STIDX (171.60+/-196.84, 1003.49+/-812.56; P=0.003) between practising Tai Chi and walking. The differences of change in mean heat rate, LF/HF ratio, LF, HF and TP were not significant. The differences of the mean value of HRV indices of the post-exercise resting period were not significant compared to the pre- exercise period. CONCLUSION: The result of this study suggest that exertional intensity of practising Tai Chi is similar to that of walking. Moreover, practising Tai Chi may be more profitable than walking in the aspect of HRV.

The Relationship between Autonomous Function and Fatigue Rating in Patients with Fatigue

BACKGROUND: This study was conducted to find out the relationship between autonomous function and fatigue rating. The subjects were patients with complaints of fatigue who visited the department of family medicine in a general hospital. METHODS: We conducted this study from April to December 2002 in patients complaining of fatigue. The subjects were categorized into low, intermediate, and high fatigue groups. Heart rate variability was measured for five minutes at rest, followed by a five minute mental arithmetic test. We analyzed the relationship between fatigue ratings and autonomous function with SPSS 10.0. RESULTS: There was a statistically significant increase in the mean heart rate variability in the all three groups at rest and with stress. There was a statistically significant increase in LF norm increase in the low and high fatigue groups. HF norm showed a statistically significant decrease in the intermediate and high fatigue group. The variation in LF norms was highest in the low fatigue group and lowest. With the mental arithmetic test, the low fatigue group showed decreased rMSSD, HF and HF norm values compared to the intermediate group. The above values showed decrease in the high fatigue group compared to the low group. CONCLUSIONS: Overactivity of the sympathetic nervous system was observed as fatigue ratings increased. The cadiovascular autonomic response tended to decrease as fatigue ratings increased.

Assessment of Autonomic Function in Stroke Patients by Power Spectral Analysis of Heart Rate Variability

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 0o and 70o 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(p0.05). 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.

Assessment of Autonomic Nervous Function in Young Adults by Power Spectral Analysis of Heart Rate Variability

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: 0 degree. 15 degrees, 30degrees, 45degrees, 70degrees, and 90degrees 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(HFN : 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 HFN than female at tilt table angle 0degree(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.