Using the Standard-Load HRV Method to Verify the Health-Preserving Effect
Heart Rate Variability (HRV) means the minute variability between heart beat cycles. It is reflected by the irregular variations in length of each cardiac cycle. Today HRV analysis is widely used in clinical treatment. It is an effective indirect method to evaluate the functions of the autonomic nerves with non-invasive and quantitative features [1][2].
　　Clinical HRV tests are mostly conducted when the patients lie still. But researches have revealed that HRV of patients having autonomic nerve dysfunction may be normal when they lie still but become abnormal in some stress situations (deep breaths, mental arithmetic activities, or movements). Therefore, in this study we first improved the method for routine HRV test, established a standard-load HRV test scheme, and used this scheme to evaluate the effects of Health Qigong•Ba Duan Jin on the autonomic nerve functions of the old and middle-aged people in order to verify the health-preserving value of Health Qigong•Ba Duan Jin and to lay a foundation for its promotion and popularization in the nationwide fitness campaign.
　　1. Objects and methodology
　　1.1 Objects
　　Experimental group: 30 old and middle-aged women (56~60 years of age) having practiced Health Qigong•Ba Duan Jin for 6 years in Fengtai District, Beijing; all objects were basically health; patients with diabetes, cardiovascular diseases, and high blood pressure were eliminated.
　　Control group: 30 old and middle-aged women (56~60 years of age) having no habit of in Fengtai District, Beijing; all objects were basically health; patients with diabetes, cardiovascular diseases, and high blood pressure were eliminated. See Table 1 for the basic information about the test objects.
　　Table 1. Basic Information about Test Objects
　　Group nAge (year)Height (cm)Body weight (kg)
　　Control group 3057.29±1.8157.7±5.367.8±7.2
　　Experimental group 3057.14±1.3156.5±4.966.6±7.5
　　1.2 HRV experiment
　　(1) Standard-load experiment scheme
　　Samples were taken from all test objects from 8:00 to 11:00 AM. The entire sampling process consisted of 7 consecutive stages which were, in chronological order, meditation, sit-stand movements (20 times/min), meditation, deep breaths (12 times/min), meditation, sit-stand movements (20 times/min), and meditation. Each stage lasted 5 minutes. It took 35 minutes to complete the entire process.
　　The entire experiment was divided into 3 stages: The first 5-minuted meditation was the pre-load period. The time from the first sit-stand movement to the second sit-stand movement was the standard-load period. The last 5-minute rest was the post-load period (See Fig. 1).
　　Figure 1. Schematic View of the Standard-Load HRV Experimental Plan
　　(2) Requirements on all test stages
　　Sit-stand movement: The test object naturally stands in front of a chair with her back towards the chair and with her arms naturally overlapped as a preparative pose. After hearing a command, the test object starts to do sitting-down and standing-up movements with the rhythm of a metronome. The test object will respectively complete 20 sitting-down movements and 20 standing-up movements within 1 minute for 5 consecutive minutes. After the experiment, the test object immediately sits in the chair for a rest. The chair is as high as the knees. The purpose of the sit-stand movement is to activate the sympathetic nerves.
　　Deep breath: Naturally relax and sit in a chair. Take breaths according to an orally-given rhythm. Take 12 inhalations and 12 exhalations respectively. The breaths shall be even and natural. The purpose of the deep breath is to activate the sympathetic parasympathetic nerves.
　　Rest: Naturally relax and sit in the chair. Close eyes and rest the mind. The external environment is gentle music without any noise.
　　(3) Instruments
　　A Holter monitor and matching HRV analysis software developed by No.4 Research Institute, PLA Air Force.
　　(4) Data processing
　　The continuously-recorded 35-min electrocardiosignals were input into a computer and all ectopic beats (arterial beats, nodal beats, ventricular beats, escape beats, and tachycardia) and artifacts were deleted through human-machine dialog. Sinus beats were analyzed and intervals between neighboring RR were calculated to obtain the time-domain parameters of HRV: SDNN, CV, and RMSSD. Then Fast Fourier Transform (FFT) was used to derive HRV power spectrum parameters: TF, VLF, LF, NLF, HF, NHF, and LF/HF. See Table 2 for the definitions of all time-domain and frequency-domain parameters.
　　Table 2. Indicators Commonly Used for HRV Analysis
　　MethodCommonly-used indicatorsEntityDefinition
　　Time domainSDNNmsStandard deviation of all normal RR intervals
　　RMSSDmsRoot mean square deviation of neighboring RR intervals
　　CV%RR interval variability coefficient
　　Frequency domainTFms2Total power: total area from 0.0 - 0.4Hz
　　VLFms2Ultra LF power: area of 0.0 - 0.04Hz frequency band
　　LFms2LF power: area of 0.04 - 0.15Hz frequency band
　　HFms2HF power: area of 0.15 - 0.4Hz frequency band
　　LF/HFNoneRatio between LF power and HF power:
　　NLFNoneNormalized LF power: NLF = [ LF/ (TF-VLF)]×100%
　　NHFNoneNormalized HF power: NHF = [ HF/ (TF-VLF)]×100%
　　1.3 Statistical analysis
　　All data is expressed by mean value ±( ). T-test is used for comparison between groups. Since all indicators have a non-normal distribution in frequency-domain analysis, they have to be put to logarithmic transformation before t-test.
　　2. Result:
　　2.1 Analysis results of HRV throughout the entire test process
　　Table 3. Time-Domain Analysis Results of HRV throughout the Entire Test Process
　　Group nRRmean(ms)SDNN(ms)CV(%)SDmeanSDSDRMSSD(ms)
　　Control group 30732.7±92.551.9±15.67.2±1.969.1±23.922.1±8.614.7±5.5
　　Experimental group 30744.6±98.2*54.5±25.57.2±2.768.4±29.123.1±14.716.4±7.8
　　Notes: *, P
　　Table 4. Frequency-Domain Analysis Results of HRV throughout the Entire Test Process
　　Group nVLF (ms2)LF (ms2)HF (ms2)TF (ms2)NLF (nu)NHF (nu)LF/HF
　　Control group 305225±2502348±262133±1055707±375371.5±12.927.5±12.93.3±2.2
　　Experimental group 305697±2445421±229126±1016245±360770.5±14.328.5±14.33.4±2.5
　　2.2 Analysis results of HRV in various stages
　　(1) Time domain analysis results
　　Table 5. Time-Domain Analysis Results of HRV before Standard Load
　　Control group (n = 30)Experimental group (n = 30)
　　RRmean (ms) 793.0±77.6838.6±87.3**
　　SDNN (ms) 86.1±23.5 100.4±24.7**
　　RMSSD (ms)16.4±7.219.3±5.5
　　CV (%)15.6±6.717.1±7.6
　　Table 6. Time-Domain Analysis Results of HRV during Standard Load
　　Control group (n = 30) Experimental group (n = 30)
　　RRmean (ms) 645.4±36.7 657.9±68.5
　　SDNN (ms) 103.9±22.4 125.3±26.1*
　　RMSSD (ms)15.0±9.816.8±7.3
　　CV (%)12.7±3.5 14.5±2.8*
　　Table 7. Time-Domain Analysis Results of HRV after Standard Load
　　Control group (n = 30)Experimental group (n = 30)
　　RRmean (ms)741.1±42.6765.5±54.4
　　SDNN (ms)94.6±32.3120.4±34.6*
　　RMSSD (ms)16.3±9.718.8±7.1
　　CV (%)18.8±6.722.1±7.6*
　　(2) Frequency domain analysis results
　　Table 8. Frequency-Domain Analysis Results of HRV before Standard Load
　　Control group (n = 30)Experimental group (n = 30)
　　TF (ms2)264.6±89.6316.4±123.9
　　LF (ms2)21.5±12.819.2±7.4**
　　HF (ms2)6.5±4.67.7±4.9
　　LF/HF5.4±2.23.8±2.1*
　　NLF (nu)73.1±8.355.0±9.0**
　　NHF(nu)26.9±6.245.0±11.0**
　　Table 9. Frequency-Domain Analysis Results of HRV during Standard Load
　　Control group (n = 30)Experimental group (n = 30)
　　TF (ms2)343.0±148.7378.6±165.6
　　LF (ms2)50.0±30.345.5±27.3
　　HF (ms2)9.0±4.512.4±4.9*
　　LF/HF7.7±5.26.7±4.3
　　NLF (nu)80.7±12.170.1±13.1
　　NHF(nu)19.5±10.429.8±15.3**
　　Table 10. Frequency-Domain Analysis Results of HRV after Standard Load
　　Control group (n = 30)Experimental group (n = 30)
　　TF (ms2)294.9±136.9346.3±144.2
　　LF (ms2)36.3±11.527.3±11.2
　　HF (ms2)6.2±5.49.0±9.2
　　LF/HF6.2±2.44.8±3.1
　　NLF (nu)77.2±14.362.3±12.7â–²
　　NHF(nu)23.2±11.137.5±12.3â–²
　　3. Discussion
　　HRV analysis is a non-invasive clinical method currently used for the quantitative analysis of the autonomic nerve functions. Researches have proved that: the strengthened activity of sympathetic nerves and (or) weakened activity of pneumogastric nerves may cause cardiac electrophysiological instability and reduce the threshold of ventricular fibrillation. And the strengthened activity of pneumogastric nerves and (or) reduced activity of sympathetic nerves will raise the threshold of ventricular fibrillation and protect the heart [3]. The reduced activity of pneumogastric nerves and (or) strengthened activity of sympathetic nerves will both reduce HRV [4]. A lot of researches have proved that the reduced HRV is a very significant indicator of death risk caused by acute myocardial infarction [5]. Therefore HRV analysis can provide information about the changes in the tension of pneumogastric and sympathetic nerves and about the risk of sudden cardiac death. HRV analysis involves the time-domain method, frequency-domain method, and non-linear analytical method. The time-domain method is simply and can properly reflect the activities of the pneumogastric nerves. The frequency-domain analytical method can separate the activities of the sympathetic nerves from those of the pneumogastric nerves. The non-linear analytical method is quite complicated and its clinical application is still immature. The HF indicator in frequency domain analysis is a reliable one that reflects the activities of the cardiac pneumogastric nerves. LF is mediated by both the sympathetic nerves and pneumogastric nerves. LF/HF are sensitive indicators that reflect the changes in the tension balance between the sympathetic nerves and pneumogastric nerves [2].
　　In this study, both the time-domain and frequency-domain method were used for a comparative analysis of HRV between old and middle-aged people who had been practicing Health Qigong•Ba Duan Jin for a long time and old and middle-aged people who seldom took part in any physical exercise. Among the time-domain indicators, the RMSSD, SDNN, and CV of old and middle-aged objects in the experimental group were all higher than those of the objects lacking physical exercise, especially during the standard load and during the recovery stage after the load (P
　　On the other hand, this research has also revealed that the heart rate of healthy old and middle-aged people who regularly take Health Qigong•Ba Duan Jin exercise is significantly lower than that of old and middle-aged people who lack physical exercise (P
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　　[3] Dougles P, Zipes DP. Influence of myocardial ischemia and infarction on autonomic infarction of heart[J]. Circulation, 1990, 82: 1095-1105.
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