Experimental analysis of heart rate variability and stress reflex sensitivity in humans

Summary

This experimental method was obtained from the official website of the Fourth Military Medical University

Operation method

Experimental analysis of heart rate variability and stress reflex sensitivity in humans

Principle

The functions of human cardiovascular, gastrointestinal, bronchial, sweat glands and endocrine glands such as pancreas, thyroid and adrenal glands are regulated by autonomic nerves. Many diseases can cause damage and dysfunction of the autonomic nerves, and autonomic nerve damage and dysfunction is one of the causes of many diseases. In the past, a regular heart rhythm was considered to be one of the indicators of a healthy heart, but it is now recognized that an absolutely regular heart rhythm is pathological. Clinical studies have demonstrated that Heart Rate Variability (HRV) is significantly lower in patients with coronary artery disease, angina pectoris, myocardial infarction, sudden cardiac death, congestive heart failure, and uremia than in normal subjects, and that post-infarction arrhythmic events and cardiac mortality correlate significantly with the degree of reduction in HRV.The combination of HRV with cardiac function, late potentials, and electrophysiologic tests can greatly improve the assessment of the immediate and long-term outcome of patients with heart attack. reliability of risk stratification of patients with heart attack in the near and distant future. Baroreflex Sensitivity (BRS) analysis has also been increasingly used in cardiovascular disease research over the past decade. The pressure reflex system is an important part of the regulation of the cardiovascular system, in which the vagus and sympathetic nerves are particularly important for the heart and blood vessels. Pressure receptors are mainly found in the carotid sinus and the aortic arch. Stimulation of pressure receptors when pressure is high increases parasympathetic tone and decreases sympathetic tone, which in turn leads to a decrease in heart rate, cardiac index, and vasodilatation, and ultimately decreases blood pressure to the normal range. The effectiveness of this adjustment pathway, i.e., pressure reflex sensitivity, can be understood by changes in heart rate. Although both components of the autonomic nervous system influence heart rate, pressure reflex sensitivity primarily reflects parasympathetic reflexes. By extracting the electrocardiographic RRI (R-wave interval, R-R Interval) and the corresponding arterial blood pressure (systolic, diastolic, or mean) for a certain period of time and analyzing the RRI and BP digital sequences in time and frequency domains, one can find their mean square deviation (TV), standard deviation (SD), power spectral density (PSD), low-frequency component (LF), high-frequency component (HF), the ratio of high and low frequencies ( LF/HF), as well as parameters such as their correlation function (Coherence) and pressure reflection sensitivity (BRS). For power spectral analysis, there is a consensus that the high-frequency component of the power spectral density curve around 0.25 Hz (about 4 heartbeats a cycle) is related to the parasympathetic nerves (mainly related to respiratory movements), while the low-frequency component around 0.1 Hz (about 10 heartbeats a cycle) is related to both the sympathetic and parasympathetic nerves. Recently, Lumbardi et al. observed in animal experiments that cardiac sympathetic nerves have the same transmitter variants as LF, and concluded that LF is mainly related to sympathetic activity.LF/HF reflects the balance of sympathetic and vagal regulation, which is reduced in normal subjects during quiet and increased during stress.HRV and BRS analyses provide a nontraumatic means of examining autonomic regulation and central integration functions. HRV and BRS analysis provides a non-invasive method for checking the autonomic regulation and central integration function, which can be used to check the degree of autonomic nerve damage in patients with coronary heart disease, diabetes mellitus, renal failure and other diseases, as well as for judging the degree of fatigue and aging, which is of great use for professional selection and geriatrics prevention and treatment. I. HRV and BRS Analysis Methods The detection methods of R-R interval (RRI) and arterial systolic blood pressure (SBP) are shown in Fig. 22-11. The program automatically detects the intervals according to the rate of change of the ECG signals and the time course, and detects the maximum value of systolic blood pressure in each cardiac cycle, thus obtaining the corresponding RRI and SBP digital sequences. Commonly used analyzing methods and main parameters 1. time-domain analysis (TDA) (1) Simple measurement method. The difference between the longest RRI and the shortest RRI is used as an index of HRV. For example, it is used in the study of fetal heart rate. (2) Variance and standard deviation (SD) of RRIs. RRI data are typically 256 or 512, and can be up to 24 hours long. In normal subjects, the 24-hour SD is usually >50 ms. (3) Coefficient of variation (CV) of SD. CV can exclude differences in intrinsic heart rate of the subjects and increase the comparability. (4) R-R interval jump index (RRI) The difference between neighboring RRIs is determined, and the frequency of RRIs exceeding a predetermined value (generally 50ms) is calculated hourly and plotted on a curve, with fluctuations in the curve representing vagal activity. (5) HRV index The total number of RRIs/the number of RRIs with the largest proportion in a certain period of time. The number of RRIs in a certain period of time/the number of RRIs with the largest proportion is usually greater than 25 in normal people. 2. frequency-domain analysis (FDA) adopts the Fast Fourier Transform (FFT) or Autoregressive (AR) model, and finds out the Power Spectral Density (PSD), followed by the Power Spectral Density (PSD), which is the average of the power of the RRIs in a normal person. Density (PSD), and then calculate the absolute value and normalized unit of each frequency component. The autoregressive model (AR) has a higher resolution than the FFT algorithm, and there are recursive algorithms such as Burg, Marple, etc. The autoregressive model is used to calculate the power spectral density (PSD), and then calculate the absolute value and normalized unit of each frequency component. (1) Amplitude unit of power spectral density The unit of power spectral density is ms2/(Cycle/Beat, c/b) or ms2/Hz. Its Normalized Unit (NU) is obtained according to the following formula: LF (NU) = LF (absolute value) / ( PSD curve total area - DC ) × 100HF (NU) = HF (absolute value) / ( PSD curve total area - DC ) × 100 where DC is the DC component of the spectrum. (2) Frequency Unit of Power Spectral Density The frequency unit of power spectral density is Cycle/Beat, which can be converted to Hz (times/second) using the following formula: F (Hz) = 1000 × F (Cycle/Beat) / PPImean (the mean value of the RRI).(3) Classification of LF and HF: Lower Frequency (0.03 to 0.1 Cycle/Beat), Medium Frequency (0.1 to 0.2 Cycle/Beat), Medium Frequency (0.1 to 0.1 Cycle/Beat), Medium Frequency (0.03 to 0.1 Cycle/Beat). (0.1 to 0.2 Cycle/Beat), HF (around 0.25 Cycle/Beat, depending on respiratory rate). 3. Other Observation Methods (1) Histograms Find TV, 10% TV, 50% TV, etc. (2) Phase plane diagram (trajectory diagram). Figure 22-12 shows the analyzed graphs of RRI and HRV. III. Findings of the Survey of Normal Values of TV and LF/HF at Quiet in Healthy Individuals It has been found that the HRV parameters at quiet in healthy individuals from early childhood to their 30s show a slow change with age, and that the HRV parameters at quiet in healthy individuals after the age of 40 also show a slow change with age.

Materials and Instruments

Human body
Biosignal processing system "HRV and BRS analysis" software

Move

1. Turn on the biosignal processing system with the ECG leadwire connected to the first channel and the pulse transducer connected to the second channel.

2. The subject was placed in a supine position, the skin was cleaned at the contact point of the ECG electrode plate, the ground end of the lead wire was connected to the right lower limb of the subject, and the two recording ends were connected to the left upper limb and the right upper limb respectively. The pulse transducer was placed at the radial artery pulsation, and the harness was fixed and adjusted for tightness.

3. Run the "HRV and BRS analysis" software and observe the ECG and pulse waveforms in the sampling interface. Set the amplifier time constant and high-frequency filter, and adjust the amplifier gain according to the waveform size. If there is little difference in amplitude between the R wave and other wave groups, change the ECG leads.

The amplifier parameters are set as follows:

Time constant: ECG 2s ~ 0.2s, pulse DC ~ 2s.

High-frequency filtering: take 300～500Hz for both ECG and pulse.

Gain: 1000～5000 times for ECG and 100～400 times for pulse.

4. The subject rests quietly for 10-20 minutes, keeps the breathing steady, and cannot sleep with eyes closed. Measure the subject's blood pressure with a mercury sphygmomanometer, call the "calibration" function of the program, and enter the measured systolic and diastolic blood pressure into the calibration dialog box, so as to calibrate the amplitude of the pulse wave.

5. Record a signal, the signal length is generally 256 ~ 4096 cardiac cycles, according to the experimental needs of setting.

6. After a short break, the subject is asked to do mental arithmetic or is given a cold stimulus (finger immersed in cold water), and then a signal is recorded.

7. Analyze HRV and BRS

Caveat

1. No sedative drugs should be taken several hours before the measurement, and no excitatory beverages should be consumed within 1 hour before the measurement.

2. If cold water immersion of the finger is used as a stimulation method, the temperature of the cold water should be controlled at about 4℃.

3. During the test, the subject should remain relaxed to avoid myoelectric interference; the wrist on which the pulse transducer is placed should be kept stable to prevent pressure errors due to changes in binding force.

4. The testing environment should be kept quiet and the room temperature should be around 25℃.

For more product details, please visit Aladdin Scientific website.

https://www.aladdinsci.com/