Translated Abstract
Cardiovascular system plays an important role in maintaining physiological activities of human being. Previous researches show the fact that cardiovascular disease (CVD) has become one of the greatest threats to human health. 90% of sudden cardiac death (SCD) are resulted from malignant arrhythmia, which usually caused by autonomic imbalance. Besides, chronic diseases such as diabetes and essential hypertension have also confirmed to be associated with autonomic imbalance. Other studies declare that emotional trauma and mental stress increase sympathetic efferent, which may lead to instability of myocardial and cerebral regions corresponding autonomic system. Research on the cardiovascular and autonomic function under stress would give us new insights into pathogenesis, diagnosis and treatment of cardiovascular diseases.
This paper is based on the following three issues. First, in order to study dynamic changes of autonomic activity, a new method of HRV assessment should be developed. Second, analysis of cardiovascular function and autonomic nerves responses require the combination of a variety of physiological indexes. Third, influences of different stresses (central stimulation and peripheral stimulation) on cardiovascular and autonomic nerves function should be compared.
Two experiments were designed for activating autonomic nerves system: mental arithmetic test (MAT) and cold pressor test (CPT) corresponding to central activation and peripheral activation. Blood pressure (BP), electrocardiogram (ECG) and Impedence Cardiography (ICG) were collected by Fionmeter MIDI and MP150 continuously for 5 minutes.
Signal denoising and feature points detecting of BP, ECG and ICG were done. Wavelet-based methods were adopted for signal denoising. Wavelet modulus maximum algorithm was used for R-peak extraction. The peak and trough points of blood pressure were detected combined with R-peak results. In order to adapting to the nonlinear and nonstationary physiological signal, Morlet Wavelet Transform was taken for time-frequency analysis of HRV. During the 5 minutes’ experiment, there seems to be a significant difference between 10s~110s (MAT1 and CPT1) and 150s~250s (MAT2 and CPT2) period of the test, so the tests were divided into two parts.
In the whole progress of CPT, peripheral sympathetic nerves were significantly activated while cardiac sympathetic nerves were not. However, peripheral as well as cardiac sympathetic were activated at CPT1 period. At this time, peripheral resistance and heart rate increased, which resulted in the augment of blood pressure. Thus, baroreceptor in carotid sinus and aortic arch, related to parasympathetic activation and sympathetic inhibition, were activated. So the heart beat returned to baseline after a while. Then a regulation mechanism was triggered for maintaining cardiac output by increasing stroke volume when heart rate decreased during CPT2 in order to response to the demand of blood in myocardial and peripheral.
Compared with CPT, there is a more significant difference between the former (MAT1) and latter (MAT2) period of the mental arithmetic test. During MAT1 period, sympathetic nerves haven’t been activated. The increase of HR, BP and CO was generated by self-regulation of the heart. The metabolism of the brain was revved up as the test started. Thus, the revving up leaded to the increase of partial pressure of arterial carbon dioxide (PaCO2). As is confirmed, brain perfusion was highly sensitive to changes in PaCO2. The cerebral and limbs blood flow increased during MAT, which led to the increase of venous return and even high venous pressure. According to the Starling＇s Law of the heart, cardiac output will increase with the gain of venous pressure. The augment of cardiac output (CO) was generated by both SV and HR. Then, the increase of CO led to the increase of systolic blood pressure. The autonomic nerve function started to change after 110s of MAT. Normalized LF (nLF) and LF/HF (PR) increased while HF decreased. The change became stable at 150s, where nLF and PR were significantly higher and HF were slightly lower than baseline. Compared with self-regulation of the cardiac, autonomic nerves activation played a dominant role in the regulation during MAT2 period. As a result, more norepinephrine and epinephrine were released, which resulted in an augment in heart rate, myocardial contractility and peripheral resistance.
Different regulation mechanisms of cardiac and autonomic nerves system were responded to disparate stresses, which lead to diverse cardiovascular risk. A clear understanding of physiological process is the key point of cardiovascular diseases diagnosing and prevention.
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