The study of cardiac function during anesthesia by phonocardiogram

JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA, VOL. 6, NO. 1, MARCH 2008 Effect of Mixed Anesthesia on Cardiac Function by
Phonocardiogram
Fei Han, Hong-Mei Yan, Xin-Chuan Wei, and Qing Yan Abstract⎯Objective of this investigation is to further
testing are highly consistent and strongly suggestive of analyze the cardiac function status change by phonocar-
changes in myocardial function, and they pointed out that diogram during mixed anesthesia which is conducted by
heart sound changes during stress may be more rapid and midazolam, skelaxin, fentanyi and propofol. The results
sensitive than changes in heart rate and blood pressure [2]. show that blood pressure, heart rate, amplitude of R wave
In recent years, Xiao S. Z. et al. sponsored that and T wave, amplitude of first heart sound (S
phonocardiogram as a noninvasive, high benefit/cost ratio, second heart sound (S
and portable method can be used for the evaluation of cardiac 2) about 37 subjects after anesthesia
decrease compared with baseline, while the ratio of first
performance at the bedside and sports field, and so on [3],[4]. heart sound and second heart sound (S
They even proposed some new indicators to evaluate specific 1/S2) and the ratio
of diastole duration and systole duration (D/S) increase.
cardiovascular status, such as the ratio of S1 amplitude to S2 Our study demonstrates that phonocardiogram as a
amplitude (S1/S2), which can be used to evaluate the noninvasive, high benefit/cost ratio, objective, repeatable
dynamically changing relation between cardiac contractility and portable method can be used for the monitoring and
and peripheral vascular pressure, including up-regulating evaluation of cardiac function status during anesthesia
condition of cardiac contractility during stress; and the ratio of diastolic to systolic duration (D/S), which can be used to evaluate the time of blood flowing to the heart per se during Index Terms⎯Anesthesia, cardiac function, phono-
cardiogram.
Early studies reported that different anesthesia regimens and anesthesia styles had different significant effects on 1. Introduction
cardiovascular function[6]. However, most of these studies were carried out by cardiac catheterization method or In the course of anesthesia and operations, accurate, echocardiography in animals[7]. There is a lack of one effect- reliable, non-invasive and convenient measurement or moni- tive, non-invasive, continuously monitoring and convenient toring of cardiac function is critical for patients, especially method to evaluate the patient's cardiovascular function for heart failure patients. At present, two methods are usually during anesthesia and operations for above described reason. used for cardiac evaluations in clinic. One is cardiac catheter- Studies by Gerard R. et al. showed that heart sound rization method, which is accurate and reliable, but invasive characteristics can be used to monitor cardiac function and not suitable for normal monitoring. The other is echo- during halothane anesthesia in children, and the changes cardiography, which is comparative expensive and inconve- occur rapidly and precede noticeablely in heart rate and blood pressure[8]. In their studies, they didn't assess the Hansen PB's early animal researches showed that there new indicators of cardiovascular status by heart sound and was a very close relationship between the amplitude of the halothane, what they used was a single inhaled anesthetic. first heart sound (S1) and the cardiac contractility and However, a mixed injected anesthesia of midazolam, provided the possibility of phonocardiography as a monitor skelaxin, fentanyi and propofol was another important of cardiac performance during anesthesia [1]. Luisada A. A. anesthetic style often used in clinic. Therefore, the object- et al. suggested that heart sounds should be studied during tive of this investigation was to further analyze the effect anesthesia because the changes that occur during stress of mixed anesthesia on cardiac function status change Manuscript received July 10, 2007; revised October 12, 2007. This work was supported by the National Nature Science Foundation of China under Grant No. 30400105, 973 Project under Grant No. 2003CB716106, and 2. Experiments
Outstanding Youth Fund of China under Grant No. 30525030. 2.1 Experimental
Subjects
F. Han, H.-M. Yan, and Q. Yan are with School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu After approval of the Review Committee of Sichuan 610054 China (Corresponding author's e-mail: hmyan@uestc.edu.cn). University on research involving human subjects and X.-C. Wei is with Department of Anesthesia Medical Center of Huaxi, Sichuan University, Chengdu, 610064, China. informed consent given by every subject was obtained, we JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA, VOL. 6, NO. 1, MARCH 2008 carried out this study in Medical Center of Huaxi, Sichuan 20~40 ms after R waves of ECG and S2 which is primarily University, Chengdu, China. 37 ASA physical status I and II decided by the closure pressure of the arotic and pulmonary patients aged 18 years to 80 years presenting for urologic occurs after the isovolumetric relaxation period during surgery participated in the test. In clinic, midazolam, skelaxin, diastole, before or after the end of T waves[12]. As fentanyi and propofol, being as mixed anesthesia, was used synchronous phase, it is proposed that the coordinate position for patients, which dosages was determined by patients' of R waves is regarded as the beginning of systole duration; weight. Patients with serious cardiac disease or contraindi- the coordinate location of the end of T waves is regarded as cation to mixed anesthesia were excluded. 2.2 Experimental
3. Results
No preoperative medications were given, and all patients had received nothing by mouth for at least 12 hours. In the Characteristic heart sound waveforms before anesthesia operating room, a metallic 3 cm diameter heart sound sensor and after anesthesia are shown in Fig. 2. The amplitude of S1 with a flat frequency response between 35 Hz and 20000 Hz and S2 after anesthesia descends obviously. Fast Fourier (BIOPAC Systems, Inc., USA) was placed at the position of transform tracings for one patient before anesthesia and after maximum S1 assisted by stethoscope; generally, it was anesthesia are illustrated in Fig. 3. Likewise, the amplitude of between the third and fourth rib[9]. The audio signals were spectral edge after anesthesia drops obviously. These results amplified and routed to a notebook PC (sampling rate are agreed with Gerard R's early research [8]. 5000 Hz) and continuously monitored by Biopac MP150 (BIOPAC Systems, Inc., USA) from 2 minutes before anesthesia to 2 minutes after anesthesia. The waveforms were processed with Coifman fourth order wavelet basis to minimize high-frequency noise and the resulting waveforms were processed with Matlab 7.0 [10],[11]. The electrocardiograph (ECG) was monitored synchronously with Biopac MP150; at the same time, blood pressure and pulse oximeter et al. were monitored with anesthesia monitoring instruments (Shenzhen Mindray Bio-medical electronics Co., LTD, China). Fig. 2 Representative heart sound waveforms before anesthesia and Fig. 1. The relationship of PCG and ECG. Two representative audio samples were selected for each patient: baseline (20 seconds), anesthesia duration (20 seconds, after anesthesia had been taking effect). The variance of heart rate, blood pressure, amplitude of R wave Fig. 3. Fast Fourier transform tracings for one patient before and T wave, amplitude of S1 and S2, ratio of S1/S2 and D/S from baseline to anesthesia duraiton were analyzed. The results are presented as Mean ±Std. Thereinto, the systole and Table 1 gives out the comparison of blood pressure, heart diastole duration were located by classical method referred rate and amplitude of R wave and T wave before anesthesia with ECG and PCG. The relationship of PCG and ECG is and after anesthesia. From table 1, the average heart rate of 37 subjects fell from 79±13 bpm before anesthesia to 69±10 bpm closure pressure of the mitral and tricuspid valves occurs at after anesthesia. Similarly, after anesthesia, the average the end of the isometric contraction period during systole, systole and diastole pressure dropped from 127±23 mmHg HAN et al: Effect of Mixed Anesthesia on Cardiac Function by Phonocardiogram and 80±14 mmHg to 84±23 mmHg and 51±14 mmHg, 4. Discussion
As well, the amplitude of patients' ECG descended. As the Mixed injected anesthesia of midazolam, skelaxin, absolute amplitude of ECG may be different for different fentanyi and propofol can restrain the circular system, inhibit patient, we defined the value of R wave and T wave at cardiac muscle, and decrease peripheral vascular resistance pre-anesthesia as 1 for baseline. From Table 1, the average obviously, especially midazolam and propofol[13]. Peripheral relative amplitude of R wave and T wave after anesthesia vascular resistance mainly takes effect on diastole pressure, declined to 0.8978±0.1575 and 0.9411±0.0659, respectively. when it reduced, the pressure of diastole and systole would also reduce, especially pressure of diastole would reduce more Table 1: Comparison of blood pressure, heart rate and amplitude of R obviously. Heart rate influence cardiac cycle directly, if it wave and T wave before anesthesia and after anesthesia slowed down, the duration of diastole and systole would increase, and the pressure of diastole and systole would decrease indirectly, especially the pressure of diastole [14]. After the mixed injected anesthesia took effect, peripheral vascular resistance decreased greatly and heart rate slowed down in a certain extent, which both resulted in the falling of pressure of systole and diastole directly, especially diastole pressure. As a result, blood pressure decreased obviously after * The value of R wave and T wave before anesthesia were defined as Decreased diastole pressure made the driving pressure in The patients' cardiac function indicators at pre-anesthesia closure of the aortic and pulmonary valves decrease, which and post-anesthesia are shown in Table 2. Although previous was primary contributor to S2, ultimately induced the decrease animal experiments and invasive and non-invasive clinical in amplitude of S2. Similarly, decreased systole pressure made trails have shown that there was a very close relationship the driving pressure in the closure of the mitral and tricuspid valves decrease, which was major contributor to S between the amplitude of the first heart sound (S induced the decrease in amplitude of S cardiac contractility, the absolute value of S not be used to evaluate cardiac contractility, as it is affected by some factors, such as the thickness of the chest wall and 1 after anesthesia, thus the ratio of S1 amplitude and S2 amplitude rose. Therefore, S1/S2 can be used to reflect the cardiac function level. Therefore, relative values are usually dynamically changing relation between cardiac contractility adopted. Here, we defined the status of pre-anesthesia as and peripheral pressure during anesthesia. baseline, represented with 1. The values after anesthesia are Likely, the decrease in heart rate made diastole duration relative ones which are the ratio of anesthesia data to and systole duration lengthened, but diastole duration lengthened greater than systole duration, which makes D/S Table 2: Comparison of patients' cardiac function indicators at increased, so D/S can be used to evaluate the time of blood 5. Conclusion
Generally speaking, the decrease of heart rate, the rising of D/S and S1/S2, in a certain extent, are helpful for patients with healthy cardiac condition to get through anesthesia and operation. Whereas, some patients with heart diseases like brachycardiac and arrhythmia, and so on, the changes may be a burden to heart. It needs disposal carefully in clinic. *The value of cardiac function indicators before anesthesia were From above, the results of cardiac indicators by phonocardiogram are consisting with the relative principle of From Table 2, after anesthesia, the average S physiology and pharmacology. Our study demonstrated that amplitude of 37 subjects fell to 0.9258±0.3869 and phonocardiogram as a noninvasive, high benefit/cost ratio, 0.7491±0.3805, respectively; CCCT (the increase of S1 with objective, repeatable and portable method can be used for the monitoring and evaluation of cardiac function status during 1 recorded at baseline) decreased 0.0742 averagely; however, S1/S2 increased to 1.4670±0.7717. Although systolic duration almost unchanged, the diastole duration extended to References
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