Evaluation of Autonomic Nervous System Changes Using 2 Short-term Heart Rate Variability During Apnea 3

Background: Frequent cessations of respiration can greatly increase the prevalence 14 rate of arrhythmia. It has been confirmed that cardiac activity is regulated by 15 autonomic nervous system (ANS). And heart rate variability (HRV) is widely used as 16 a method to evaluate the function of ANS. Therefore, we analyzed whether apnea can 17 affect the balance and normal function of ANS using short-term HRV indices. Methods: Forty-five healthy subjects were asked to breathe normally and hold their 19 breathing to simulate 10 times apnea. Thirty-six patients from the dataset of a sleep 20 laboratory for the diagnosis of sleep disorders with 10 times apnea were included in 21 analysis. We calculated short-term HRV indices of subjects in normal respiratory and 22 apneic states, respectively. 23 Results: Compared with normal respiratory state, respiration cease would lead to the 24 values of the mean-RR, nLF, LF/HF, and α1 were significantly increase whereas the 25 values of rMSSD and nHF were significantly decrease. 26 Conclusions: Cessations of respiration would lead to an imbalance in function of 27 ANS, as well as an increase in fractal characteristics of the heart. These changes in 28 physiological state are likely to induce and cause the occurrence of arrhythmia, which 29 is regulated by ANS. 30

hypothesized that HRV could be used to evaluate the effect of apnea on the function 48 of the ANS.

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The results of study1 and study2 show that when apnea (either type) occurred, 51 the values of mean-RR, nLF, LF/HF, and α1 increased and the values of rMSSD and 52 nHF decreased. The HRV indices under different respiratory states in study1 were 53 shown in Table 2

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The HRV indices in different respiratory states in study2 were shown in Table 3 69 and Fig.4. Table 3 and Fig.4 show that for the subjects of study2, comparing with   to an increase in fractal characteristics of the heart. 87 Ⅲ . Discussion

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In this study, the method of short-term HRV was used to measure and evaluate 89 7 the function of ANS in normal respiration and apneic states of two groups of subjects.

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The results showed that compared with the normal respiratory state, simulated apnea interpolate and resample the original signal, so avoids spectral distortion [17]. The reasons for why apnea leads to arrhythmia are multifaceted and complex.

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From an anatomical point of view, it has been found that the inspiratory muscles are 131 relaxed in the lungs when apnea occurs. Then the relaxed muscles cause an increase 132 in intra-thoracic pressure and hinders the venous return to the right atrium, which 133 9 reduces the absolute venous pressure. These low-level changes cause the increase of 134 sympathetic activity through low-pressure baroreceptors, which makes ANS 135 unbalanced and eventually leads to arrhythmia [19]. This study explored the causes of  This study had some limitations. First, although the method of short-term HRV 151 can reflect the changes of ANS during apnea to a certain extent, its accuracy needs to 152 be verified using a more direct method, such as a neural pathways-related approach.

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Second, most of the simulated and actual apnea in our study lasted for only 20 154 seconds. Our study only revealed how these 20-second apneic periods influence ANS.

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The relationship between longer apnea and ANS should be investigated further.

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In this study, we compared short-term HRV indices of subjects in normal We performed two studies to analyze how apnea influences the ANS using HRV  The sampling rate of the ECG and nasal flow pressure signal is 200 Hz.

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Nasal flow pressure was used as the reference signal for dividing normal or  were no significant differences, the index was considered to be available for 225 subsequent analysis.

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The screening results of HRV indices are shown in Table 1. We observed that  we also used R-R intervals of ECG to calculate HRV indices. The R-R intervals were 281 17 determined in the same way as in study1.

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Just like in study1, we calculated and compared the six HRV indices of the 36 283 subjects in normal respiratory (5 minutes) and apneic states (>15 seconds) to evaluate 284 its influence on the balance and normal function of ANS during apnea, respectively.

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In study1 and study2, the analysis and processing of the signals were performed