分形维数在头低位期问心率变异分析中的应用

目的将分形维数应用于心率变异性分析，分析头低位实验过程中心血管系统的非线性变化趋势。方法对10名被试者进行头低位模拟失重实验，每个人前后做2次，共20组实验数据，记录心电信号并用分形维数进行分析。结果与平卧位相比，头低位15～20min、20～25min、25～30min和恢复期的R-R间期的标准差显著升高；头低位20～25min的相邻R-R间期差值的均方根显著升高；头低位0～5min、5～10min、10～15min、20～25min、25～30min和恢复期的分形维数显著高于平卧位。结论头低位期间心率变异性升高，心血管系统复杂性升高；分形维数应用于心率变异性的分析是可行的。     

近似熵及其在心率变异分析中的应用

目的：介绍近似熵;并将之应用于心率变异分析,分析立位测试过程中心血管系统复杂性的变化。方法：对８名被试者进行立位耐力测试,记录心电信号并用近似熵进行心率变异分析。结果：与立位前平卧位相比,立位０￣５ｍｉｎ、５￣１０ｍｉｎ、１０￣１５ｍｉｎ和１５￣２０ｍｉｎ心脏Ｒ－Ｒ间期显著降低,而立位０￣５ｍｉｎ近似熵显著低于平卧位和立位１５￣２０ｍｉｎ,立位１５￣２０ｍｉｎ近似熵显著低于平卧位,说明立位测试过程中心血管系统复杂性降低,心血管系统的调节模式有改变。结论：近似熵应用于心率变异的分析是可行的。     

分形维数在头低位期间心率变异分析中的应用

目的将分形维数应用于心率变异性分析,分析头低位实验过程中心血管系统的非线性变化趋势。方法对10名被试者进行头低位模拟失重实验,每个人前后做2次,共20组实验数据,记录心电信号并用分形维数进行分析。结果与平卧位相比,头低位15～20min、20～25min、25～30min和恢复期的R R间期的标准差显著升高;头低位20～25min的相邻R R间期差值的均方根显著升高;头低位0～5min、5～10min、10～15min、20～25min、25～30min和恢复期的分形维数显著高于平卧位。结论头低位期间心率变异性升高,心血管系统复杂性升高;分形维数应用于心率变异性的分析是可行的。     

非稳定周期轨道在立位心率变异分析中的应用

目的 研究立位心脏R－R间期信号的非稳定周期轨道的结构，进一步探讨心率变异（HRV）的动力学特征。方法 记录8名受试者平卧位5min和立位20min过程中的心电图，检测HRV信号的非稳定周期轨道。结果 立位时高周期数（周期2和周期3）的非稳定周期轨道出现率降低，HRV吸引子变得相对简单；非稳定周期1轨道位置随着体位和时间的改变而改变1。说明HRV的动力学特征有改变，心血管系统的调节功能有改变。结论：非稳定周期轨道可以刻划HRV的动力学性质，是分析HRV的潜在的方法。     

常规潜艇水下状态对人体24h动态心电图窦性心率和心率变异性的影响

目的 探讨常规潜艇水下状态对人体24h动态心电图实性心率和心率变异性的影响.方法 自2002年3月-2009年7月纳入124名常规潜艇水下航行状态的艇员作为水下组,另选118名陆勤战士作为陆上组(对照组),均为男性.采用12导联动态心电图检查分析系统,对常规潜艇水下状态的艇员进行连续24h动态心电图监测,记录24h平均心率、工作时平均心率及最高心率、睡眠时平均心率和最低心率,并分析水下组与陆上组心率变异性指标的差异.结果 与陆上组相比,水下组睡眠时平均心率及最低心率明显加快(P<0.01),但24h平均心率,工作时最高心率及平均心率均无明显差异.24h心率变异性比较,水下组相邻R-R间期差值的均方根值(rMSSD)、正常相邻R-R间期差值>50ms的百分比(PNN50)较陆上组显著下降(P0.05).而两组24h全部窦性心搏R-R间期标准差(SDNN)、24h每5min时段平均问期标准差(SDANN)、相邻R-R间期之间的标准差(SDSD)、三角函数无明显差异.结论 常规潜艇水下工作状态对艇员睡眠时的心血管自主神经有明显影响.     

防晕船口服液对晕船患者心率变异性的影响

目的观察在海上口服防晕船口服液对晕船高敏者心率变异性的影响。方法在登陆艇上进行双盲对照试验,随机选取10名晕船不敏感者作为对照组,40名晕船高敏者分为安慰组和试验组,分别于开船前半小时服用安慰剂（对照组、安慰组）和防晕船口服液（试验组）,记录受试者4h动态心电图,应用心率变异时域、频域分析方法评价自主神经功能状态,并记录受试者出现的晕船症状。结果防晕船口服液具有良好的预防晕船作用,安慰组抗晕船作用很小,有效率仅20％,而试验组中有7例显效,总有效率达85％,明显优于安慰组（P〈0．01）。安慰组和试验组的时域指标全部窦性心搏R-R间期的标准差（SDNN）、相邻R-R间期差值的均方根值（rMSSD）、相邻RR间期大于50ms占总心动周期数的百分比（PNN50）、每5min时段平均R-R间期的标准差（SDANN）、每5min时段R-R间期标准差的平均值（SDNNindex）和频域指标总功率（TP）、高频功率（HF）均显著高于对照组,其中上述指标在试验组均显著低于安慰组;而极低频功率（VLF）在三组间差异无显著性。结论防晕船口服液具有明显的预防晕船作用,其抗运动病机制可能与降低过高的迷走神经兴奋性有关。     

立位耐力监测系统重复性评价

目的 评价自行设计的立位耐力监测系统的稳定性和重复性。方法 应用自行设计的立位耐力监测系统对28例健康歼击机飞行员进行立位耐力监测,间隔一周时间分别在相同条件下做相同的试验。结果 在两次立位耐力试验中平卧位、立位即刻、1 min、2 min、3 min、4 min、5 min、10 min、15 min和20 min各时间心率、收缩压、舒张压和平均动脉压比较差异均无显著性意义(P>0.05)。结论 自行设计的立位耐力监测系统稳定、可靠。     

心率变异性指标在心血管疾病中的应用

心率变异性（HRV）是指逐次心跳间期之间的微小差异，可评价心脏迷走神经和交感神经活动的紧张性、均衡性及其对心血管活动的影响。指标中PNN50（相邻窦性R-R间期差值〉50ms的百分比），rMSSD（24h的R-R连续差异均方的平方根）和高频与迷走神经活动有关，低频和SDANN（5min窦性R-R间期均值的标准差）主要与交感神经有关。     

体位改变对人体心血管功能的影响（摘要）

目的通过研究人体体位改变时血液动力学、心动时相和心血管调节指标变化,为航天医学研究探索一种能简单、可靠、无创反映人体心血管功能的新方法。方法10g健康男性志愿者,坐位（z）5min,平卧位（P1）10min,头低位（HDT）15。10min,后转平卧位（P2）10min,接着＋75。被动立位（HUT）10min期间,     

运动条件下心率变异的非线性动力学分析

为探讨运动状态时心率变异性的特征，应用非线性动力学的方法分析了安静和运动条件下心率变异的变化，受试者为９名健康男性，实验前安静平卧１０ｍｉｎ后在运动负荷功率５０Ｗ，１００Ｗ各运动１０ｍｉｎ，结果显示，在运动过程中，受试者Ｒ－Ｒ间期平均值，标准差明显减低，同时表征心率变异复杂性的非线性动力学指标（复杂度，熵，关联维，容量维）也明显降低，运动负荷１００Ｗ时受试者的非线性动力学分析指标的下降程度大于其在     

Effect of aerobic training on orthostatic tolerance, circulatory response, and heart rate dynamics.

BACKGROUND: This study was performed to investigate the effects of aerobic training on orthostatic tolerance and to quantify the post-training changes in cardiovascular response and heart rate variability (HRV). METHODS: Tolerance and circulatory responses to two types of lower body negative pressure (LBNP) were examined and compared in a group of healthy male students before and after 6 mo of aerobic training, and the results were further compared with a group of athletes (runners). Changes in HRV associated with training were analyzed by conventional and time-varying autoregressive spectral analysis, as well as by approximate entropy measurement (ApEn)--a statistic quantifying heart rate "complexity" derived from non-linear dynamics. RESULTS: After aerobic training, there was an initial transient hypotension during the supine -50 mmHg LBNP testing and a significant decrease in tolerance to upright graded LBNP in most of the student-subjects. Moreover, after training, there was a significant decrease in ApEn value of the HRV time series during both supine control and LBNP testing, and the rate of cardiac vagal withdrawal and sympathetic activation during the onset of LBNP was faster than that before training. CONCLUSIONS: The present study has provided further evidence that certain types of aerobic training may affect orthostatic tolerance and may be associated with a loss of complexity of HRV during supine resting and orthostatic stress.     

Effects of steady state exercise on the power spectrum of heart rate variability

The effects of steady state exercise on the power spectrum of heart rate variability were studied in 19 healthy subjects. Continuous ECG signals were recorded during 1) 15 min of rest in the supine state, 2) 10 min of standing, 3) 10 min of steady state exercise at 50% of maximum predicted power output on a cycle ergometer, and 4) 15 min of post-exercise recovery in the supine state. Autoregressive modeling was used to determine the power spectrum of heart rate variability. While orthostatic stress produced a significant 51% increase in the ratio of low to high frequency peak spectral power, steady state exercise caused a significant suppression of both low and high frequency components. The low frequency peak power rose to significantly high levels throughout 15 min of the post-exercise recovery period. There was a significant leftward shift in the frequency of the low frequency peak with exercise and a rightward shift during the recovery supine state. These results suggest that neuroregulatory control of heart rate plays a major role in adaptive responses to orthostatic stress and post-exercise recovery, while humoral factors are probably more important in maintaining heart rate during steady state exercise.     

下体负压对抗21d头低位卧床后立位耐力不良的研究

目的观察ＬＢＮＰ对２１ｄＨＤＴ－６°卧床模拟失重所致立位耐力不良的对抗效果。方法１２名健康男性青年志愿者,进行２１ｄＨＤＴ－６°卧床实验。随机分为对照组和下体负压组,每组６人。与对照组不同,下体负压组在最后一周,每天进行１ｈ、－４．０ｋＰａ的下体负压锻炼。结果卧床前,１２名受试者顺利通过７５°、２０ｍｉｎ立位耐力检查。卧床第１０ｄ立位耐力检查时,对照组有５人、ＬＢＮＰ组有４人出现晕厥前或晕厥症状,两组平均耐受时间均低于卧床前（Ｐ＜０．０５）;第２１ｄ时,对照组有５人未通过,平均耐受时间较卧床前显著降低（Ｐ＜０．０５）;而ＬＢＮＰ组有１人未通过,平均耐受时间显著高于对照组（Ｐ＜０．０５）。结论２１ｄ头低位卧床后立位耐力显著降低。下体负压能够有效对抗头低位卧床导致的立位耐力降低。     

Absolute changes in regional cerebral blood flow in association with upright posture in humans: an orthostatic PET study.

To determine whether hemodynamic parameters are changed by upright posture in healthy middle-aged humans, absolute values of regional cerebral blood flow (rCBF) were investigated for three different orthostatic conditions. METHODS: PET with [15O]H2O and arterial blood sampling were performed on eight middle-aged healthy volunteers while they were sitting passively or standing actively. Absolute rCBF values estimated by the autoradiographic method in regions of interest were compared using ANOVA, and relative changes in rCBF were also analyzed voxel by voxel using statistical parametric mapping (SPM). RESULTS: Physiologic data remained unchanged for different conditions. ANOVA and SPM showed that absolute and relative rCBF levels were significantly elevated in the cerebellar vermis in the standing position compared with those in the supine and sitting positions. In contrast, ANOVA showed that rCBF in the frontal and parietal cortices tended to be lower in the sitting and standing positions than in the supine position. Regression analysis showed that the frontal rCBF measured during standing tended to be inversely correlated with age. CONCLUSION: The results showed that cerebellar vermis activation was more marked in the standing position than in the sitting or supine positions, indicating that the vermis is a neural substrate for controlling voluntary upright posture. Brain perfusion in the distal internal carotid artery region may be subject to orthostatic postural changes in healthy middle-aged humans.     

Cardiovascular effects of the breathhold used in determining pulmonary diffusing capacity.

BACKGROUND: The single-breath technique for determination of the diffusion capacity of the lung for CO (DlCO) requires a 10-s breathhold at total lung capacity. The assumption has been that this breathhold does not alter the components of DlCO, i.e., the diffusion capacity of the membrane (Dm) and the pulmonary capillary blood volume (Qc), and therefore measurement of these variables during breathhold represents these variables as they exist during normal breathing. The purpose of this study was to determine the effect of the 10-s breathhold on cardiac output (Q) and Qc while supine and standing. The hypothesis was that the standing posture would have a greater influence on Q and Qc during the breathhold than would the supine posture. METHODS: Twelve male subjects participated. Q, stroke volume (SV), heart rate (HR), BP (MAP), and total peripheral resistance (TPR) were determined before and during the 10-s breathhold determination of DlCO, Qc, and Dm. RESULTS: Results while supine were compared with those while standing. DlCO was reduced on standing, due mainly to a reduction in Qc. SV and Q decreased significantly during the 10-s breathhold in both postures. Both SV and Q decreased more when standing (-53% and -49.5%, respectively) than when supine (-40.5% and -36.5%, respectively). Thus, the 10-s breathhold caused significant reductions in Q and therefore may alter the measurement of DlCO and Qc. CONCLUSIONS: The greater decline in Q during the measurement of DlCO when standing would suggest that the DlCO and Qc values while breathing might be underestimated in the upright posture.     

下体负压作用下心率变异性的线性和非线性动力学分析

为了评估下体负压作用下心率变异性的变化，本文应用了时域，频域分析和复杂度分析了ＨＲＶ。受试者为１５名健康男性。下体负压作用的强度和时间分别为－２．７ｋＰａ，２ｍｉｎ；－４．０ｋＰａ，３ｍｉｎ；－５．３ｋＰａ，５ｍｉｎ；－６．７ｋＰａ，１０ｍｉｎ。     

Blood pressure changes during orthostatic stress: evidence of gender differences in neuroeffector distribution

BACKGROUND: Research has demonstrated that exogenous adrenergic agonists produce dose-related vasoconstriction in men but not women. This suggests that the distribution of adrenergic receptor sites differ with gender. Women may have a higher density of receptor sites in the arterioles (fast acting with low gain) while men may have higher density in the larger vessels (slow acting with high gain). METHODS: To partially test this hypothesis, the time course in beat-to-beat responses in systolic and diastolic BP, and heart rate was compared between six men and six women during the transition from a supine to an upright posture and during prolonged standing. RESULTS: The transient change in systolic and diastolic BP was very rapid in women, but completed within 15 to 30 s after assuming an upright position. Men increased BP at a much slower rate, but continued to produce higher BPs over the complete testing session (up to 15 min). The rate of change for men (15 mm Hg systolic and 10 mm Hg diastolic) was approximately half that for women (30 mm Hg systolic and 15 mm Hg diastolic) during the first 30 s of upright posture. However, after 60 s of standing, absolute change in systolic BP for the men exceeded that of the women by approximately 5 mm Hg for both systolic and diastolic BP. While men's heart rate remained relatively constant during standing, women compensated for the lower change in BP by a continual increase in heart rate throughout the duration of the test. Although both men and women demonstrated increases in norepinephrine at 5 and 15 min during standing, no difference between genders was observed. Similarly, there were no differences in dominant periodicity of heart rate during standing, although women demonstrated slightly higher beat-to-beat variation (RMS) than men. CONCLUSION: The results support the hypothesis of distributional differences in neuroeffector responses between men and women and have implications for how men and women respond to orthostatic stress across a variety of environmental conditions.     

Validity of the polar S810 heart rate monitor to measure R-R intervals at rest

PURPOSE: This study was conducted to compare R-R intervals and the subsequent analysis of heart rate variability (HRV) obtained from the Polar S810 heart rate monitor (HRM) (Polar Electro Oy) with an electrocardiogram (ECG) (Physiotrace, Estaris, Lille, France) during an orthostatic test. METHODS: A total of 18 healthy men (age: 27.1 +/- 1.9 yr; height: 1.82 +/- 0.06 m; mass 77.1 +/- 7.7 kg) performed an active orthostatic test during which R-R intervals were simultaneously recorded with the HRM and the ECG recorder The two signals were synchronized and corrected before a time domain analysis, the fast Fourier transform (FFT) and a Poincaré plot analysis. Bias and limits of agreement (LoA), effect size (ES), and correlation coefficients were calculated. RESULTS: R-R intervals were significantly different in the supine and standing position between the ECG and the HRM uncorrected and corrected signal (P < 0.05, ES = 0.000 and 0.006, respectively). The bias +/- LoA, however, were 0.9 +/- 12 ms. HRV parameters derived from both signals in both positions were not different (P > 0.05) and well correlated (r > 0.97, P < 0.05), except root mean square of difference (RMSSD) and SD1 in standing position (P < 0.05, ES = 0.052 and 0.057; r = 0.99 and 0.98, respectively). CONCLUSION: Narrow LoA, good correlations, and small effect sizes support the validity of the Polar S810 HRM to measure R-R intervals and make the subsequent HRV analysis in supine position. Caution must be taken in standing position for the parameters sensitive to the short-term variability (i.e., RMSSD and SD1).