有氧锻炼引起的心率动力学变化的近似熵分析

为研究有氧锻炼对心率动力学的影响，采用近似熵（ＡｐＥｎ，ａｐｐｒｏｘｉｍａｔｅｅｎｔｒｏｐｙ）方法对大学生有氧锻炼前、后及中长跑运动员的心率变异性（ＨＲＶ）信号进行了分析，并与相同条件下的时域分析及谱分析结果进行了比较。结果表明：６个月有氧锻炼引起大学生心率动力学一定改变，锻炼后在仰卧状态及ＬＢＮＰ作用下，其ＲＲ间期序列的ＡｐＥｎ值均较锻炼前显著降低（Ｐ＜０．０１，Ｐ＜０．０５）。中长跑运动员组在仰卧状态及ＬＢＮＰ作用初期，ＲＲ间期序列的ＡｐＥｎ值亦均显著低于大学生组有氧锻炼前的各相应值（Ｐ＜０．０１，Ｐ＜０．０５）。大学生组在－６．６７ｋＰａ／３０ｍｉｎＬＢＮＰ作用期间，ＨＲＶ信号的ＡｐＥｎ值均随作用时间呈线性持续降低变化（Ｐ＜０．０１）。但常规的时域及频域分析却不能区分出上述这些差别。结果提示：有氧锻炼可使ＨＲＶ信号的复杂度降低，而且在ＬＢＮＰ作用期间心率调节的同步化过程是持续进行的。     

重力应激下非平稳心率变异性的时变自回归谱分析方法

为分析重力应激下非平稳心率变异性信号，建立了时变自回归模型谱估计方法，藉此可得到各项谱指标随时间变化的曲线，以动态地观察，研究不同重力应激作用下心脏自主神经调节的过程，曾利用该方法处理８名被试者有氧锻炼前、后坐位下体负压高频谱成分逐步降低，以及低、高频谱成分比值（ＬＦ／ＨＦ）逐步升高直至稳定水平的过程；前者反映心迷走撤除，后者反应心交感激活的动态过程。还可以观察到有氧锻炼６个月后ＨＦｎ、ＬＦｎ变化     

复杂度在立位期间心率变异分析中的应用

目的 介绍非线性指标复杂度,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。记录心电信号并用复杂度进行心率变异分析。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,R-R间期标准差和相临R-R间期差值的标准差（RMSSD）显著降低。立位0-5min,15-20min复杂度和近似熵显著低于平卧位。结论 立位期间心率变异降低。心血管系统复杂性降低。复杂度应用于心率变异的分析是可行的。     

Lower-body negative-pressure exercise and bed-rest-mediated orthostatic intolerance

PURPOSE: Supine, moderate exercise is ineffective in maintaining orthostatic tolerance after bed rest (BR). Our purpose was to test the hypothesis that adding an orthostatic stress during exercise would maintain orthostatic function after BR. METHODS: Seven healthy men completed duplicate 15-d 6 degrees head-down tilt BR using a crossover design. During one BR, subjects did not exercise (CON). During another BR, subjects exercised for 40 min.d(-1) on a supine treadmill against 50-60 mm Hg LBNP (EX). Exercise training consisted of an interval exercise protocol of 2- to 3-min intervals alternating between 41 and 65% (.)VO(2max). Before and after BR, an LBNP tolerance test was performed in which the LBNP chamber was decompressed in 10-mm Hg stages every 3 min until presyncope. RESULTS: LBNP tolerance, as assessed by the cumulative stress index (CSI) decreased after BR in both the CON (830 +/- 144, pre-BR vs 524 +/- 56 mm Hg.min, post-BR) and the EX (949 +/- 118 pre-BR vs 560 +/- 44 mm Hg.min, post-BR) conditions. However, subtolerance (0 to -50 mm Hg LBNP) heart rates were lower and systolic blood pressures were better maintained after BR in the EX condition compared with CON. CONCLUSION: Moderate exercise performed against LBNP simulating an upright 1-g environment failed to protect orthostatic tolerance after 15 d of BR.     

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。     

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。     

Aerobic fitness does not contribute to prediction of orthostatic intolerance

Several investigations have suggested that orthostatic tolerance may be inversely related to aerobic fitness (VO2max). To test this hypothesis, 18 males (age 29 to 51 yr) underwent both treadmill VO2max determination and graded lower body negative pressures (LBNP) exposure to tolerance. VO2max was measured during the last minute of a Bruce treadmill protocol. LBNP was terminated based on pre-syncopal symptoms, and LBNP tolerance (peak LBNP) was expressed as the cumulative product of LBNP and time (torr-min). Changes in heart rate, stroke volume, cardiac output, blood pressure, and impedance rheographic indices of mid-thigh-leg fluid accumulation were measured at rest and during the final minute of LBNP. For all 18 subjects, mean (+/- SE) fluid accumulation index and leg venous compliance index at peak LBNP were 139 +/- 22 ml and 3.9 +/- 0.4 ml . 100 ml . torr-min-2 x 10(3), respectively. Pearson product-moment correlations and step-wise linear regression were used to investigate relationships with peak LBNP. Variables associated with endurance training, such as VO2max and percent body fat, were not found to correlate significantly (P less than 0.05) with peak LBNP and did not add sufficiently to the prediction of peak LBNP to be included in the step-wise regression model. The step-wise regression model included only fluid accumulation index, leg venous compliance index, and blood volume, and resulted in a squared multiple correlation coefficient of 0.978. These data do not support the hypothesis that orthostatic tolerance as measured by LBNP is lower in individuals with high aerobic fitness.     

血容量减少对立位应激反应影响的仿真研究

目的 研究不同程度的血容量减少对心血管系统立位应激反应的影响,探讨血容量降低在航天失重后心血管失调和立位耐力降低机理中的意义。方法 在仿真下体负压（LBNP）暴露时心血管系统反应模型的血液重新分配子模型中引入血容量减少因素,仿真血容量减少0－25％后LBNP时心率（HR）和血压BP变化,结果 血容量减少低于总血量的5％条件下,心血管系统可以通过压力反射调节作用维持LBNP时政党的HR和BP;血容量减少超过约15％,在安静仰卧位时,HR和BP正常,但LBNP时BP迅速降低,系统可失去稳定性。结论 血容量减少将导致心血管系统对立位应激反应的改变。     

Altitude, heart rate variability and aerobic capacities

We analyzed the relationship between aerobic capacities and changes in heart rate variability (HRV) in Nordic-skiers during living high-training low (Hi-Lo). Eleven skiers trained for 18 days at 1200 m, sleeping at 1200 m (LL, n = 5) or in hypoxic rooms (HL, n = 6, 3 x 6 days at altitudes of 2500 - 3000 - 3500 m, 11 h . day (-1)). Measurements were performed before, during and two weeks after Hi-Lo. VO(2max), peak power output were not improved in HL nor in LL, whereas VO(2) and power at the respiratory compensation point (VO(2RCP) and PRCP) increased by 7.5 % and 5.0 % only in HL. Significant changes in HRV occurred only in LL, in the standing position, including a 30 % (p < 0.05) increase in resting heart rate (HR), a 50 % (p < 0.05) decrease in total spectral power (TP) and a 77 % (p < 0.05) decrease in high frequency activity (HF). When all the subjects were pooled, the changes in HRV in the supine position were correlated to the changes in aerobic capacities, i.e., HF, LF and TP were correlated to VO(2RCP) and HR, HF and TP were correlated to PRCP. This study confirms the relationship between HRV and changes in aerobic capacity, therefore highlighting the potential value of HRV for monitoring altitude training adaptations.     

The effect of age and gender on heart rate variability after endurance training

PURPOSE: This research investigated the age and gender differences in cardiovascular adaptation to a standardized/quantified endurance-training program that included two taper periods. METHODS: The latter was analyzed from spectral analysis of electrocardiogram records of heart rate variability (HRV) at rest in groups of young (19-21 yr) and middle aged (40-45 yr), mixed gender groups (6 males and 6 females), pre- and poststandardized training. All subjects were recreational runners who completed the same 12-wk running program. Before, and subsequent to training, HRV was measured during supine rest and submaximal cycling. RESULTS: There was a significant decrease in heart rate both at rest (2.7 +/- 0.45 beats x min-1) and during submaximal exercise (8.1 +/- 0.67 beats x min-1) in both age groups after training. After training, total spectral power increased (560.7 +/- 308.9 ms2), as well as high-frequency power (362.3 +/- 405.5 ms2), in both age groups at rest. The young group showed a greater increase in total power (849.0 +/- 308.7 ms2) after the training program. CONCLUSION: It is concluded that a well-designed 12-wk endurance-training program will decrease resting and submaximal heart rate in both younger and older adults. The significant increase in HRV, total power, and high-frequency power in all groups after endurance training indicates that HRV measurement appears to provide an effective, noninvasive assessment of cardiovascular adaptation to aerobic training.     

Aerobic training and cardiovascular responses at rest and during exercise in older men and women

PURPOSE: The effects of an intense 8-wk aerobic training program on cardiovascular responses at rest and during exercise, including heart rate variability (HRV) as an expression of autonomic modulation, were evaluated in subjects over 70 yr (mean: 73.9 +/- 3.5 yr). METHODS: Before and after training in 7 men and 8 women: a) heart rate (HR), blood pressures (BPs), pulse pressure (PP), and oxygen uptake were measured at rest, during, and after exhausting incremental exercise; b) HRV power spectra were calculated at rest in supine and sitting, and during and after two submaximal constant loads (5 min). Power in low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, >0.15 Hz) bands were expressed as a percent of total power minus power < 0.04 Hz. RESULTS: After training: a) at rest HR and HRV parameters (in both body positions) were unchanged, whereas BPs decreased; b) peak cycle resistance and oxygen consumption increased by 25% and 18%, respectively, but no change in maximal HR and BPs were found; c) during submaximal loads HR was unchanged at the same metabolic demand, whereas SBP and DBP were lower than before at low loads whereas PP was unchanged. LF power decreased and HF increased at oxygen uptakes above about 0.7 L.min-1 similarly before and after training; and d) recovery of all parameters was similar to pretraining and complete after 10 min CONCLUSIONS: The increase in exercise capacity without changes in cardiovascular parameters suggests that 8 wk of aerobic training augmented peripheral gas exchange but not delivery to muscle. The lack of effect on HRV indicates that the improvements in aerobic power and cardiac autonomic modulation, at least in subjects over 70 yr, are dissociated. Moreover, the metabolic demand seems to be the main factor for the changes in HRV power spectra that occur during exercise.     

立位-下体负压时心血管指标的变化

目的了解立位 -下体负压 (HUT +LBNP)期间心血管系统的变化 ,确定心律变异和脉图两种方法在评价心血管调节功能中的作用。方法观察 1 6名被试者在 75°头高位倾斜加 - 4kPa下体负压 2 0min期间血压、脉图、心律变异和脑血氧饱和度的变化。结果 ( 1 )HUT +LBNP可引起被试者出现明显的心率、血压、规 -化低频峰功率 (LFn)、LFn/HFn增加 ,脑血氧饱和度、心电T波和规 -化高频峰功率(HFn)下降 ;( 2 )晕厥前出现明显的血压、心率和脑血氧饱和度下降 ;( 3)低耐力组在HUT +LBNP初期的心率明显高于高耐力组 ;( 4 )HUT +LBNP时脉搏波波形发生很大变化 ,无法进行分析。结论HUT +LBNP是一种负荷量较高的立位耐力检查方法 ,可充分暴露被检者在立位中的心血管调节功能 ;脉图检测方法不能作为评价被试者HUT +LBNP耐力的方法。     

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。     

Relationship between the hemodynamic disorders in cosmonauts on short-term space flights and orthostatic stability]

Comparative investigation of the hemodynamic responses of cosmonauts at rest, during occlusive leg plethysmography, and LBNP in relatively short (less than a month) space flights were performed to tie up these measurements with post-landing orthostatic stability (OS). The decreased LBNP tolerance in flight that correlated later on with impaired reactions to both active and passive orthostatic testing are attributed, among other reasons, to deficient vasoconstriction of the main arteries and over-extendibility of veins in the lower extremities. Results of ultrasonic investigations of hemodynamics during LBNP tests before and after space flight and data of leg venous extension in SF can and should be used in predicting cosmonaut's orthostatic status post flight.     

Comparison of 70 degrees tilt, LBNP, and passive standing as measrues of orthostatic tolerance.

The present study was performed to assess the reliability of lower body negative pressure (LBNP) as a test of orthostatic tolerance. The need for this assessment arose from the prior observation in this laboratory that some subjects show wide day-to-day variation in heart rate responses to LBNP. The extent of these variations was so great as to a raise a serious question as to the value of LBNP as a measure of study-induced alterations (e.g. those produced by bedrest or weightlessness) in orthostatic tolerance. Five healthy volunteers were subjected to a series of tests, consisting of 70 degrees tilt, LBNP, and passive standing. on three occasions preceding and three occasions following a 2 week period of bedrest. Study results show that it is possible to subdivide the volunteers into subgroups which show either great or little day-to-day variability in any of the three tests. All three tests reaveled bedrest-induced alterations in orthostatic tolerande quite adequately. Of the three tests studied, LBNP most frequently resulted in the largest test-induced heart rate alterations, followed by quiet standing and, finally 70 degrees tilt     

下体负压下的心率变异分析

为探讨下体负压下的心率变异变化及其与血液动力这指标的关系，４０名健康男性参加了下体负压实验，用Ｈｏｌｔｅｒ记录了受试者Ｖ５导联心电图，并进行了心率变异（ＨＲＶ）分析；用超声多谱勒技术测定ＳＶ，ＣＯ。结果表明：在ＬＢＮＰ过程中两组受试者均出现了ＨＲＶ的降低，尤以高频谱质量（ＨＦ）降低显著，ＬＦ／ＨＦ在ＬＢＮＰ过程中呈升高趋势，耐力低者的ＬＦ／ＨＦ升高比耐力良好者明显，提示：晕厥前症状的发生可能是由于     

头低位卧床7d对立位心肺循环功能的影响

目的观察短期模拟失重对立位心肺循环功能的影响,为进一步研究失重时心血管功能下降机理积累资料。方法６名健康男性被试者,头低位６°卧床７ｄ。分别观察卧床前、后立位心肺循环功能的变化。心肺循环功能检测选用ＸＸＨ－２０００型小循环心功能检测仪。结果头低位卧床７ｄ致被试者立位耐力降低,卧床后右心室射血期（ｊ－ｚ）缩短,右心室排血效率降低（Ｑ－ｊ／ｊ－ｚ升高）,提示右心功能减退。心血管调节适应性反应减弱,右心功能储备降低。结论ｃ波高度（ｈｃ）、ｃ波高度与Ｚ波高度的比值（ｈｃ／ｈｚ）可作为评价立位耐力或预测立位晕厥的指标;小循环心功能检测法评价立位心肺循环功能的变化有一定的前景。     

Aerobic fitness in women and responses to lower body negative pressure

High aerobic fitness may be associated with impaired responsiveness to orthostatic challenge. This could be detrimental to astronauts returning from spaceflight. Thus, we examined the cardiovascular responses of a group of 45 healthy women to graded lower body negative pressure (LBNP) through 5 min at -50 mm Hg or until they become presyncopal. The ages (range = 23-43 years, mean = 30.4) and peak aerobic capacities (range = 23.0-55.3 ml.kg-1.min-1, mean = 37.8) of these subjects paralleled those of the women astronauts. We monitored heart rate, stroke volume, cardiac output, Heather index of contractility, arterial pressure, peripheral resistance, change in calf circumference, and thoracic impedance (ZO)--a measure of fluid in the chest. The women in this study exhibited the same response pattern to LBNP as previously reported for male subjects. VO2peak of the six subjects who became presyncopal was not different from VO2peak of the tolerant subjects. At rest, only systolic and mean arterial pressures were significantly correlated with VO2peak. Percent changes in calf circumference (i.e. fluid accumulation in the legs) at -30 and -40 mm Hg were the only responses to LBNP significantly related to VO2peak. The greater pooling of blood in the legs during LBNP by women with higher aerobic fitness, and lower percent body fat may be related to more muscle tissue and vasculature in the legs of the more fit subjects. These data indicated that orthostatic tolerance is not related to aerobic capacity in women, and orthostatic tolerance need not be a concern to aerobically fit women astronauts.     

提踵动作对下体负压耐力的影响

目的验证提踵动作对提高下体负压耐力的有效性,并探讨其可能的作用机制。方法健康男性志愿者10名,在下体负压(LBNP)条件下分别随机进行2次头高位倾斜检查(HUT)测定其下体负压耐力。一次为志愿者的基础下体负压耐力(对照组),另外一次要求志愿者在LBNP条件下做提踵动作,直至耐力终点(提踵组)。结果提踵组下体负压耐受时间(DNP)和累计应激指数(CSI)均显著增加(P<0.05)。在下体负压过程中,提踵组平均动脉压呈升高趋势,心率增加呈降低趋势,每搏量增加,且均在-40 mmHg及-50 mmHg时达到显著水平(P<0.05)。结论提踵动作可以提高下体负压耐力,可望作为航天员在长期太空飞行后引起立位耐力不良时的应对措施,也可作为血管迷走性晕厥患者的预防措施和治疗手段。     

Characteristics of the reactions to active orthostatic and water loading tests in persons with varying resistance to +Gz loads

Thirty-seven healthy male test subjects, aged 19-21, with different +Gz acceleration tolerance were examined. Their blood pressure (BP) and heart rate (HR) during 5-min tilt tests and 2% water loading tests were measured 2-3 weeks prior to centrifugation. Quantitative evaluation of orthostatic tolerance using an orthostatic index and BP and HR responses to tilt tests before and after water loading revealed specific features of cardiovascular regulation in the subjects with high and low +Gz acceleration tolerance. The negative predictive indicators include: decreased BP, HR and cardiac index in the supine position in combination with high orthostatic tolerance, as well as decreased orthostatic tolerance in combination with a lower function of vasoconstrictor mechanisms in the upright position and a lower sensitivity of carotid sinus reflexes to blood volume changes during tilt and water loading tests. When examining test subjects with high +Gz tolerance, preference should be given to those who can well tolerate tilt tests and show moderately high BP and HR in the supine position, as well as to those who exhibit a noticeable increment of diastolic BP during 5-min tilt tests.