Blood pressure and plasma renin activity as predictors of orthostatic intolerance

Some physiological responses to head-up tilt and 3 h standing were evaluated in 13 dehydrated subjects. Seven of the subjects proved to be orthostatically intolerant (INT), exhibiting presyncopal symptoms. Before the symptoms manifest themselves the INT subjects had consistently lower (p less than 0.05) systolic blood pressures, generally lower diastolic and pulse pressures, and elevated (p less than 0.05) plasma renin activity (PRA) compared to the tolerant (TOL) subjects. Plasma vasopressin usually increased more in the INT subjects, but appeared to be related to the severity of presyncopal symptoms rather than to the upright posture per se. It is concluded that systolic and pulse pressures, with PRA, may allow discrimination between TOL, and potentially INT individuals; i.e., predict orthostatic intolerance. It is suggested that dehydration could provide a valuable physiological model for elucidating the causes of orthostatic intolerance.     

有氧锻炼前后立位应激下血压变异性的比较

目的阐明下体负压（ＬＢＮＰ）作用下血压变异性的特征，以及有氧锻炼是否对其有一定影响。方法用常规ＡＲ谱、时变ＡＲ谱、粗粒化谱分析（ＣＧＳＡ）及近似熵（ＡｐＥｎ）四种方法，分析六个月有氧锻炼前、后大学生在两种ＬＢＮＰ作用下的收缩压变异性（ＳＢＰＶ），并与一组中、长跑运动员的结果进行横向比较。结果ＬＢＮＰ作用时，ＳＢＰＶ信号谐波成份的总功率及低频段（ＬＦ）功率增大，分形成份的谱指数（无显著变化，而ＡｐＥｎ则呈持续升高变化。有氧锻炼后，ＬＢＮＰ作用下各种ＳＢＰＶ指标的响应变化较锻炼前并无显著差别。大学生组与运动员组之间亦无显著差别。结论ＳＢＰＶ信号与心率变异性（ＨＲＶ）迥然不同：ＬＢＮＰ作用下，ＳＢＰＶ的ＬＦ成份被进一步激活，信号的复杂度显著升高；但ＳＢＰＶ信号的这种特征性变化并不受有氧锻炼的影响。     

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.     

立位耐力不良飞行员的血液动力学指标与心率变异性的改变

目的 探讨易发血管神经性晕厥飞行员的评价方法方法对３０例有晕厥史的立位耐力不良飞行员（阳性组）２０例有晕厥史的立位耐力正常飞行员（阴性组）和１５例健康飞行员（对照组），通过立位耐力结合心率变异性（ＨＲＶ）分析进行血压、心率与时域、频域指标的比较，按照国际常用标准进行判断分析。结果 阳性组立位耐力试验前平均心率（ＨＲ）、收缩压（ＳＢＰ）１、舒张压（ＤＢＰ）与阴性组、对照组比较，无显著性差异。试验后，     

Heart rate variability, blood pressure variability, and baroreflex sensitivity in overtrained athletes.

OBJECTIVE: To assess the effects of abruptly intensified physical training on cardiovascular control. DESIGN: Retrospective longitudinal study. SETTING: Research laboratory. PARTICIPANTS: Ten healthy athletes (5 men and 5 women) from track and field as well as triathlon. INTERVENTIONS: A 2-week training camp, including daily stepwise increasing cycling tests, running of 40 minutes, and additional cycling of 60 minutes. MAIN OUTCOME MEASUREMENTS: Time and frequency domain parameters of resting heart rate and blood pressure variability (HRV and BPV) and baroreflex sensitivity (BRS), before, during, and after the training camp. RESULTS: We found significantly reduced HRV during the training camp (mean beat-to-beat interval: 1042 [937 to 1194] ms vs. 933 [832 to 1103] ms vs. 1055 [947 to 1183] ms, P < 0.01; root-mean-square of beat-to-beat interval differences: 68 [52 to 95] ms vs. 52 [38 to 71] ms vs. 61 [48 to 78] ms, P < 0.05). Further, BRS was significantly reduced: 25.2 (20.4 to 40.4) ms/mmHg vs. 17.0 (12.9 to 25.7) ms/mmHg vs. 25.7 (18.8 to 29.1) ms/mmHg, P < 0.05. These effects disappeared at a large degree after 3 to 4 days of recovery. CONCLUSION: Abruptly intensified physical training results in an altered autonomic cardiovascular activity towards parasympathetic inhibition and sympathetic activation that can be monitored by means of HRV and BRS analyses and might provide useful markers to avoid the overtraining syndrome.     

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。     

Sodium bicarbonate ingestion and individual variability in time-to-peak pH

This study determined variability in time-to-peak pH after consumption of 300 mg kg^?1 of sodium bicarbonate. Seventeen participants (mean ± SD: age 21.38 ± 1.5 years; mass 75.8 ± 5.8 kg; height 176.8 ± 7.6 cm) reported to the laboratory where a resting capillary sample was taken. Then, 300 mg kg^?1 of NaHCO₃ in 450 ml of flavoured water was ingested. Participants rested for 90 min and repeated blood samples were procured at 10 min intervals for 60 min and then every 5 min until 90 min. Blood pH concentrations were measured. Results suggested that time-to-peak pH (64.41 ± 18.78 min) was variable with a range of 10–85 min and a coefficient of variation of 29.16%. A bimodal distribution occurred, at 65 and 75 min. In conclusion, athletes, when using NaHCO₃ as an ergogenic aid, should determine their time-to-peak pH to best utilize the added buffering capacity this substance allows.     

fMRI of human olfaction at the individual level: Interindividual variability

Purpose:

To determine whether the range of normal variation of human olfactory functional magnetic resonance imaging (fMRI) activations in healthy single subjects is compatible with the detection of atypical patterns.

Materials and Methods:

In an event‐related olfactory experiment, the variability of fMRI activation in six bilateral olfactory areas known to be affected in neurodegenerative diseases was measured in a region of interest (ROI) analysis in terms of intensity, localization, and overlap on 51 subjects. fMRI measurements were compared against measurements from a visual experiment performed on 25 subjects.

Results:

Olfaction induced activations with low intensity, high variability, and a 4‐fold lower contrast‐to‐noise ratio (CNR) than vision. Even in the best case (piriform cortex), mean pairwise activation overlap was still less than 40%. None of the olfactory ROIs showed significant activation for all subjects at the permissive threshold of P < 0.001. A gender‐dependent significantly stronger activation was found in the bilateral piriform cortex of male subjects.

Conclusion:

Linking t‐statistics and CNR showed that for all olfactory ROIs, CNR is either near or below the estimated threshold of 0.73 found to be necessary to obtain significant activations. In our experimental conditions the low reliability of olfactory activations should prompt major reservations over using fMRI of human olfaction as a diagnostic tool in single subjects. J. Magn. Reson. Imaging 2013;37:92–100. © 2012 Wiley Periodicals, Inc.     

Subject variability of shoulder abduction strength testing

To quantify normal biological variability of shoulder abduction strength testing with an isokinetic and a hand-held dynamometer, we tested nine healthy subjects over a clinically relevant period. One side was tested with a Cybex at 60 deg/sec and the other with a hand-held dynamometer. Six maximal trials, following warmup, were conducted on each of 5 days, separated by 1 to 2 weeks. Intraday correlations of individual trials ranged from 0.82 to 0.995 for hand-held dynamometer, and 0.88 to 0.996 for Cybex. Interday correlations ranged from 0.94 to 0.98 for hand-held dynamometer, and 0.88 to 0.97 for Cybex. The best values to use for Cybex interday variability were the average of the first three repetitions, and yielded standard errors of 8.6% to 19.2% of the sample mean. The average of the last three repetitions were the best for hand-held dynamometers, and yielded standard errors of 5.5% to 10.8%. There was a significant decline (P less than 0.05) in strength of the mean of the last three versus the mean of the first three daily repetitions on Day 1 and 4 for hand-held dynamometers, and a trend toward this on the other days, that was not seen with Cybex. Regression of average Day 1 values for Cybex and hand-held dynamometer yielded r = 0.86 (P less than 0.01) with a slope of 1.07 indicating good agreement between modalities. In conclusion, intraday/interday correlations were high for Cybex and hand-held dynamometer. Interday variability was minimized by using the mean score of the first three and last three repetitions for Cybex and hand-held dynamometer, respectively. Changes in Cybex and hand-held dynamometer strength of less than 19% and 11%, respectively, are within the area of "measurement error" and should therefore not be considered clinically significant.     

战斗机飞行员长时血压变异性分析

目的探讨飞行员动态血压（ＡＢＰ）昼夜分布特征及其变异范围，为高性能战斗机飞行员心血管体能选拔提供依据。方法对６０名男性战斗机飞行员进行２４小时动态血压监测与不同时间锁定方法学分析比较。结果①与正常人群一样，飞行员２４ｈ－ＡＢＰ存在明显的昼夜循环节奏变化，即白天血压高，夜间血压低，呈现一种典型的“勺型”分布。但血压平均水平较一般正常人群低；②飞行员２４ｈ血压变异（ＢＰＶ）显著大于白昼ＢＰＶ，白昼ＢＰＶ显著大于夜间ＢＰＶ；③不同时间锁定窗口所得夜间ＢＰＶ参值及血压昼夜差值之间存在明显差异。结论２４ｈ－ＢＰＶ分析能为高性能战斗机飞行员心血管调节机能提供重要信息     

立位耐力不良飞行员模拟飞行中心理生理反应与心率变异性分析

目的探讨立位耐力不良飞行员模拟空中环境下心脏自主神经功能调节状态和心理生理反应特点，为空中晕厥的诊断提供客观的评价方法。方法对２２名立位耐力不良（不良组）飞行员进行了连续动态心电记录和模拟飞行条件下的心理生理参数测定与心率变异性（ＨＲＶ）分析，并与１５名立位耐力正常的健康飞行员（健康组）做了对比。结果不良组飞行员在模拟仪表飞行中心理生理储备能力明显降低，表现为完成两项任务的质量和处理信息速度的能力较健康组低（Ｐ＜０．０１）；心血管自主神经功能严重失调；心理生理储备值与ＨＲＶ多数指标之间存在明显的相关性。结论结合模拟仪表飞行条件下的心理生理负荷评定和ＨＲＶ分析能较客观地反映立位耐力不良飞行员心血管自主神经功能障碍的发生机制和调节规律，为空中晕厥的诊断提供量化的指标。     

Intense endurance training on heart rate and blood pressure variability in runners.

Physical training with incomplete recovery times can produce significant fatigue. A study of cardiovascular responses showed that there is a sympathetic and a parasympathetic form of fatigue. PURPOSE: The purpose of this experimentation was to measure the effects of intense endurance training on autonomic balance through a spectral analysis study of the heart rate (HR) and systolic blood pressure (SBP). METHODS: Eight elite runners were tested twice: after a relative rest period (RRP) of 3 wk and after an 12-wk intense training period (ITP) for endurance. At the end of each phase, the subjects were tested by means of a VO2max test and a tilt-table test. RESULTS: The resting heart rate (HR) variability was lower (P < 0.001) in the intensive training phase. Likewise, there were differences in the low-frequency (0.04-0.150 Hz; LF) and high-frequency (0.150-0.500 Hz; HF) components and the LF/HF ratio of the HR spectral analysis. The LF spectral power was significantly lower in the supine position (P < 0.05) during ITP. Upright tilting was accompanied by a 22.6% reduction in HF values during the rest period, whereas in ITP the HF spectral power rose by 31.2% (P < 0.01) during tilt, characterizing a greater parasympathetic system control. Sympathetic control represented by the LF/HF ratio regressed markedly (P < 0.01) in response to the tilt test in ITP. CONCLUSIONS: The spectral analysis of SBP in the high frequencies shows that the changes in cardiac parameters are coupled with a decrease in sympathetic vasomotor control (-18%) and a reduction in diastolic pressure (-3.2%) in the response to the tilt test at the end of ITP. Spectral analysis could be a means of demonstrating impairment of autonomic balance for the purpose of detecting a state of fatigue that could result in overtraining.     

Blood pressure responses to LBNP in nontrained and trained hypertensive rats.

To study the influences of 16 wk of endurance training on the reflex regulation of resting blood pressure, nontrained (NT) and trained (T) female hypertensive rats (SHR) were subjected to conditions of lower body negative pressure (LBNP). Measurements of muscle cytochrome oxidase activity and run time to exhaustion indicated that the animals were endurance trained. The rats (NT = 6, T = 7) were tranquilized with 300-600 micrograms.kg-1 diazepam (IV) before heart rates and blood pressures were measured over a range of 2.5-10.0 mm Hg of negative pressure. When subjected to conditions of LBNP, the reflex tachycardia of the T group was greater than the NT at the lower (-2.5 and -5.0 mm Hg) negative pressures. Although arterial pressure declines were similar in both groups, the T group experienced significantly less of a decline in central venous pressure than the NT animals. When chlorisondamine was used as a ganglionic blocker (2.5 mg.kg-1, IV), the fall in CVP at 10 mm Hg negative pressure was greater for the NT group while the fall in the initial systemic arterial pressure was more for the T group. From these results we concluded that training had altered the interaction between cardiopulmonary and arterial baroreflexes in these hypertensive rats and a nonneural component had been altered such as cardiac function.     

Blood pressure during leg extension in children

This study investigated blood pressure responses (BP) during bilateral leg extension in healthy children at different numbers of repetitions. BP was measured non-invasively during 1 repetition maximum (1RM), 5 repetitions at 85-90% of 1RM (5?R), 30 repetitions at 35-40% of 1RM (30?R) and during 5?s of maximal isometric work (5SM). It is important to investigate if maximal strength testing in healthy children provokes an unfavourable rise in BP, in order to be able to do further research on hypertensive risk groups of children. 39 (18 male and 21 female) healthy children (10.5±2.0 years old) participated in this study. Peak BP values and peak HR increased significantly with increasing number of repetitions. Peak BP increased from 1RM (144±16/110±19?mmHg) to 30R (170±26/123±21?mmHg) and peak HR increased from 1RM (122±10?bpm) to 30?R (147±14?bpm). 30R also gave significantly higher BP and HR than 5SM (156±24/120±23?mmHg and 131±16?bpm, respectively). The boys had significantly higher diastolic BP during 1RM than the girls and significantly higher BP during 5SM. In conclusion, maximal strength testing induced lower increases in BP than submaximal strength testing with more repetitions, and may be performed in healthy children within safe BP limits (相似文献   

Hypervariable regions of DNA for parentage testing and individual identification

Summary Four kinds of DNA probes that recognize hypervariable regions (HVR) were studied for parentage testing and individual identification. Allele frequencies and their confidence intervals among unrelated Japanese individuals were obtained. Codominant segregation of the polymorphism was confirmed in family studies. Two a priori probabilities were calculated for each HVR locus: the exclusion probabilities for an alleged father/mother/ child trio and for an alleged parent/child duo, and the probabilities of matching of genotypes of two unrelated individuals or two siblings. The ease of availability of the probes and their highly discriminating polymorphic patterns mean they could be very useful for forensic purposes.     

The effect of hypoxia and exercise on heart rate variability,immune response,and orthostatic stress

Hypoxia with exercise is commonly used to enhance physiological adaptation in athletes, but may prolong recovery between training bouts. To investigate this, heart rate variability (HRV), systemic immune response, and response to an orthostatic challenge were measured following exercise in hypoxia and air. Eleven trained men performed a 10‐km cycling time trial breathing hypoxia (16.5 ± 0.5% O₂) or air. HRV and the heart rate response to an orthostatic challenge were measured for 3 days before and after each trial, while venous blood samples were collected pre‐, 0, 2, and 24 h post‐exercise. Hypoxia had no significant effect compared with air. Subgroup analysis of those who had a drop in oxyhemoglobin saturation (SpO₂) > 10% between hypoxia and air compared with those who did not, demonstrated a significantly altered HRV response (△HFnu: ?2.1 ± 0.9 vs 8.6 ± 9.3, △LFnu: 2.1 ± 1.0 vs ?8.6 ± 9.4) at 24 h post‐exercise and increased circulating monocytes (1.3 ± 0.2 vs 0.8 ± 0.2 × 10⁹/L) immediately post‐hypoxic exercise. Exercise and hypoxia did not change HRV or the systemic immune response to exercise. However, those who had a greater desaturation during hypoxic exercise had an attenuate recovery 24 h post‐exercise and may be more susceptible to accumulating fatigue with subsequent training bouts.     

An in vitro study of individual ankle muscle actions on the center of pressure

The objective of this study was to correlate the effects of muscle force on the movement of the center of pressure (COP) for increased clinical utility of the COP measurement. Five fresh frozen cadaveric specimens were used to apply a 49 N sinusoidal muscle force to isolated or grouped extrinsic ankle muscles, and a constant ankle joint reaction force at different tibial positions. The muscle force and the vertical ground reaction force (GRF) play the role of a mechanical lever system so that the differential COP movement can be interpreted as a moment arm for the vertical GRF.     

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。