应激条件下心血管调节功能的模糊聚类和系统分析

27名被试者在下身负压作用下,采用无创性心功能指标和模糊聚类分析、进行心血管调节功能状态分类,以系统分析的指标,对心血管调节功能状态评价。结果表明,三类人员中,以国Ⅰ类人具有良好储备和快速调节适应能力,表现为心泵与血管调节能力均优,Ⅱ类人是以血管调节为特点的功能良好者,Ⅲ类人反应过于灵敏和不稳定、储备与适应性差、血管与泵血能力弱、系统调节功能差。文中对系统调节功能与机体植物神经功能状态进行讨论,并认为交感神经活动强者有较好耐受性。采用数学方法和系统分析,对人体心血管谓节功能状态分类与评价,值得探讨。     

模拟高原游泳运动对大鼠血液粘滞度及心功能的影响

目的:研究低氧复合游泳运动对大鼠血液流变学及心脏功能的影响.方法:大鼠分为三组:常氧对照组、低氧组和低氧复合游泳运动组.低氧大鼠每天在模拟海拔4 000 m 低氧1.5 h后,升至5 000 m,持续减压23 h/d,共5周.低氧运动大鼠每天在4 000 m模拟海拔游泳运动1 h(6 d/w),然后升至5 000 m.多导生理记录仪测定心脏功能,E-型锥板粘滞度仪测定血液粘滞度,放射性生物微球法测定心输出量.结果:低氧时,大鼠血球压积明显升高,全血粘度显著增加.低氧复合运动未引起血球压积的进一步升高,血液粘滞度显著降低.低氧组大鼠左、右室心肌最大舒缩速度显著提高,低氧复合运动后最大舒缩速度进一步提高,心输出量显著增加.结论:在一定程度的低氧下,适当的体力活动可显著增强心脏功能,显著降低血液粘滞度.这种改变有利于改善低氧时机体各器官和组织的供氧状态,促进习服.     

一种全新的无创伤心功能STI微机检测仪

患心脏、心血管病的人数逐年上升。推广该疾病的早期预报、诊断应用技术,对提高人类健康水平和在生理、临床医学上进一步挖掘心脏信息有着重要意义。无创伤心功能STI微机系统对心脏功能的评定有实用意义并与常规检测仪相比有其突出优点。作者在研制的新一代心功能STI微机检测仪时,从提高系统各方面性能出发,力图使检测系统工作更准确可靠,操作更方便。本文就该系统的软件、硬件二方面简要叙述其构成与设计上独具的一些特点。     

用心脏舒张期与收缩期时限比值评估青少年心脏功能

目的：观察青少年在安静状态及最大运动量状态下心脏舒张期时限与收缩期时限比值（D/S）的变化情况,并运用该指标对青少年心脏功能的评估进行探讨。方法：选取重庆市主城区中学309名（男159名,女150名）青少年为研究对象,受试者完成最大运动量的台阶运动,在安静状态和运动后即刻进行D/S比值的测试。根据安静状态D/S值的大小范围将受试者心脏功能分级为优（ D/S≥2）、良（1.5≤D/S<2）、中（1≤D/S<1.5）、差（D/S<1）。结果：安静状态下男生心脏功能评定为优、良、中、差的占比分别为： 7.5%、49.1%、 40.9%、2.5%;女生分别为： 5.3%、48.0%; 44.7%、2.0%。运动后男、女青少年D/S值都明显下降,但心脏功能评定等级高的受试者运动后D/S仍高于等级低的受试者。结论：本次研究的青少年虽有过半心脏功能处于健康状态,但处于亚健康状态的比例较高,有少部分学生心脏功能较差,其心脏健康应得到高度重视;心脏功能等级越高的学生运动后心脏供血时间越长,其心脏功能更好。应用D/S值可以有效评估青少年心脏供血时限的相关情况;对青少年心脏功能进行分级可以针对不同分级群体制定有针对性的运动训练,同时预防心脏安全事故的出现。该评估方法操作简单、客观,可作为一种日常的心脏监测手段在学校普及。     

低氧适应对缺氧性心功能损伤的保护作用及其机制探讨

缺氧对心脏功能的影响与缺氧的严重程度、发生速度及时程有关。本实检比较了急性缺氧与阶梯适应性缺氧对Ｗｉｓｔａｒ大鼠心脏功能及心肌收缩蛋白Ｃａ２＋,Ｍｇ２＋－ＡＴＰ酶的不同影响,结果表明,低氧适应组与急性缺氧组比较,左右心室的±ｄｐ／ｄｔｍａｘ、收缩指数等心功能指标均有显著的改善,心肌收缩蛋白Ｃａ２＋,Ｍｇ２＋－ＡＴＰ酶活性也显著高于急性缺氧组。从而说明,动物经低氧适应后,心脏的代偿功能得到充分发挥,从面减轻缺氧对心脏的损伤。心肌收缩蛋白Ｃａ２＋,Ｍｇ２＋－ＡＴＰ酶的改善可能是心脏代偿机制的生物化学基础之一。     

ELABELA促进心肌梗死运动康复机制

G蛋白偶联受体Apelin receptor (APLNR, APJ)早期配体ELABELA/Toddler/Apela (ELA)是一种肽类激素,对心血管系统早期发育必不可少。心肌梗死(myocardial infarction, MI)后,ELA表达代偿性升高,外源性ELA干预具有靶向抑制氧化应激、细胞凋亡并促进心肌新生、抵抗MI所致心衰的作用,对改善病理心脏重塑和提升心功能等效果显著。运动可促进内源性ELA发挥MI心脏的保护作用。现对ELA结合运动干预改善氧化应激引起的细胞凋亡并缓解缺血心脏功能障碍等文献进行梳理,提出运动促进MI心脏功能改善与康复的新观点,从而为MI患者临床度过急性期后进行运动康复研究提供有价值的理论依据。     

运动训练和体位对安静负荷及恢复期心功能的影响

运动及恢复过程中心功能改变及运动训练对心功能影响的研究虽有不少报道,但关于多级小档距递增负荷中的心功能变化及不同体位对此变化的影响则报道甚少。本实验用无创法测定了不同体能的人在坐位和卧位下完成相同亚极量递增负荷过程中及恢复期的心功能指标,旨在进一步探讨运动负荷中及恢复期的心功能特点及运动训练和体位改变对它的影响。     

间歇性低氧适应的心脏保护

间歇性低氧（intermittent hypoxia,IH）是指一定时间间断地暴露于低氧环境,而其余时间处于常氧环境。IH是机体某种生理和病理状态下的低氧形式。研究表明：间歇性低氧适应（IHadaptation）,类似缺血预适应（ischemic preconditioning,IPC）和长期高原低氧适应（long-termhigh-altitude hypoxic adaptation,LHA）,具有明显的心脏保护作用,表现为增强心肌对缺血／再灌注损伤的耐受性、限制心肌梗死面积和形态学改变、抗细胞凋亡、促进缺血／再灌注心脏舒缩功能的恢复,以及抗心律失常。尽管IH对心脏的保护作用不容质疑,但其作用机制远未阐明。IH心脏保护作用可能涉及氧的运输、能量代谢、神经体液调节、抗氧化酶、应激蛋白、腺苷系统、ATP敏感钾通道、线粒体及其钙调控、一氧化氮和蛋白激酶等多方面机制,并受低氧处理方式、动物年龄和性别等因素影响。IH心脏保护持续时间明显长于IPC,而对机体的不良影响远小于LHA,具有潜在的应用价值。     

49例先天性胎儿心脏疾病的静脉导管血流频谱分析

目的：不同的胎儿先天性心脏疾病通过不同的作用机制影响到胎儿心脏功能,会引起胎儿体内血循环的不同改变。静脉导管是胎儿血循环中重要的组成,也会随之出现相应的频谱改变。通过对49例合并先天性心脏疾病胎儿的静脉导管血流频谱及参数进行分析,研究胎儿不同类型心脏疾病对静脉导管（DV）血流频谱的影响。方法：选取2009年1月至2012年12月间我们在产前超声检查中发现的49例合并先天性心脏疾病的胎儿,分别测量DV血流频谱并进行参数分析,根据DV频谱是否正常分为两组。结果：DV频谱正常组有29例（59.18%）,表现为S波、a波的流速和方向正常,PVIV及DVRI指标位于正常范围。DV频谱异常组有20例,表现为S波流速降低、a波缺失或反向,PVIV及DVRI升高。结论：DV血流频谱和参数是评价胎儿心功能的良好指标。不同种类胎儿心脏发育异常对胎儿心功能影响的作用机制不同,其DV频谱也有着不同改变。通过对DV频谱的波形和参数分析,了解胎儿心脏异常的病生理机制,评价其严重程度和预后,这对于指导临床诊疗有着重要意义。     

高原移居战士运动后心肌酶和心功能的变化及红益胶囊的干预作用

目的：探讨高原移居战士运动后心肌酶和心功能的变化及红益胶囊的干预作用。方法：平原入伍到高原6个月~24个月的健康男性战士8名,分别在服用红益胶囊前及服药5 d、8 d,检测运动前静息状态、运动后即刻的心肌作功指数（Tei指数）、左心室射血分数（LVEF）及30 min时的血清肌酸激酶同功酶-MB（CK-MB）和心肌肌钙蛋白I （cTnI）。结果：在静息状态下,服药前、服药5 d、8 d运动后Tei指数、血清C K-MB、cTnI水平均明显增高,LVEF均明显降低（P<0.01）;与服药前运动后比较,服药8 d,运动后Tei指数、血清CK-MB、cTnI水平均明显降低、LVEF明显升高（P<0.01）。结论：平原移居高原久居战士在高原中等强度负荷运动时,有明显的心肌损伤及心功能降低。红益胶囊对减轻人体在高原体力负荷劳动时心肌缺氧性损伤,增强心功能有明显作用。     

Exercise plus volume loading prevents orthostatic intolerance but not reduction in cerebral blood flow velocity after bed rest

This study tested the hypothesis that reduction in cerebral blood flow (CBF) during orthostatic stress after bed rest can be ameliorated with volume loading, exercise, or both. Transcranial Doppler was used to measure changes in CBF velocity during lower body negative pressure (LBNP) before and after an 18-day bed rest in 33 healthy subjects. Subjects were assigned into four groups with similar age and sex: 1) supine cycling during bed rest (Exercise group; n = 7), 2) volume loading with Dextran infusion after bed rest to restore reduced left ventricular filling pressure (Dextran group; n = 7), 3) exercise combined with volume loading to prevent orthostatic intolerance (Ex-Dex group; n = 7), and 4) a control group (n = 12). LBNP tolerance was measured using a cumulative stress index (CSI). After bed rest, CBF velocity was reduced at a lower level of LBNP in the Control group, and the magnitude of reduction was greater in the Ex-Dex group. However, reduction in orthostatic tolerance was prevented in the Ex-Dex group. Notably, volume loading alone prevented greater reductions in CBF velocity after bed rest, but CSI was reduced still by 25%. Finally, decreases in CBF velocity during LBNP were correlated with reduction in cardiac output under all conditions (r(2) = 0.86; P = < 0.001). Taken together, these findings demonstrate that volume loading alone can ameliorate reductions in CBF during LBNP. However, the lack of associations between changes in CBF velocity and orthostatic tolerance suggests that reductions in CBF during LBNP under steady-state conditions by itself are unlikely to be a primary factor leading to orthostatic intolerance.     

Effect of lower body negative pressure on orthostatic tolerance and cardiac function during 21 days head-down tilt bed rest

The purpose of the present study was to investigate the changes of orthostatic tolerance and cardiac function during 21 d head-down tilt (HDT) bed rest and effect of lower body negative pressure in the first and the last week in humans. Twelve healthy male volunteers were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mmHg LBNP sessions for 1 h per day from the 1st to the 7th day and from the 15th to the 21st day of the HDT, and six others served as control. Orthostatic tolerance was assessed by means of standard tilt test. Stroke volume (SV), cardiac output (CO), preejection period (PEP) and left ventricular ejection time (LVET) were measured before and during HDT. Before HDT, all the subjects in the two groups completed the tilt tests. After 10 d and 21 d of HDT, all the subjects of the control group and one subject of the LBNP group could not complete the tilt test due to presyncopal or syncopal symptoms. The mean upright time in the control group (15.0 +/- 3.2 min) was significantly shorter than those in the LBNP group (19.7 +/- 0.9 min). SV and CO decreased significantly in the control group on days 3 and 10 of HDT, but remained unchanged throughout HDT in the LBNP group. A significant increase in PEP/LVET was observed on days 3 and 14 of HDT in both groups. The PEP/LVET in the LBNP group was significantly lower on day 3 of HDT, while LVET in the LBNP group was significantly higher on days 3, 7 and 14 of HDT than those in the control group. The results of this study suggest that brief daily LBNP sessions used in the first and the last weeks of 21 d HDT bed rest were effective in diminished the effect of head-down tilt on orthostatic tolerance, and LBNP might partially improve cardiac pumping function and cardiac systole function.     

Hemodynamic and neuroendocrine predictors of lower body negative pressure (LBNP) intolerance in healthy young men.

Exposure to LBNP results in body fluid shift to lower extremities similarly as under influence of orthostatic stress. In susceptible persons it leads to syncope. For better understanding why certain individuals are more susceptible to orthostatic challenges it seemed necessary to collect more data on hemodynamic and neuroendocrine adjustments occurring before onset of presyncopal symptoms Accordingly, in this study heart rate (HR), blood pressure (BP), stroke volume (SV), cardiac output (CO), hematocrit, plasma catecholamines, adrenomedullin, ACTH and plasma renin activity (PRA) were measured in 24 healthy men during graded LBNP (-15, -30 and -50 mmHg). Thirteen subjects completed the test (HT group) whereas 11 had presyncope signs or symptoms at -30 mmHg or at the beginning of -50 mmHg (LT group). Comparison of these groups showed that LT subjects had lower baseline total peripheral resistance and higher plasma adrenomedullin. During LBNP plasma catecholamine and PRA increases were even greater in LT than in HT group while plasma adrenomedullin elevations were similar in both groups. Plasma ACTH increased only in LT group following presyncope symptoms. Low tolerant group showed more rapid decline of SV and CO than HT subjects from the beginning of LBNP. It is suggested that measurements of SV at the level of LBNP which did not evoke any adverse symptoms may be of predictive value for lower orthostatic tolerance.     

Skin surface cooling improves orthostatic tolerance in normothermic individuals

Previous studies suggest that skin surface cooling (SSC) preserves orthostatic tolerance; however, this hypothesis has not been experimentally tested. Thus the purpose of this project was to identify whether SSC improves orthostatic tolerance in otherwise normothermic individuals. Eight subjects underwent two presyncope limited graded lower-body negative pressure (LBNP) tolerance tests. On different days, and randomly assigned, LBNP tolerance was assessed under control conditions and during SSC (perfused 16 degrees C water through tube-lined suit worn by each subject). Orthostatic tolerance was significantly elevated in each individual due to SSC, as evidenced by a significant increase in a standardized cumulative stress index (normothermia 564 +/- 58 mmHg.min; SSC 752 +/- 58 mmHg.min; P < 0.05). At most levels of LBNP, blood pressure during the SSC tolerance test was significantly greater than during the control test. Furthermore, the reduction in cerebral blood flow velocity was attenuated during some of the early stages of LBNP for the SSC trial. Plasma norepinephrine concentrations were significantly higher during LBNP with SSC, suggesting that SSC may improve orthostatic tolerance through increased sympathetic activity. These data demonstrate that SSC is effective in improving orthostatic tolerance in otherwise normothermic individuals.     

Effect of 6-week endurance training on hemodynamic and neurohormonal responses to lower body negative pressure (LBNP) in healthy young men.

Endurance training is considered as a factor impairing orthostatic tolerance although an improvement and lack of effect have been also reported. The mechanisms of the changes and their relation to initial tolerance of orthostasis are not clear. In the present study, effect of moderate running training on hemodynamic and neurohormonal changes during LBNP, a laboratory test simulating orthostasis, was investigated in subjects with high (HT) and low (LT) tolerance of LBNP. Twenty four male, healthy subjects were submitted to graded LBNP (-15, -30 and -50 mmHg) before and after training. During each test heart rate (HR), stroke volume (SV) and blood pressure, plasma catecholamines, ACTH, adrenomedullin, atrial natriuretic peptide, and renin activity were determined. Basing on initial test, 13 subjects who withstood LBNP at -50 mmHg for 10 min were allocated into HT group and 11 subjects who earlier showed presyncopal symptoms to LT group. Training improved LBNP tolerance in six LT subjects. This was associated with attenuated rate of HR increase and SV decline (before training, at -30 mmHg deltaHR was 21 +/- 4 beats/min and deltaSV - -36+/- 8 ml while after training the respective values were 8 +/- 4 beats/min and -11+/- 6 ml). No differences in hemodynamic response were found in HT subjects and those from LT group whose LBNP tolerance was unchanged. In neither group training affected neurohormonal changes except inhibition of plasma ACTH rise in subjects with improvement of LBNP tolerance. It is concluded that some subjects with low orthostatic tolerance may benefit from moderate training due to improvement of cardiac function regulation.     

Effects of increased muscle perfusion pressure on responses to dynamic leg exercise in man

Ventilatory, cardiovascular and metabolic functions and work performance were studied in men performing incremental-load dynamic leg exercise until exhaustion. Part I: Responses to supine exercise were investigated in 8 subjects during exposure of the lower body to subatmospheric pressure at -6.67 kPa (-50 mm Hg) (Lower Body Negative Pressure, LBNP). Due to curtailment of stroke volume, cardiac output was reduced by LBNP over a wide range of work intensities, including heavy loads: ventilation, oxygen uptake and blood lactate concentrations increased with work load, but at lower rates than in the control condition. Part II: In 9 subjects, work performance was compared in three conditions: supine exercise with and without LBNP, and upright exercise. Performance in supine exercise was enhanced by LBNP, and was further improved in upright exercise. In supine exercise, the LBNP-induced reduction in blood lactate and enhancement of work performance are attributed to a more efficient muscle blood flow resulting from increased local perfusion pressure. This strongly suggests that the primary limitation of work performance was set by the peripheral circulation in working muscles rather than by cardiac performance. A similar mechanism may, in part, explain why work performance in dynamic leg exercise was greater in the upright than in the supine posture. It is also concluded that supine leg exercise during LBNP is a useful model of upright exercise, with regard to the central circulation and the circulation in working muscles.     

Reactions of the autonomic nervous system of students with different characteristics of higher nervous activity in the situation of examination stress

The influence of examination stress on the reactions of the autonomic nervous system in students with different levels of functional mobility of nervous processes (FMNP) was studied. More intense functioning of the cardiovascular system and the strain of all regulatory mechanisms during examination stress were characteristic of individuals with low FMNP, whereas students with high FMNP values were characterized by a weaker strain of the mechanisms of cardiac rhythm regulation, more economical activity of the cardiovascular system, and better performance on the examinations. The activation of humoral, metabolic, and sympathetic effects was observed in all the subjects under examination stress, along with decreased parasympathetic effects on the cardiac rhythm.     

Effect of skin surface cooling on central venous pressure during orthostatic challenge

Orthostatic stress leads to a reduction in central venous pressure (CVP), which is an index of cardiac preload. Skin surface cooling has been shown to improve orthostatic tolerance, although the mechanism resulting in this outcome is unclear. One possible mechanism may be that skin surface cooling attenuates the drop in CVP during an orthostatic challenge, thereby preserving cardiac filling. To test this hypothesis, CVP, arterial blood pressure, heart rate, and skin blood flow, as well as skin and sublingual temperatures, were recorded in nine healthy subjects during lower body negative pressure (LBNP) in both normothermic and skin surface cooling conditions. Cardiac output was also measured via acetylene rebreathing. Progressive LBNP was applied at -10, -15, -20, and -40 mmHg at 5 min/stage. Before LBNP, skin surface cooling lowered mean skin temperature, increased CVP, and increased mean arterial blood pressure (all P < 0.001) but did not change mean heart rate (P = 0.38). Compared with normothermic conditions, arterial blood pressure remained elevated throughout progressive LBNP. Although progressive LBNP decreased CVP under both thermal conditions, during cooling CVP at each stage of LBNP was significantly greater relative to normothermia. Moreover, at higher levels of LBNP with skin cooling, stroke volume was significantly greater relative to normothermic conditions. These data indicate that skin surface cooling induced an upward shift in CVP throughout LBNP, which may be a key factor for preserving preload, stroke volume, and blood pressure and improving orthostatic tolerance.     

Cardiovascular responses to an orthostatic challenge and electrical-stimulation-induced leg muscle contractions in individuals with paraplegia

The purpose of this study was to investigate the cardiovascular and haemodynamic responses that occur during moderate orthostatic challenge in people with paraplegia, and the effect of electrical stimulation (ES)-induced leg muscle contractions on their responses to orthostatic challenge. Eight males with complete spinal lesions between the 5th and 12th thoracic vertebrae (PARA) and eight able-bodied individuals (AB) volunteered for this study. Changes in heart rate (fc), stroke volume (SV), cardiac output (Qc), mean arterial pressure (MAP), total peripheral resistance (TPR), limb volumes and indices of neural modulation of fc, [parasympathetic (PNS) and sympathetic (SNS) nervous system indicators] were assessed during: (1) supine rest (REST), (2) REST with lower-body negative pressure at -30 torr (LBNP -30, where 1 torr = 133.32 N/m2), and (3) for PARA only, LBNP -30 with ES-induced leg muscle contractions (LBNP + ES). LBNP -30 elicited a decrease in SV (by 23% and 22%), Qc (by 15% and 18%) and the PNS indicator, but an increase in fc (by 10% and 9%), TPR (by 23% and 17%) and calf volume (by 1.51% and 4.04%) in both PARA and AB subjects, respectively. The SNS indicator was increased in the AB group only. Compared to LBNP -30, LBNP + ES increased SV (by 20%) and Qc (by 16%), and decreased TPR (by 12%) in the PARA group. MAP was unchanged from REST during all trials, for both groups. The orthostatic challenge induced by LBNP -30 elicited similar cardiovascular adaptations in PARA and AB subjects. ES-induced muscle contractions during LBNP -30 augmented the cardiovascular responses exhibited by the PARA group, probably via reactivation of the skeletal muscle pump and improved venous return.     

Cardiovascular responses to apneic facial immersion during altered cardiac filling.

The hypothesis that reduced cardiac filling, as a result of lower body negative pressure (LBNP) and postexercise hypotension (PEH), would attenuate the reflex changes to heart rate (HR), skin blood flow (SkBF), and mean arterial pressure (MAP) normally induced by facial immersion was tested. The purpose of this study was to investigate the cardiovascular control mechanisms associated with apneic facial immersion during different cardiovascular challenges. Six subjects randomly performed 30-s apneic facial immersions in 6.0 +/- 1.2 degrees C water under the following conditions: 1) -20 mmHg LBNP, 2) +40 mmHg lower body positive pressure (LBPP), 3) during a period of PEH, and 4) normal resting (control). Measurements included SkBF at one acral (distal phalanx of the thumb) and one nonacral region of skin (ventral forearm), HR, and MAP. Facial immersion reduced HR and SkBF at both sites and increased MAP under all conditions (P < 0.05). Reduced cardiac filling during LBNP and PEH significantly attenuated the absolute HR nadir observed during the control immersion (P < 0.05). The LBPP condition did not result in a lower HR nadir than control but did result in a nadir significantly lower than that of the LBNP and PEH conditions (P < 0.05). No differences were observed in either SkBF or MAP between conditions; however, the magnitude of SkBF reduction was greater at the acral site than at the nonacral site for all conditions (P < 0.05). These results suggest that the cardiac parasympathetic response during facial immersion can be attenuated when cardiac filling is compromised.