Assessment of the left ventricular diastolic reserve in essential hypertension: the acute saline load test

OBJECTIVE: The aim of this study was to evaluate the significance of the development of a restrictive response to an acute saline load, defined as an increase in the ratio of peak early to peak late diastolic transmitral flow velocity (E/A ratio) associated with a decrease in the deceleration time, in patients with mild to moderate untreated hypertension. BACKGROUND: Recognised abnormal patterns of transmitral diastolic flow include, from 'best' to 'worst': prolonged relaxation, pseudonormalisation, and restrictive physiology. The common denominator of these transitions is the constellation of an increase in the E/A ratio associated with a decrease in deceleration time. PATIENTS AND METHODS: Sixteen normal control subjects (6 males, 10 females, age 51.6 +/- 6.9 years) and 24 patients with mild to moderate untreated hypertension (12 males, 12 females, age 46.8 +/- 7.5 years) underwent supine blood pressure measurement with sphygmomanometry, biochemical studies, and transthoracic M-mode, 2D, and Doppler echocardiography before and after an acute saline load (7 mL kg(-1), maximum 500 mL, NaCl 0.9% within 15 min IV). RESULTS: The baseline E/A ratio was lower (0.90 +/- 0.14 vs. 1.04 +/- 0.18; P < 0.01) and the deceleration time was longer (158.8 +/- 19.4 vs. 135 +/- 8.9 ms; P < 0.01) in patients with hypertension compared with normotensive controls. However, no patient with hypertension exhibited a transmitral flow velocity pattern compatible with typical prolonged relaxation. A restrictive response to the acute saline load was observed in 12 (50%) of the hypertensive and none of the control subjects. Hypertensive patients with a restrictive response to the acute saline load had a lower baseline E velocity (54.8 +/- 8.7 cm s(-1) vs. 66 +/- 6.4 cm s(-1); P = 0.003), a lower baseline E/A ratio (0.83 +/- 0.13 vs. 0.97 +/- 0.12; P = 0.015), and a longer deceleration time (167.5 +/- 15.4 ms vs. 150 +/- 19.5; P = 0.03) than hypertensive patients without such a response. CONCLUSION: A restrictive response to an acute saline load is indicative of a limited diastolic reserve in patients with mild to moderate untreated hypertension. Further studies are required in order to evaluate the significance of such a response with regards to risk stratification and efficacy of medical treatment in this patient population.     

Increased arterial wall stiffness limits flow volume in the lower extremities in type 2 diabetic patients.

OBJECTIVE: To document an association between arterial wall stiffness and reduced flow volume in the lower-extremity arteries of diabetic patients. RESEARCH DESIGN AND METHODS: We recruited 60 consecutive type 2 diabetic patients who had no history or symptoms of peripheral arterial disease (PAD) in the lower extremities and normal ankle/brachial systolic blood pressure index at the time of the study (non-PAD group) and 20 age-matched nondiabetic subjects (control group). We used an automatic device to measure pulse wave velocity (PWV) in the lower extremities as an index of arterial wall stiffness. At the popliteal artery, we evaluated flow volume and the resistive index as an index of arterial resistance to blood flow using gated two-dimensional cine-mode phase-contrast magnetic resonance imaging. RESULTS: Consistent with previous reports, we confirmed that the non-PAD group had an abnormally higher PWV compared with that of the control group (P < 0.001). To further demonstrate decreased flow volume and abnormal flow pattern at the popliteal artery in patients with a higher degree of arterial wall stiffness, we assigned the 60 non-PAD patients to tertiles based on their levels of PWV. In the highest group, magnetic resonance angiograms of the calf and foot arteries showed decreased intravascular signal intensity, indicating the decreased arterial inflow in those arteries. The highest group was also characterized by the lowest late diastolic and total flow volumes as well as the highest resistive index among the groups. From stepwise multiple regression analysis, PWV and autonomic function were identified as independent determinants for late diastolic flow volume (r(2) = 0.300; P < 0.001). CONCLUSIONS: Arterial wall stiffness was associated with reduced arterial flow volume in the lower extremities of diabetic patients.     

Comparison of forearm plethysmography methods with brachial artery pulsed Doppler flowmetry in man

Summary. Blood flow in the forearm was evaluated using simultaneous measurements of pulsed Doppler flowmetry and strain-gauge plethysmography in 32 normal subjects and 91 patients with sustained essential hypertension. The two determinations of blood flow were strongly correlated (r = 0·58). Measurements with strain-gauge plethysmography reflected changes in blood flow velocity but were poorly correlated with changes in arterial diameter as measured by pulsed Doppler flowmetry. The latter method permits evaluation of instantaneous variations in blood flow velocity and detection of active modifications of arterial diameter.     

高血压病患者大动脉僵硬度对左室重构及功能的影响

目的探讨高血压病患者大动脉僵硬度对左室重构及功能的影响。方法应用脉搏波速度自动测量系统测量颈动脉-股动脉脉搏波速度(carotid-femoralpulsewavevelocity,CFPWV)和颈动脉-桡动脉脉搏波速度(carotid-radialpulsewavevelocity,CRPWV)分别作为反映中央弹性大动脉和外周中等肌性动脉僵硬度的指标,对36例正常人和246例高血压患者进行脉搏波速度及超声心动图检测,并根据左室质量指数(LVMI)和相对室壁厚度(RWT)将高血压患者分为左室正常和异常构型组。结果高血压左心室异常构型者CFPWV显著高于正常构型者(P<0.01),均高于正常对照组(P分别为<0.01和<0.05),CRPWV3组比较无显著差异(P>0.05)。CFPWV与RWT(r=0.133,P=0.028)、LVMI(r=0.122,P=0.044)、E/A(r=-0.313,P<0.001)及ETVI/ATVI(r=-0.345,P<0.001)呈显著相关关系,与反映收缩功能的指标无显著相关关系(P均>0.05),CRPWV与上述指标均无显著相关关系。多元逐步回归分析显示,CFPWV是影响RWT(标准化系数Beta=0.182,P=0.002)和E/A(标准化系数Beta=-0.216,P<0.001)的主要因素。结论高血压病患者大动脉僵硬度增加与左室重构及舒张功能减退密切相关。     

应用组织速度成像技术对颈总动脉壁弹性特征的研究

目的　应用组织速度成像技术对正常人和原发性高血压患者颈总动脉壁运动特点和弹性特征进行研究。方法　研究对象为 2 4例正常人和 2 4例原发性高血压合并右侧颈动脉硬化患者 ,应用 M-型超声和组织速度成像技术记录颈总动脉内径、计算可扩张度和顺应性 ,经颈总动脉内径和脉压矫正后的前壁峰值速度 (Vimax)和加速度 ACi;经心率和脉压矫正后的加速时间 (ATi)和减速时间 (DTi)。结果　正常对照组中年龄与 Vimax和 ACi呈负相关 ,Vimax、 ACi与颈总动脉壁弹性可扩张度 (DC)、颈总动脉弹性顺应性(CC)呈正相关。原发性高血压颈动脉硬化组 Vimax、 ACi与正常对照组相比明显减低 ,ATi和 DTi与正常对照组相比明显缩短。经统计学检验具有显著性差异 (P<0 .0 1)。结论　本研究显示组织速度成像技术可用来评价正常人和原发性高血压患者颈总动脉壁运动特点与弹性特征。     

The effects of left ventricular hypertrophy on the respiratory changes in transmitral Doppler flow patterns of hypertension patients

BACKGROUND: Left ventricular early diastolic fillings can be reduced by inspiration. However, the effects of left ventricular hypertrophy on such changes have not been studied before. This study was undertaken to investigate whether respiratory changes in transmitral Doppler flow were affected by left ventricular hypertrophy in hypertension patients. METHODS: Eighty-three patients (mean age 46 +/- 8 years, 49 males) with untreated essential hypertension were included in this study. Transmitral Doppler flow velocity was measured both at end-expiration and end-inspiration. Left ventricular mass was measured by M-mode echocardiography. We divided patients into two groups based on the presence of left ventricular hypertrophy or not. RESULTS: Twenty-one patients were diagnosed to have left ventricular hypertrophy. In patients without left ventricular hypertrophy, the peak early filling velocity decreased significantly (from 74 +/- 15 to 71 +/- 18 cm s(-1), P = 0.003), the peak atrial velocity increased significantly (from 65 +/- 17 to 74 +/- 15 cm s(-1), P < 0.001) and the early filling to atrial velocity ratio decreased significantly (from 1.2 +/- 0.3 to 1.1 +/- 0.3, P < 0.001) from end-expiration to end-inspiration. In patients with left ventricular hypertrophy, the parameters of transmitral Doppler flow pattern did not change during respiration. CONCLUSION: Respiratory changes in the transmitral Doppler flow velocity are blunted by left ventricular hypertrophy in hypertension patients. This phenomenon is probably contributed by the increased left ventricular wall stiffness in the left ventricular hypertrophy.     

Differentiation of abnormal relaxation pattern with aging from abnormal relaxation pattern with coronary artery disease in transmitral flow with the use of tissue Doppler imaging of the mitral annulus.

An abnormal relaxation pattern in transmitral flow velocity waveforms has been observed in older healthy subjects as well as in patients with heart disease. Accordingly, we investigated whether the hemodynamic differences between patients with coronary artery disease (CAD) with an abnormal relaxation pattern in transmitral flow (ratio of E-wave to A-wave velocities < 1.0) and healthy older subjects with an abnormal relaxation pattern can be distinguished with the use of mitral annular velocity (MAV) during early diastole. We measured MAV in the longitudinal direction of the heart during early diastole by M-mode color tissue Doppler imaging in 24 patients with atypical chest pain (defined as healthy subjects in this study) and 70 patients with CAD who underwent cardiac catheterization. In all patients a time constant of left ventricular pressure decay (tau) and the left ventricular (LV) end-systolic volume index were also measured. Twenty-one healthy subjects and 59 patients with CAD had an abnormal relaxation pattern in their transmitral flow. The age, heart rate, mean blood pressure, and ratio of E-wave to A-wave velocities were not different between the two groups. However, the tau was longer and the LV end-systolic volume index was greater in patients who had an abnormal relaxation pattern with CAD than in healthy subjects with an abnormal relaxation pattern. The MAV during early diastole was lower in the former than in the latter (5.8 +/- 1. 9 vs 9.8 +/- 1.9 cm/s, P <.001). Mitral annular velocity during early diastole by M-mode color tissue Doppler imaging can detect the differences in LV relaxation and LV systolic performance between the abnormal relaxation pattern with CAD and the physiologically abnormal relaxation pattern with aging, providing further information regarding the meaning of an LV abnormal relaxation pattern.     

超声心动图评价高血压病患者左心功能

目的运用超声心动图技术综合评价高血压病患者左室收缩功能和舒张功能。方法高血压病组56例和对照组36例,M-型和二维(2D)超声心动图检测:左房内径(LAd),舒张期室间隔厚度(IVST)和左室后壁厚度(PWT),左室舒张末期内径(LVDd),二尖瓣EF斜率,室间隔及左室后壁运动幅度,左室射血分数(EF),左室短轴缩短率(FS),每搏量(SV);脉冲多普勒(PW)检测二尖瓣口舒张早期充盈峰速度(VE),舒张晚期充盈峰速度(VA),E/A比值,等容舒张时间(IVRT)。结果高血压病患者左室壁与室间隔收缩期运动幅度普遍增强,与对照组比较P<0.01;左室收缩功能各项参数(EF、FS、SV)高于对照组(P<0.05),高血压病组左室舒张功能各参数异常,表现为VE减低,VA升高,E/A<1,IVRT延长,MV-EF斜率减慢,与对照组比较P<0.001;左房扩大(P<0.001)。结论超声心动图技术可反映高血压病患者左心结构和功能变化,为临床诊治提供客观依据。     

Tei指数评价原发性高血压病患者左室舒张功能

目的探讨Tei指数评价原发性高血压病左室不同构型的舒张功能的临床价值。方法原发性高血压病患者115例,以Ganau分类法分为4组:正常构型组36例,向心性重构组36例,向心性肥厚组31例,离心性肥厚组12例;另选择体检健康者35例为对照组。应用M型超声测量左室的舒张末期内径(LVEDD)、后壁厚度(LVPWT)、室间隔厚度(IVST);改良Simpson法测量左室射血分数(LVEF);脉冲多普勒测量二尖瓣舒张早期血流峰值流速(E)、舒张晚期血流峰值流速(A)、E峰减速时间(EDT),计算E/A;测量肺静脉血流频谱收缩期肺静脉血流峰值(PVS)、舒张早期血流峰值(PVD),计算PVS/PVD,组织多普勒测量左室Tei指数。结果高血压病组左室舒张功能均减低。正常构型组、向心性重构组、向心性肥厚组E/A1,EDT延长;离心性肥厚组E/A1,其EDT较正常构型组、向心性重构组、向心性肥厚组缩短,收缩功能减低,LVEF与对照组比较差异有统计学意义(P0.05);对照组、高血压病各组Tei指数依次增加,组间差异均有统计学意义(均P0.05);左室Tei指数与LVEF、A峰呈负相关,与IVST、LVPWT、LVEDD、RWT、LVMI、E峰、E/A呈正相关;Tei指数ROC曲线下面积为0.986,以Tei指数为0.425鉴别有无左室舒张功能不全的敏感性为97%,特异性为83%。结论 Tei指数与原发性高血压病患者左室不同构型具有良好的相关性,原发性高血压病早期Tei指数即发生改变,随舒张功能不全的加重而增高;Tei指数可作为评价鉴别二尖瓣血流"假性正常化"的参考指标之一。     

速度向量成像技术对高血压患者颈总动脉管壁运动的分析研究

目的应用速度向量成像(VVI)技术探讨高血压患者颈总动脉管壁运动特点。方法采用VVI技术测量20例高血压患者(高血压组)和20例正常人(正常对照组)颈总动脉管壁短轴切面6个壁段(前壁、前内侧壁、后内侧壁、后壁、后外侧壁、前外侧壁)的最大径向速度(Vmax)、最大切向应变(Smax)及最大切向应变率(SRmax),并进行比较。结果正常对照组颈总动脉前壁、前外侧壁、后外侧壁Vmax高于前内侧壁、后内侧壁、后壁。高血压组Vmax各壁之间差异无统计学意义(P>0.05),高血压组颈总动脉各壁Vmax(除后壁外)均小于正常对照组(P<0.05)。高血压组与正常对照组各壁间Smax、SRmax比较差异均无统计学意义(P>0.05),高血压组颈总动脉各壁段Smax、SRmax均小于正常对照组的对应壁段(P<0.05)。高血压组颈总动脉运动协调性较正常对照组差。结论 VVI技术可对高血压患者颈总动脉管壁运动的特点进行分析。     

大动脉僵硬度与高血压左室肥厚的相关性研究

目的：探讨高血压患者左室肥厚的形成与大动脉僵硬度的关系。方法：应用超声回声跟踪技术测定大动脉僵硬系数（B值）作为评价大动脉僵硬度的指标,分别对80例正常人及高血压左室肥厚患者进行相关性分析。结果：正常人和高血压患者的同年龄组口值与室间隔（IVS）及左室后壁（LVPW）厚度的比较差异有显著性（P〈0．05）,高血压各组数值均偏高。B值与高血压左室肥厚（LVH）呈正相关（P〈0．01）。结论：大动脉的僵硬度增加是导致高血压左室肥厚形成的重要原因。     

QTVI对高血压心脏病患者左心室舒张功能的评价

目的　探讨定量组织速度成像(QTVI)技术评价原发性高血压性心脏病患者左心室心肌舒张功能的价值。方法　应用QTVI获取2 5例正常人和4 7例原发性高血压心脏病患者左室长轴方向左室前壁(aw)、后壁(pw)、下壁(iw)、侧壁(lw)及前间隔(as)和后间隔(ps)的心肌多普勒速度曲线,分别比较舒张早期峰值速度(Ve)、左房收缩速度(Va)和舒张后期正向波速度(Vev)。结果　对照组的组织多普勒曲线舒张期表现为有规律的负向波e、a ,并且负向波的峰值速度Ve >Va。在e、a之间是小的舒张后期正向波ev,Vev在侧壁、前壁和后壁大于室间隔。高血压向心性肥厚组的组织多普勒曲线失去此规律,各个室壁的Ve较对照组均减小,差别显著(P <0 . 0 1)。Vev在侧壁、前壁和后壁较对照组减小也有统计学意义(P <0 .0 5 )。Va与对照组比较差异没有统计学意义(P >0 . 0 5 )。结论　QTVI定量评价高血压心脏病患者左心室心肌舒张功能具有客观、便捷等优点,为临床判断病情及预后提供有效参考。     

组织多普勒速度图评价高血压左室心肌运动

目的探讨定量组织速度成像在评价高血压左室心肌运动方面的临床价值。方法运用彩色组织多普勒速度图对55例健康者及32例高血压患者的左室各心肌节段的速度曲线进行分析,测量舒张期左室心肌的收缩期运动速度(Vs)、舒张早期的运动速度(Ve)、舒张晚期运动速度(Va),并计算Ve/Va数值。结果正常人室壁的Vs与高血压组无显著差异,Ve明显高于高血压组(P<0.001),而Va则明显低于高血压组(P<0.001),Ve/Va明显高于高血压组(P<0.001)。高血压患者的左室心肌收缩速度曲线因病史、年龄、血压控制状况不同而形态各异,舒张期曲线以E波相似文献   

双功彩色多普勒超声对原发性高血压左室肥厚肾内动脉血流的评价

目的：应用双功彩色多普勒超声观察原发性高血压继发左室肥厚患者肾内动脉血流动力学的变化。方法：利用ＡＴＬＵＭ－９及ＨＰｓｏｎｏｓ－２５００超声仪检测了同一年龄组３２例正常人和３０例原发性高血压左室肥厚患者肾内动脉（段动脉、叶间动脉）的血流参数—收缩峰速度（Ｖｓｍａｘ）、舒张期最低流速（Ｖｄｍｉｎ）、阻力指数（ＲＩ）和加速度时间（ＡＴ）。结果：原发性高血压左室肥厚肾脏的段动脉和叶间动脉的ＲＩ、ＡＴ均较正常对照组明显增高（Ｐ均＜０．０１）。Ｖｓｍａｘ和Ｖｄｍｉｎ均明显低于对照组（ｐ均＜０．０１）。结论：原发性高血压左室肥厚患者肾内动脉（段动脉、叶间动脉）的收缩期和舒张期血流均处于低流速，肾血管处于高阻力状态。     

高分辨率超声检测高血压和冠心病患者的动脉壁增厚及粥样硬化斑块

对２１例冠心病、２９例原发性高血压、２２例高血压并发冠心病及２２例正常人，作双侧颈总动脉、股动脉超声检查，探头的频率７．０ＭＨｚ，以动脉的内膜－中层厚度作为动脉壁的厚度，并检测动脉粥样硬化斑块的出现情况。结果显示各病例组所检测的指标均明显高于正常人组，高血压并发冠心病组高于高血压组和冠心病组。结论：动脉内膜－中层厚度值可反映动脉粥样硬化和高血压早期动脉病变，并可作为动脉粥样硬化晚期斑块大小的定量指标，高分辨率超声图像能为我们提供动脉壁病变的直接证据     

脉冲多普勒超声心动图对高血压病人冠脉血流储备的测定

目的　应用经胸脉冲多普勒超声心动图 (PDE)测定高血压病人的冠脉血流储备功能 (CFR)。方法　 2 0例正常人和 3 5例无并发症的轻中度原发性高血压病人经静脉注射潘生丁 ,测量用药前后左冠状动脉主干舒张期峰值速度 ,计算其比值作为冠脉血流储备指标。结果　高血压病人无论是否伴有心肌肥厚均伴有冠脉血流储备指标D/RPDV的减低 ,差异显著 (P <0 .0 1)。结论　原发性高血压病人均存在冠脉血流储备减低     

Abnormal renal haemodynamics during exercise in young patients with mild essential hypertension without treatment and during long-term propranolol therapy

The effect of exercise on renal haemodynamics was studied in young patients with mild essential hypertension: in nine untreated patients and eleven patients treated with propranolol for 19 months, and in ten normotensive healthy control subjects. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured during four consecutive periods: a pre-exercise control period, two periods with exercise loads of 450 kpm/min and 600 kpm/min, respectively, and a post-exercise control period. Comparison within groups showed a gradual fall in RPF and GFR during increasing exercise loading for both the untreated and propranolol-treated patients and the control subjects. Comparison between groups revealed no significant differences in RPF and GFR in the pre-exercise control period. For both intensities of exercise loading, RPF was signicantly lower in the untreated patients than in the control subjects, but higher than in the propranolol-treated patients. GFR in the untreated group did not differ from the level in the control group under an exercise load of 450 kpm/min, but was reduced by the heavier exercise load. GFR in the propranolol-treated patients was lower than in the untreated ones during both exercise loads. The abnormal reductions in renal haemodynamics during exercise in untreated essential hypertensive patients could be attributed to minor functional or morphological changes in the renal vascular bed not demonstrable at rest, but unmasked during exercise. The more pronounced reduction in renal haemodynamics during exercise in the propranolol-treated patients compared with the untreated hypertensives could be related to increased α-adrenergic activity compensating for the impaired cardiac response to exercise during β-adrenergic blockade.     

经颅多普勒对高血压病脑血流动力学评价

采用经颅多普勒（ＴＣＤ）超声检查技术观察一组共３０例高血压病人脑动脉血流频谱图。其中Ⅱ期高血压２１例，Ⅲ期高血压９例；与非高血压对照组比较，高血压病人脑动脉平均血流速度（Ｖｍ）显著降低（Ｐ＜０．００１），血流脉动指数（ＰＩ）明显增高（Ｐ＜０．００１），同时伴有血流频谱形态的显著异常；高血压病史愈长，脑血管并发症愈多，ＰＩ值愈高，Ｖｍ愈低。认为ＴＣＤ技术作为一种无创伤性检测手段，能较为客观地评价高血压病人脑动脉血流动力学变化，对预测与防止中风发生，具有重要的临床价值。     

多普勒组织成像对高血压左心室肥厚患者左心室舒张功能的评价

目的 应用多普勒组织成像（DTI）技术评价高血压左心室肥厚患者左心室舒张功能，并与二尖瓣血流频谱作对比。方法 研究对象为35例临床与超声诊断的高血压左心室肥厚患者（高心组）和20例正常人（对照组）。采用心尖四腔观，选取室间隔中段，左室侧壁中段，二尖瓣环-室间隔交界处、二尖瓣环一侧壁交界处为取样点，分别显示各部位组织的运动情况，并测量心肌收缩峰速度（Vs）、心肌舒张早期峰值速度（Ve）、舒张晚期峰值速度（VA）及VE与VA比值（VE/VA）。常规测量二尖瓣血流频谱，与DTI参数作对比。结果 与对照组相比，高心组室间隔中段，侧壁中段、二尖瓣环VE、VE/VA均显著下降，各部位VE/VA均与二尖瓣血流频谱E/A之间存在高度相关性；DTI对高血压左心室肥厚患者左心室舒张功能异常的诊断灵敏度高于二尖瓣血流频谱。结论 DTI技术可以定量评价高血压左心室肥厚患者的左心室舒张功能，并且比常规脉冲波多普勒二尖瓣血流参数更加敏感。     

多普勒超声心动图检测肺静脉及二尖瓣血流评价左室舒张功能

目的　探讨经胸多普勒超声心动图检测肺静脉血流频谱（ＰＶＦＰ）及二尖瓣血流频谱（ＭＶＦＰ） 的变化无创评价左室舒张功能的价值。方法　选择４０ 岁以上的无心脏疾患者３０ 例为对照组;高血压病左房不大组３０ 例;冠心病左房不大组３０ 例;高血压或冠心病左房扩大组３０ 例共１２０ 例为研究对象。使用经胸多普勒超声心动图记录肺静脉及二尖瓣血流频谱,观察各组病人肺静脉及二尖瓣血流速度的变化和左室舒张功能的关系。结果　高血压或冠心病左房不大组与对照组比较,ＭＶＦＰ 中Ｅ 峰速度减低,Ｅ 峰减速时间延长,Ａ 峰速度增高,Ｅ／Ａ 比值减低。ＰＶＦＰ中Ｓ峰速度增快,ＳＦ增大,二组之间有明显差异（ Ｐ＜ ００１） ;高血压或冠心病左房扩大组与对照组比较ＰＶＦＰ中Ｓ峰速度减低,ＳＦ减低,ＰＡ 速度增快、间期延长,ＰＡｄ ＞ Ａｄ（ Ｐ＜ ００１） ,而ＭＶＦＰ除ＥＤＴ 缩短以外,Ｅ、Ａ 峰速度、Ｅ／Ａ 比值二者近似（ Ｐ＞ ００５） 。结论　超声心动图记录肺静脉及二尖瓣血流变化能够较全面地评价左室舒张功能。