Reduced baroreflex control of heart rate during lower body negative pressure and carotid arterial wall characteristics in the elderly

本研究的目的是比较老年人和年轻男性在中枢性低血容量应激时动脉压力感受性反射对心率(HR)的控制。健康老年男性(68±1岁)和青年男性(20±0岁)因低血容量应激而接受分级下体负压(LBNP)。顺序法测定HR压力反射敏感性(BRS)的基线值在两组间无明显差异。在下体负压(~60 mm Hg)中，青年组HR的BRS减弱，而老年男性则无明显变化。下体负压时可能存在压力感受性弧功能的损害，包括压力感受器所在的血管的扩张性。为了阐明颈动脉扩张性与HR的BRS之间的关系，本研究进一步检测了颈动脉壁特征和HR的BRS。10例健康青年男性(22±1岁)和老年男性(69±1岁)各10例，超声测量颈动脉内膜中层厚度(IMT)、颈动脉管腔直径及其随动脉搏动的变化。颈动脉压平式眼压计测量血压。通过注射苯肾上腺素(动脉压升高)或硝普钠(动脉压下降)来评估HR的BRS。老年组颈动脉IMT高于青年组，而颈动脉基础顺应性低于青年组。颈动脉收缩压基线水平与年龄无关。无论是上升压力还是下降压力，老年人HR的BRS均低于年轻人。颈动脉IMT或基线顺应性与HR的BRS相关(p&lt；0.05)。这些结果表明，在老年人基础和低血容量性应激期间，IMT的增加与HR的顺应性和压力感受性反射控制的减少同时发生。

The purpose of this study was to compare arterial baroreflex control of heart rate (HR) during a central hypovolemic stress in the elderly and young males. Healthy old (68±1 y) and young (20±0 y) men underwent a graded lower body negative pressure (LBNP) for the hypovolemic stress. The baseline values of baroreflex sensitivity (BRS) of HR evaluated by the sequence method were similar in both groups. During LBNP (〜60 mm Hg), BRS of HR was attenuated in the young, however, there was no change in the old males. There is a possibility that there are some impairments of baroreflex arc function including the distensibility of vascular where baroreceptors are in the old during LBNP.To delineate the relationship between the distensibility of carotid artery and BRS of HR, the next step of this study was carried out to examine both carotid arterial wall characteristics and BRS of HR. Ten each of healthy young (22±1 y) and old (69±1 y) men underwent to measure ultrasonographically the carotid intima-media thickness (IMT), carotid arterial lumen diameter and its change with arterial pulse. Blood pressure (BP) was measured with an applanation tonometry at the carotid artery. BRS of HR was evaluated by a bolus injection of phenylephrine (rising arterial pressure) or sodium nitroprusside (falling arterial pressure). The carotid IMT was higher in the old than in the young, whereas, baseline compliance of the carotid artery was less in the old than the young. No age-related difference was detected in the baseline level of carotid systolic blood pressure. The BRS of HR was less in the old compared to the young during both rising and falling pressures. The IMT or the baseline compliance of carotid artery was related to BRS of HR (p<0.05). These results suggest that an increase in IMT occurs in concurrence with a reduction of compliance and the baroreflex control of HR during baseline and hypovolemic stress in the elderly.