心脏前负荷减低对主动脉压及主动脉扩增指数的影响

Effect of decreased cardiac preload on central blood pressure and aortic augmentation index

目的了解心脏前负荷减低对中心动脉压及主动脉扩增指数的影响。方法10例健康志愿者,行下肢负压(LB-NP)抽吸造成不同程度前负荷减低。采用超声心动图检测心输出量的变化;采用中心动脉压力分析系统(SphymoCor)检测桡动脉压力波形,经平均转换功能形成中心动脉压力波形。结果①随着下肢负压的加大,上腔静脉血流进行性减低,在-30mmHg阶段,S波减低22.4%,VTIs+d减低了15.8%,同时SV减少24.7%,CO减少18.7%;②中心动脉收缩压(CSBP)除在-30mmHg阶段轻度下降外,在-10及-20mmHg阶段没有明显改变,中心动脉舒张压(CDBP)在各个负压阶段没有明显改变;③主动脉压力波P1在各个负压阶段均明显下降,在-30mmHg阶段,P1减少了19.6%[(28.2±5.02)mmHgvs.(22.65±3.08)mmHg,P<0.01],而总外周阻力(TPR)在各负压阶段均较基础阶段明显升高,在-30mmHg阶段升高21.3%[(16.0±2.9)(mmHg.min)/Lvs.(20.3±3.4)(mmHg.min)/L,P<0.001]。主动脉扩增指数(AI)无明显改变。结论前负荷减低使中心主动脉压及主动脉压力波P1降低,同时使TPR升高,由于TPR的升高抵消了P1的降低,因而AI保持不变。

Objective To investigate the effect of decreased cardiac preload on central blood pressure and central aortic augmentation index （CAI）. Methods Ten healthy normotensive men aged 27 to 51 were studied. They were placed in a standard lower body negative pressure （LBNP） chamber to induce different degrees of LBNP. Hemodynamic and echocardiographic measurements were made at each stage of LBNP and baseline. A SphygmoCor tonometry system was used to obtain the radial pulse waveform. Aortic pressure was derived, via a validated transfer function, from radial pressure, and used to estimate cAI and central systolic blood pressure （cSBP）. Results （1） There was a progressive decrease in the SVC S wave and VTIs＋ d with increased LBNP with a maximum change of 0.21±0.03 m/s （22.4 % change） and 2.8±2.34 cm （15.8 % change） at 30 mmHg LBNP （ P〈0. 001）, respectively. This reduction in preload was associated with a progressive decrease in SV （by 24.4% at 30 mmHg, P〈0. 001） and decrease in CO （by 18.7 at 30 mmHg LBNP, P〈0.00l）. （2） LBNP decreased CSBP （by 3.7 mmHg at 30 mmHg LBNP, P〈0.01）, but had no significant change in MAP and CDBP. （3） Reduced cardiac output by LBNP decreased the P1 of aortic pressure waveform [（28.2 ±5.02） mmHg vs. （22.65±3.08） mmHg, P〈0.01] and increased the peripheral resistance [（16.0±2.9） （mmHg·min）/L vs. （20.3±3.4） （mmHg·min）/L, P〈0. 001]. CAI had no significant change at the whole LBNP stages. Conclusion Decreased preload decreased central blood pressure and P1, but increased peripheral resistance. AI remained unchanged because TPR increase offset decrease of P1.