Shi X, Foresman B H, Raven P B
Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth 76107, USA.
Am J Physiol. 1997 Mar;272(3 Pt 2):H1359-63. doi: 10.1152/ajpheart.1997.272.3.H1359.
Seven healthy volunteer men participated in an experiment involving lower body positive pressure (LBPP) of 30 Torr and acute volume expansions of 5-6% (VE-I) and 9-10% (VE-II) of their total blood volume (TBV) to differentiate the effect of increased intramuscular pressure and central venous pressure (CVP) on the maximal gain (Gmax) of the carotid baroreflex. During each experimental condition, the heart rate (HR), mean arterial pressure (MAP; intraradial artery or Finapres), and CVP (at the 3rd-4th intercostal space) were monitored continuously. Gmax was derived from the logistic modeling of the HR and MAP responses to ramped changes in carotid sinus transmural pressure using a protocol of pulsatile changes in neck chamber pressure from +40 to -65 Torr. The increase in CVP during +30-Torr LBPP was 1.5 mmHg (P < 0.05) and was similar to that observed during VE-I (1.7 mmHg, P > 0.05). The Gmax of the carotid baroreflex of HR and MAP was significantly decreased during LBPP by -0.145 +/- 0.039 beats x min(-1) x mmHg(-1) (38%) and -0.071 +/- 0.013 mmHg/mmHg (25%), respectively; however, VE-I did not affect Gmax. During VE-II, CVP was significantly greater than that elicited by LBPP, and the Gmax of the carotid baroreflex of the HR and MAP responses was significantly reduced. We conclude that carotid baroreflex responsiveness was selectively inhibited by increasing intramuscular pressure, possibly resulting in an activation of the intramuscular mechanoreceptors during LBPP. Furthermore, it would appear that the inhibition of the carotid baroreflex, via cardiopulmonary baroreceptor loading (increased CVP), occurred when a threshold pressure (CVP) was achieved.
七名健康男性志愿者参与了一项实验，该实验涉及30托的下半身正压（LBPP）以及相当于其总血容量（TBV）5 - 6%（VE - I）和9 - 10%（VE - II）的急性血容量扩充，以区分肌肉内压力和中心静脉压（CVP）升高对颈动脉压力反射最大增益（Gmax）的影响。在每种实验条件下，持续监测心率（HR）、平均动脉压（MAP；桡动脉内或Finapres测量）以及CVP（在第3 - 4肋间间隙）。Gmax通过对颈动脉窦跨壁压力的斜坡变化引起的HR和MAP反应进行逻辑建模得出，采用颈部腔室压力从 +40到 -65托的脉动变化方案。在30托LBPP期间CVP升高1.5 mmHg（P < 0.05），与VE - I期间观察到的升高相似（1.7 mmHg，P > 0.05）。在LBPP期间，HR和MAP的颈动脉压力反射Gmax分别显著降低 -0.145 ± 0.039次/分钟×mmHg⁻¹（38%）和 -0.071 ± 0.013 mmHg/mmHg（25%）；然而，VE - I并未影响Gmax。在VE - II期间，CVP显著高于LBPP引起的CVP，HR和MAP反应的颈动脉压力反射Gmax显著降低。我们得出结论，增加肌肉内压力会选择性抑制颈动脉压力反射反应性，这可能导致LBPP期间肌肉内机械感受器的激活。此外，当达到阈值压力（CVP）时，似乎会通过心肺压力感受器负荷增加（CVP升高）抑制颈动脉压力反射。
