Ramirez-Marrero Farah A, Charkoudian Nisha, Hart Emma C, Schroeder Darrell, Zhong Liu, Eisenach John H, Joyner Michael J
Department of Anesthesiology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
J Appl Physiol (1985). 2008 Nov;105(5):1448-53. doi: 10.1152/japplphysiol.90796.2008. Epub 2008 Aug 28.
Orthostatic stress such as head-up tilt (HUT) elicits a wide range of heart rate (HR) and arterial pressure (AP) responses among healthy individuals. In this study, we evaluated cardiovascular dynamics in healthy subjects with different HR responses to HUT, but without autonomic dysfunction. We measured AP (brachial artery) and HR (ECG) during 5 min of 60 degrees HUT in 76 healthy normotensive individuals. We then chose individuals on the basis of the extremes of HR responses to HUT (high = DeltaHR > or = 20 beats/min, and low = DeltaHR < or = 10 beats/min; n = 15 per group). Peak HR during HUT was 87 +/- 10 beats/min in the high and 69 +/- 14 beats/min in the low group (P < 0.05). High HR responders had lower systolic pressure at baseline (121 +/- 9 vs. 129 +/- 11 mmHg, P < 0.05) and during HUT (120 +/- 10 vs. 131 +/- 13 mmHg, P < 0.05), and higher plasma norepinephrine (NE) response to HUT (DeltaNE: 156.9 +/- 17.8 vs. 89.0 +/- 17.2 pg/ml; P < 0.05). DeltaNE during HUT was also significantly correlated with DeltaHR when all 76 subjects were included in a regression analysis (r = 0.39; P < 0.001). Pulse pressure was lower during HUT in high HR responders compared with low HR responders (45 +/- 1 vs. 55 +/- 2 mmHg, P < 0.05). High HR responders also had larger fluctuations in systolic and pulse pressure during HUT (coefficient of variation = 10.7 +/- 0.7 vs. 5.7 +/- 0.3%; 7.9 +/- 0.5 vs. 4.1 +/- 0.4%, respectively, P < 0.05). Sex distribution was different between groups (high: 5 women, 10 men; low: 10 women, 5 men). Higher HR with lower AP during HUT is consistent with normal baroreflex mechanisms of integration. Although interindividual variability appears to be a fundamental part of cardiovascular regulation, the mechanisms of these differences and the sex discrepancy requires further investigation.
诸如头高位倾斜（HUT）之类的直立位应激在健康个体中会引发广泛的心率（HR）和动脉压（AP）反应。在本研究中，我们评估了对HUT有不同HR反应但无自主神经功能障碍的健康受试者的心血管动力学。我们在76名健康的血压正常个体进行60度HUT的5分钟期间测量了AP（肱动脉）和HR（心电图）。然后，我们根据对HUT的HR反应的极值选择个体（高反应组 = ΔHR≥20次/分钟，低反应组 = ΔHR≤10次/分钟；每组n = 15）。高反应组在HUT期间的峰值HR为87±１０次/分钟，低反应组为６９±１４次/分钟（P < 0.05）。高HR反应者在基线时（121±9与129±11 mmHg，P < 0.05）和HUT期间（120±10与131±13 mmHg，P < 0.05）的收缩压较低，并且对HUT的血浆去甲肾上腺素（NE）反应较高（ΔNE：156.9±17.8与89.0±17.2 pg/ml；P < 0.05）。当将所有76名受试者纳入回归分析时，HUT期间的ΔNE也与ΔHR显著相关（r = 0.39；P < 0.001）。与低HR反应者相比，高HR反应者在HUT期间的脉压较低（45±1与55±2 mmHg，P < 0.05）。高HR反应者在HUT期间收缩压和脉压的波动也更大（变异系数分别为10.7±0.7与5.7±0.3%；7.9±0.5与4.1±0.4%，P < 0.05）。两组之间的性别分布不同（高反应组：5名女性，10名男性；低反应组：10名女性，5名男性）。HUT期间较高的HR与较低的AP与正常的压力反射整合机制一致。尽管个体间变异性似乎是心血管调节的一个基本部分，但这些差异的机制以及性别差异需要进一步研究。
