Centre of Inflammation and Metabolism, Department of Infectious Diseases, Rigshospitalet, Section 7641, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
J Physiol. 2014 Jan 15;592(2):377-90. doi: 10.1113/jphysiol.2013.262246. Epub 2013 Nov 4.
In humans, maximal aerobic power (VO2 max ) is associated with a plateau in cardiac output (Q), but the mechanisms regulating the interplay between maximal heart rate (HRmax) and stroke volume (SV) are unclear. To evaluate the effect of tachycardia and elevations in HRmax on cardiovascular function and capacity during maximal exercise in healthy humans, 12 young male cyclists performed incremental cycling and one-legged knee-extensor exercise (KEE) to exhaustion with and without right atrial pacing to increase HR. During control cycling, Q and leg blood flow increased up to 85% of maximal workload (WLmax) and remained unchanged until exhaustion. SV initially increased, plateaued and then decreased before exhaustion (P < 0.05) despite an increase in right atrial pressure (RAP) and a tendency (P = 0.056) for a reduction in left ventricular transmural filling pressure (LVFP). Atrial pacing increased HRmax from 184 ± 2 to 206 ± 3 beats min(-1) (P < 0.05), but Q remained similar to the control condition at all intensities because of a lower SV and LVFP (P < 0.05). No differences in arterial pressure, peripheral haemodynamics, catecholamines or VO2 were observed, but pacing increased the rate pressure product and RAP (P < 0.05). Atrial pacing had a similar effect on haemodynamics during KEE, except that pacing decreased RAP. In conclusion, the human heart can be paced to a higher HR than observed during maximal exercise, suggesting that HRmax and myocardial work capacity do not limit VO2 max in healthy individuals. A limited left ventricular filling and possibly altered contractility reduce SV during atrial pacing, whereas a plateau in LVFP appears to restrict Q close to VO2 max .
在人体中，最大有氧能力（VO2 max）与心输出量（Q）的平台有关，但调节最大心率（HRmax）和每搏输出量（SV）相互作用的机制尚不清楚。为了评估心动过速和 HRmax 升高对健康人最大运动期间心血管功能和能力的影响，12 名年轻男性自行车运动员在递增式踏车运动和单腿伸膝运动（KEE）中进行了一项实验，通过右心房起搏增加 HRmax，直至力竭。在对照性踏车运动中，Q 和腿部血流量增加到最大工作负荷（WLmax）的 85%，直到力竭时仍保持不变。SV 最初增加，达到平台，然后在力竭前下降（P < 0.05），尽管右心房压（RAP）增加，左心室壁间充盈压（LVFP）有下降趋势（P = 0.056）。心房起搏使 HRmax 从 184±2 次/min 增加到 206±3 次/min（P < 0.05），但由于 SV 和 LVFP 较低（P < 0.05），Q 在所有强度下仍与对照条件相似。动脉压、外周血液动力学、儿茶酚胺或 VO2 没有差异，但起搏增加了心率血压乘积和 RAP（P < 0.05）。在 KEE 期间，心房起搏对血液动力学也有类似的影响，只是起搏降低了 RAP。结论是，人类心脏可以被起搏到比最大运动时更高的 HR，这表明 HRmax 和心肌工作能力在健康个体中不会限制 VO2 max。心房起搏时，左心室充盈受限，可能导致收缩力改变，导致 SV 下降，而 LVFP 平台似乎限制了 Q 接近 VO2 max。
