Shimizu Juichiro, Mohri Satoshi, Ito Haruo, Takaki Miyako, Suga Hiroyuki
Department of Physiology II, Nara Medical University, Kashihara, Nara, 634-8521, Japan.
J Physiol Sci. 2009 Jan;59(1):75-80. doi: 10.1007/s12576-008-0007-5. Epub 2008 Dec 12.
The external work (EW) efficiency of individual arrhythmic beats of the left ventricle (LV) cannot directly be obtained since LV O(2) consumption (VO(2)) of each beat cannot directly be measured under beat-to-beat varying contractile and loading conditions. We, however, have recently reported that VO(2) of each arrhythmic beat can reasonably be estimated by VO(2) = aPVA + bE(max) + c even under varying PVA and E(max). Here, PVA is the LV pressure-volume (P-V) area as a measure of the LV total mechanical energy, E(max) is the LV end-systolic elastance as an index of the LV contractility, a is a constant O(2) cost of PVA, b is a constant O(2) cost of E(max), and c is the basal metabolic VO(2) of the beat, all on a per-beat basis. Using the above formula in this study, we calculated VO(2) of the individual arrhythmic beats from their measured PVA and E(max) during electrically induced atrial fibrillation (AF) in normal canine hearts. We then calculated their LV EW efficiency by dividing their measured EW with the estimated VO(2). We found that the thus calculated EW efficiency of the arrhythmic beats had a rightward skewed distribution with a mode of 15% and a maximum of 18% around a mean of 13% on average in six hearts. This mode remained comparable to the efficiency (15%) at regular tachycardia though 22% lower than mean arrhythmic tachycardia.
由于在逐搏变化的收缩和负荷条件下无法直接测量左心室（LV）每次搏动的氧耗量（VO₂），因此无法直接获得左心室单个心律失常搏动的外在功（EW）效率。然而，我们最近报告称，即使在PVA和E(max)变化的情况下，每次心律失常搏动的VO₂也可以通过VO₂ = aPVA + bE(max) + c合理估算。这里，PVA是作为左心室总机械能指标的左心室压力-容积（P-V）面积，E(max)是作为左心室收缩性指标的左心室收缩末期弹性，a是PVA的恒定氧耗成本，b是E(max)的恒定氧耗成本，c是该搏动的基础代谢VO₂，均以每次搏动为基础。在本研究中，我们使用上述公式，根据正常犬心在电诱导心房颤动（AF）期间测得的PVA和E(max)计算了单个心律失常搏动的VO₂。然后，我们将测得的EW除以估算的VO₂来计算它们的左心室EW效率。我们发现，如此计算出的心律失常搏动的EW效率呈右偏态分布，在六只心脏中，平均模式为15%，最大值为18%，均值约为13%。尽管该模式比平均心律失常性心动过速低22%，但仍与规则性心动过速时的效率（15%）相当。
