Harasawa Y, de Tombe P P, Sheriff D D, Hunter W C
Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, Baltimore, Md.
Circ Res. 1992 Aug;71(2):414-22. doi: 10.1161/01.res.71.2.414.
Myocardial oxygen consumption (MVO2) includes components for 1) mechanical energy generation, 2) activation, and 3) basal metabolism. Whereas the first two components are expected to increase in proportion with heart rate, a significant basal level of metabolism would consume oxygen even if the heart rate were zero. Contrary to this expectation, however, a previous study reported that, during unloaded beats, MVO2 per beat (which includes basal metabolism) was independent of heart rate. Accordingly, unloaded MVO2 per minute would extrapolate to zero at zero heart rate; this result is unexpected considering basal metabolism. To resolve this inconsistency, we varied heart rate over a wide range after inducing atrioventricular block in eight isolated cross-circulated canine hearts that contracted isovolumically. We examined whether a term representing rate-independent basal metabolism was needed to describe MVO2 per minute. Mechanical energy generated by the left ventricle was evaluated from the pressure-volume area, which was altered by changing isovolumic ventricular volume over at least five levels at each heart rate. Contractility, evaluated by the slope of the end-systolic pressure-volume relation, did not vary significantly with heart rate in this study. In contrast to the previous report, unloaded MVO2 per beat (i.e., MVO2 extrapolated to a pressure-volume area of zero) was not constant but fell monotonically with increases in heart rate in every heart. We considered that this trend was caused by a significant rate-independent basal level of MVO2 per minute. Multiple linear regression analysis confirmed that this rate-independent basal term differed significantly from zero in seven of the eight hearts studied.(ABSTRACT TRUNCATED AT 250 WORDS)
心肌耗氧量（MVO2）包括以下几个部分：1）机械能产生；2）激活；3）基础代谢。前两个部分预计会随着心率成比例增加，而即使心率为零，显著的基础代谢水平也会消耗氧气。然而，与这一预期相反，之前的一项研究报告称，在无负荷搏动期间，每搏MVO2（包括基础代谢）与心率无关。因此，在心率为零时，每分钟的无负荷MVO2外推至零；考虑到基础代谢，这一结果出人意料。为了解决这一矛盾，我们在八只离体交叉循环的犬心脏中诱导房室传导阻滞并使其等容收缩后，在很宽的范围内改变心率。我们研究了描述每分钟MVO2是否需要一个代表与心率无关的基础代谢的项。左心室产生的机械能通过压力-容积面积来评估，在每个心率水平上，通过至少五个水平改变等容心室容积来改变压力-容积面积。在本研究中，通过收缩末期压力-容积关系斜率评估的心肌收缩力并未随心率显著变化。与之前的报告相反，每搏无负荷MVO2（即外推至压力-容积面积为零的MVO2）并非恒定不变，而是在每颗心脏中均随心率增加而单调下降。我们认为这种趋势是由每分钟显著的与心率无关的基础MVO2水平引起的。多元线性回归分析证实，在研究的八颗心脏中的七颗中，这个与心率无关的基础项显著不为零。（摘要截断于250字）
