Evaluation of Cardiac Contractility by means of Q-D and D-S Time Intervals

Q-D时间是指从心电Q波开始到舒张压周期之间的时间间隔。它被认为是心肌的电作用和机械作用的时滞。D-S时间是指舒张压和收缩压之间的时间间隔。我们测量了心脏手术患者的这两个时间间隔，在正常心脏条件下，Q-D时间和D-S时间几乎为100m秒，这些时间间隔不受心率的影响。当患者处于体外循环低温心脏灌注(ECC)时，这些时间间隔明显延长2~3倍。与Q-D时间相比，D-S时间的变化更为显著。心肌的体力以力值与持续时间的乘积来评价。因此，心肌的收缩能力降低得越多，同样数量的血液在左心室排出所需的持续时间就越长。Q-D时间内的心脏做功被认为是从心房压水平到舒张压水平的势能的累积。在Q-D时间内，体循环没有外功。然而，D-S时间显然是心功能的负荷时间间隔。每搏输出量被射出，全身血压从舒张期上升到收缩期。因此，我们得出结论：D-S时间段的心肌负荷比Q-D时间段的大。

Q-D time is the time interval between the beginning of electrical Q wave in ECG and the period of diastolic pressure. It is regarded as the time lag of electrical action and mechanical action of the heart muscle. D-S time is the time interval between the period of the diastolic pressure and that of the systolic pressure. We measured both time intervals in patients undergoing the cardiac surgery.In the normal cardiac condition, Q-D time and D-S time was almost 100 m second and these time intervals did not affected by the heart rate. When the patient was under the extra corporeal cardiac perfusion (ECC) with hypothermia, these time intervals extended two or three times significantly. Changes of D-S time was more significant compared with that of Q-D time.Physical power of cardiac muscle is evaluated by multiplied value of force and duration time. Therefore the more the contractility of the heart muscle decreases, the more the duration time is needed for the ejection of the same amount of blood in the left ventricle. The cardiac work during Q-D time is regarded an accumulating the potential energy from the level of atrial pressure to that of diastolic pressure. There is no external work to the systemic circulation during Q-D time. D-S time is, however, obviously the loading time interval of the cardiac function. The stroke volume is ejected and the systemic blood pressure is increased from diastole to systole. Hence, we conclude that the load of cardiac muscle during the D-S time is heavier than that of during Q-D time.