Determination of Cardiac Output By Equating Venous Return Curves With Cardiac Response Curves ^(1){ }^{1} 通过将静脉回流曲线与心脏反应曲线 ^(1){ }^{1} 相等来确定心输出量
ARTHUR C. GUYTON 亚瑟·盖顿From the Department of Physiology and Biophysics, School of Medicine, Universily of Mississippi, University, Mississippi 来自密西西比大学医学院生理学和生物物理学系
The CONCEPT that the heart responds with increasing cardiac output when there occurs increasing venous return was popularized by Starling and, indeed, has come to be known as Starling’s law. There are many different forms in which Starling’s law can be expressed, including the relationship of cardiac output to right atrial pressure, the relationship of cardiac output to the degree of distention of the right ventricle at the end of diastole, the relationship of cardiac work to right atrial pressure or right ventricular distention, the relationship of left ventricular work to right atrial pressure or right ventricular distention, etc. For the determination of cardiac output, the form of Starling’s law which will be used in the present discussion is the relationship of cardiac output to mean right atrial pressure, and this type of cruve will be called the “cardiac response curve” to right atrial pressure. 当静脉回流增加时，心脏会随着心输出量的增加而做出反应，这一概念由 Starling 推广，实际上，它被称为 Starling 定律。斯塔林定律可以以许多不同的形式表达，包括心输出量与右心房压的关系，心输出量与舒张末期右心室扩张程度的关系，心脏功与右心房压或右心室膨胀的关系，左心室功与右心房压或右心室膨胀的关系， 等。对于心输出量的测定，本讨论中将使用的 Starling 定律的形式是心输出量与平均右心房压的关系，这种类型的 cruve 将称为右心房压的“心脏反应曲线”。
It is well known that many factors in the peripheral circulatory system combine together to determine the rate of venous return to the heart. These include the quantity of blood available, the degree of vascular resistance in various parts of the peripheral circulatory system, and the back pressure from the right atrium. It is with these factors that this paper is especially concerned, and it is hoped that this presentation will demonstrate how cardiac output is determined by equating the peripheral circulatory factors with the cardiac response curves. 众所周知，外周循环系统中的许多因素共同决定了静脉返回心脏的速度。这些包括可用血液量、外周循环系统各个部位的血管阻力程度以及来自右心房的背压。本文特别关注这些因素，希望本演讲能够展示如何通过将外周循环因素与心脏反应曲线等同来确定心输出量。
Cardiac Response Curves Under Different Conditions 不同条件下的心脏反应曲线
It is very difficult to determine cardiac response curves in the intact animal, for changing the right atrial pressure or cardiac output from normal results almost immediately in tremendous compensatory activity tending to correct these abnormal conditions. Nevertheless, by the technique of administering massive transfusions very rapidly and making measurements before complete readjustments can occur, approximate cardiac response curves have been obtained in this laboratory as illustrated in figure 1 (1). The central curve of figure 1 is approximately the response curve of the heart of an average-size dog whose vasomotor reflexes have been completely abrogated by administration of total spinal anesthesia, normal blood pressure being maintained by continuous infusion of small quantities of epinephrine. The first curve of figure I is approximately the response curve of a dog during generalized sympathetic stimulation or during continuous infusion of epinephrine. Finally, the lower response curve of figure 1 is approximately that which occurs in a dog with a moderately damaged myocardium. 很难确定完整动物的心脏反应曲线，因为在巨大的代偿活动中，右心房压或心输出量几乎立即从正常结果改变，以纠正这些异常情况。然而，通过非常快速地进行大量输血并在完全重新调整之前进行测量的技术，在该实验室中已经获得了近似的心脏反应曲线，如图 1 （1） 所示。图 1 的中心曲线大约是一只中等大小的狗心脏的反应曲线，其血管舒缩反射已通过全脊髓麻醉完全消除，通过持续输注少量肾上腺素来维持正常血压。图 I 的第一条曲线大约是狗在广泛交感神经刺激或持续输注肾上腺素期间的反应曲线。最后，图 1 的下响应曲线大约是心肌中度受损的狗出现的曲线。
The various factors which affect the cardiac response curve have been adequately reviewed many times throughout the past fifty years, and especially has 在过去的 50 年里，影响心脏反应曲线的各种因素已经被充分审查了很多次，尤其是
Sarnoff emphasized in the present symposium the variability of different types of Starling’s curves under various conditions. Suffice it to say that the following and many other factors can change the cardiac response curve from beat to beat and from time to time: 1 ) the phase of respiration at onset of cardiac contraction; 2) the interval of time elapsing between two successive heart beats; 3) the degree of sympathetic stimulation; 4) the effect of many drugs on the heart, such as digitalis, epinephrine, cholinergic drugs etc.; 5) myocardial damage; 6) cardiac fatigue; 7) the degree of oxygenation of the blood, etc. However, when the heart is operating under conditions of light respiration, constant degree of sympathetic stimulation, and with a constant source of nutrition, the cardiac response curve remains relatively constant from beat to beat. Sarnoff 在本研讨会上强调了不同类型斯塔林曲线在各种条件下的变化性。可以说，以下因素和许多其他因素可以改变心脏反应曲线，每次心跳和不时变化： 1 ） 心脏收缩开始时的呼吸阶段;2） 两次连续心跳之间经过的时间间隔;3） 交感神经刺激的程度;4）许多药物对心脏的影响，如洋地黄、肾上腺素、胆碱能药物等;5） 心肌损伤;6） 心脏疲劳;7） 血液的氧合程度等。然而，当心脏在轻呼吸、恒定程度的交感神经刺激和恒定的营养来源条件下运作时，心脏反应曲线在每次心跳中保持相对恒定。
Venous Return Curves 静脉回流曲线
The factors affecting venous return are even more elusive and more difficult to study than are the factors which determine the cardiac response curve. However, figure 2 illustrates venous return curves obtained under relatively well-controlled conditions-namely, in a recently dead dog with a pump replacing the heart. It will be observed from these curves that there are two major pressure factors which determine the quantity of blood which returns to the heart from the peripheral circulatory system. These are the right atrial pressure and the mean circulatory filling pressure. It is quite obvious that the greater the right atrial pressure, the greater is the back pressure in the veins preventing the return of blood to the heart. On the other hand, the principle of mean circulatory filling pressure is not yet well established in physiological circles, and this needs additional explanation. The term, mean circulatory filling pressure, means the mean integrated filling pressure throughout the circulatory system when one appropriately weights the volumes and degrees of elasticity of the different portions of the circulatory system. This mean circulatory filling pressure in the normal dog averages 6.3mm.Hg(2,3)6.3 \mathrm{~mm} . \mathrm{Hg}(2,3) and can be measured by momentarily stopping the pumping of blood by the heart and allowing the pressures throughout the circulatory system to come to equilibrium. The pressure measured when all blood flow has stopped has also been called ‘static blood pressure’ for obvious reasons. With this concept of mean circulatory filling pressure in mind 影响静脉回流的因素比决定心脏反应曲线的因素更难以捉摸，也更难研究。然而，图 2 说明了在相对控制良好的条件下获得的静脉回流曲线，即在最近死去的狗中，用泵替换心脏。从这些曲线中可以观察到，有两个主要的压力因素决定了从外周循环系统返回心脏的血液量。这些是右心房压力和平均循环充盈压。很明显，右心房压越大，静脉中的背压就越大，阻止血液回流到心脏。另一方面，平均循环充盈压的原理在生理学界尚未完全确立，这需要额外的解释。术语平均循环充盈压力是指当适当加权循环系统不同部分的体积和弹性度时，整个循环系统的平均综合充盈压力。正常狗的平均循环充盈压是 6.3mm.Hg(2,3)6.3 \mathrm{~mm} . \mathrm{Hg}(2,3) 平均值，可以通过暂时停止心脏泵血并让整个循环系统的压力达到平衡来测量。出于显而易见的原因，当所有血流停止时测得的压力也被称为“静态血压”。考虑到平均循环充盈压力的概念
Fig. 1. Cardiac response curves to right atrial pressure with the heart under different conditions. 图 1.在不同条件下心脏对右心房压的反应曲线。
Fig. 2. Venous return curves illustrating the effect of right atrial pressure on venous return when the mean circulatory filling pressure is maintained at different levels. 图 2.静脉回流曲线说明了当平均循环充盈压维持在不同水平时，右心房压力对静脉回流的影响。
the effect of the various factors on the venous return curve can be explained as follows: 各种因素对静脉回流曲线的影响可以解释如下：
Effect of Right Atrial Pressure on Venous Return. The curves of figure 2 were obtained by varying the right atrial pressure and the mean circulatory filling pressure. In place of the heart a perfusion pump was connected from the right atrium to the aorta, and the level of right atrial pressure was varied by increasing or decreasing the minute capacity of the pump. On the other hand, the mean circulatory filling pressure was varied by increasing or decreasing the total quantity of blood in the circulatory system. It will be noted that for each of the four curves of figure 2 the mean circulatory filling pressure was maintained at constant levels of 10.6 , 8.4,6.98.4,6.9 and 4.7mm.Hg4.7 \mathrm{~mm} . \mathrm{Hg}, respectively. 右心房压力对静脉回流的影响。图 2 的曲线是通过改变右心房压和平均循环充盈压获得的。从右心房到主动脉连接了一个灌注泵来代替心脏，右心房压力的水平通过增加或减少泵的微小容量来改变。另一方面，平均循环充盈压通过增加或减少循环系统中的血液总量来变化。需要注意的是，对于图 2 的四条曲线中的每条曲线，平均循环充盈压力分别保持在 10.6 和 8.4,6.98.4,6.94.7mm.Hg4.7 \mathrm{~mm} . \mathrm{Hg} 的恒定水平。
Observing the uppermost curve of figure 2, it is immediately obvious that when the right atrial pressure rose to a value of 10.6mm.Hg10.6 \mathrm{~mm} . \mathrm{Hg}, which was equal to the mean circulatory filling pressure, the cardiac output was zero. In other words, as the right atrial pressure approaches the mean circulatory filling pressure the cardiac output approaches zero. Consequently, the mean circulatory filling pressure constitutes the upper limit to which the right atrial pressure can rise. 观察图 2 的最上部曲线，很明显，当右心房压力上升到 10.6mm.Hg10.6 \mathrm{~mm} . \mathrm{Hg} 等于平均循环充盈压 的值时，心输出量为零。换句话说，当右心房压力接近平均循环充盈压时，心输出量接近零。因此，平均循环充盈压构成了右心房压力可以上升到的上限。
Observing once more the upper curve of figure 2, it will be noted that, as the right atrial pressure falls below the mean circulatory filling pressure, blood flows from the peripheral vessels which have a mean pressure higher than the right atrial pressure toward the right atrium, and the rate of flow into the right atrium continues to increase as the right atrial pressure falls progressively more and more below the mean circulatory filling pressure. 再次观察图 2 的上部曲线，可以注意到，当右心房压力低于平均循环充盈压时，血液从平均压力高于右心房压力的外周血管流向右心房，并且随着右心房压力逐渐下降到平均循环充盈压以入右心房的流速继续增加。
Effect of vein collapse on venous return. After the right atrial pressure falls below zero mm.Hg\mathrm{mm} . \mathrm{Hg}, the return of blood to the heart does not continue to increase, as is illustrated in figure 2. On directly observing the major veins entering the thorax, one notes that these vessels suddenly collapse as the right atrial pressure falls below zero. It has been well documented that such collapse causes the pressure in the veins where they first enter the chest cavity to remain approximately zero mm.Hg\mathrm{mm} . \mathrm{Hg} regardless of how much negative the pressure becomes in the right atrium (4,5)(4,5). Therefore, decreasing right atrial pressure below zero mm.Hg\mathrm{mm} . \mathrm{Hg}, in general, does not continue to increase the venous return to the heart. 静脉塌陷对静脉回流的影响。右心房压降至零 mm.Hg\mathrm{mm} . \mathrm{Hg} 以下后，血液回流到心脏的量不会继续增加，如图 2 所示。在直接观察进入胸腔的主要静脉时，人们注意到当右心房压力降至零以下时，这些血管会突然塌陷。有充分的证据表明，这种塌陷会导致它们最初进入胸腔的静脉中的压力保持接近零 mm.Hg\mathrm{mm} . \mathrm{Hg} ，无论右心房中的压力变得多少 (4,5)(4,5) 负值。因此，将右心房压降低到零 mm.Hg\mathrm{mm} . \mathrm{Hg} 以下 ，一般来说，不会继续增加静脉回流到心脏。
Effect of Mean Circulatory Filling Pressure on Venous Return. If the vessels of the peripheral circulatory system are well filled with blood, this causes the mean circulatory filling pressure to rise. The increased pressures in the peripheral vessels in turn cause greater tendency for the blood to flow toward the low pressure area of the right atrium. Therefore, for any given right atrial pressure the greater the mean circulatory filling pressure, the greater the venous return should be. Thus in figure 2 it is noted that for each level of right atrial pressure the venous return increases almost directly in proportion with the level of mean circulatory filling pressure. 平均循环充盈压对静脉回流的影响。如果外周循环系统的血管充满血液，这会导致平均循环充盈压升高。外周血管压力增加反过来导致血液更倾向于流向右心房的低压区域。因此，对于任何给定的右心房压，平均循环充盈压越大，静脉回流应该越大。因此，在图 2 中指出，对于每个右心房压力水平，静脉回流几乎与平均循环充盈压水平成正比增加。
Pressure gradient for venous return. From the above discussions and from figure 2 it can be seen that right atrial pressure opposes the return of blood to the heart while the mean circulatory filling pressure promotes the return of blood to the heart, though as right atrial pressure rises to approach the mean circulatory filling pressure the return of blood to the heart approaches zero. It can be shown mathematically that, provided the peripheral resistances remain absolutely constant, the momentary rate of venous return will be proportional to the mean circulatory filling pressure minus the right atrial pressure. This difference between mean circulatory filling 静脉回流的压力梯度。从上述讨论和图 2 中可以看出，右心房压阻碍血液返回心脏，而平均循环充盈压促进血液返回心脏，尽管当右心房压上升到接近平均循环充盈压时，血液返回心脏接近零。数学上可以表明，如果外周阻力保持绝对恒定，瞬时静脉回流率将与平均循环充盈压减去右心房压成正比。平均循环充盈
pressure and right atrial pressure can be called the pressure gradient of venous flow. However, negative right atrial pressures must be considered simply as zero pressure because of the collapse factor as discussed above. 压力和右心房压可称为静脉血流的压力梯度。然而，由于上述塌陷因子，必须简单地将右心房负压视为零压力。
Figure 3 illustrates an experiment in a normal dog which has received a very large and rapidly administered transfusion of whole blood (1). Following this transfusion the heart was stopped approximately every 2 minutes by electrical fibrillation; then the mean circulatory filling pressure was measured within a few seconds; and thereafter the heart was electrically defibrillated. By measuring right atrial pressure and cardiac output simultaneously it was possible to plot the pressure gradient of venous flow (MCFP-RAP) against cardiac output (venous return) as illustrated in the figure. This figure illustrates that the venous return and cardiac output are approximately proportional to the pressure gradient of venous flow, though there is an inflection in the curve. This inflection is to be expected, for one would expect the peripheral resistances to decrease as the filling pressures throughout the peripheral vessels increase and consequently distend the respective vessels. Thus this experiment and many other similar experiments have correlated beautifully with the concepts presented above (6). 图 3 说明了在一只正常狗身上进行的实验，该狗接受了非常大且快速的全血输注 （1）。输血后，大约每 2 分钟通过电颤动停止心脏跳动;然后在几秒钟内测量平均循环充盈压力;此后，心脏被电除颤。通过同时测量右心房压和心输出量，可以绘制静脉血流压力梯度 （MCFP-RAP） 与心输出量（静脉回流）的关系，如图所示。该图表明，静脉回流和心输出量与静脉血流的压力梯度大致成正比，尽管曲线存在拐点。这种拐点是意料之中的，因为人们会预期随着整个外周血管的充盈压力增加，外围阻力会降低，从而导致相应的血管膨胀。因此，这个实验和许多其他类似的实验与上面提出的概念完美地相关 （6）。
Effect of Peripheral Resistances on Venous Return. The effect of the peripheral resistances on venous return is the most difficult factor relating to venous return to understand and to assess, and it will be impossible to give a thorough discussion of this factor at the present time. In general, when there occurs an increase in vascular resistance between the major blood reservoirs and the right atrium, this decreases the cardiac output tremendously; on the other hand, when there occurs an increase in resistance between the left ventricle and the major blood reservoirs, this affects the left ventricular blood pressure tremendously but affects the venous return to only a slight extent. This latter effect is illustrated in figure 4. The experiment of figure 4 was performed on a freshly dead dog by the method described for figure 2 (1). The peripheral resistance was changed from one curve to the next by injecting into the arterial system large quantities of 250 micron glass beads which plugged the minute arteries. It is obvious from figure 4 that even though the total peripheral resistance increased 2.6 times, the maximal venous return decreased by only 10 per cent. This is approximately the decrease in venous return which one would mathematically predict, for there occurs as a consequence of the increased resistance in the small vessels a small amount of pooling of blood in the elastic arterial blood reservoir, thereby decreasing to a slight extent the effective filling pressures of the vessels in the venous side of the circulatory system and thus decreasing venous return slightly. 外周阻力对静脉回流的影响。外周阻力对静脉回流的影响是与静脉回流相关的最难理解和评估的因素，目前不可能对这一因素进行深入讨论。一般来说，当主要血库和右心房之间的血管阻力增加时，这会大大降低心输出量;另一方面，当左心室和主要储血器之间的阻力增加时，这会极大地影响左心室血压，但对静脉回流的影响很小。后一种效果如图 4 所示。图 4 的实验是通过图 2 （1） 中描述的方法对一只刚死去的狗进行的。通过将大量 250 微米玻璃珠注射到动脉系统中，堵塞微小动脉，外周阻力从一条曲线变为另一曲线。从图 4 中可以明显看出，尽管总外周阻力增加了 2.6 倍，但最大静脉回流仅下降了 10%。这大约是人们可以从数学上预测的静脉回流的减少，因为由于小血管阻力的增加，弹性动脉血库中的少量血液淤积，从而在一定程度上降低了循环系统静脉侧血管的有效充盈压力，从而略微降低了静脉回流。
Fig. 3. Effect of the pressure gradient for venous return (MCFP-RAP) on cardiac output 图 3.静脉回流压力梯度 （MCFP-RAP） 对心输出量的影响
Fig. 4. Effect of increasing peripheral resistance on venous return when the peripheral resistance is increased by occluding the small arteries with 250 micron glass beads. 图 4.当用 250 微米玻璃珠封闭小动脉来增加外周阻力时，增加外周阻力对静脉回流的影响。
An additional experiment was performed in the same manner as that illustrated in figure 4 except that the increasing resistance was applied by progressive occlusion of the veins entering the right atrium. In this experiment the total peripheral resistance increased only about 10 per cent, but the venous return decreased four times. 以与图 4 所示相同的方式进行了一项额外的实验，只是通过进入右心房的静脉的逐渐闭塞施加了增加的阻力。在这个实验中，总外周阻力仅增加了约 10%，但静脉回流下降了四倍。
Thus both mathematically and experimentally it can be shown that changes in vascular resistance which occur near the right atrial end of the peripheral circulatory system greatly affect venous return to the heart, while changes in vascular resistance at progressively greater and greater distances away from the right atrium exert progressively less and less effect on venous return until finally resistance changes in the arterial tree affect venous return only slightly. 因此，从数学和实验上都可以表明，发生在外周循环系统右心房端附近的血管阻力变化极大地影响了静脉回流到心脏，而在远离右心房的距离越来越远的地方，血管阻力的变化对静脉回流的影响越来越小，直到最后动脉树的阻力变化对静脉回流的影响很小。
A Formula for Expressing Venous Return. Venous return may be expressed by the formula 表达静脉回流的公式。静脉回流可以用公式表示
V.R.=(f(MCFP)*f(D))/(v)*(MCFP-RAP)*C\mathrm{V} . \mathrm{R} .=\frac{f(\mathrm{MCFP}) \cdot f(D)}{v} \cdot(\mathrm{MCFP}-\mathrm{RAP}) \cdot C
which may be explained as follows: the factor, CC, is simply a constant for mathematically relating the other factors. The factor (MCFP-RAP) is the pressure gradient for venous flow as discussed above, illustrating that the greater the difference between the mean circulatory filling pressure and right atrial pressure, the greater 可以解释如下：因子 CC ，只是数学上关联其他因子的常数。因子 （MCFP-RAP） 是如上所述的静脉血流压力梯度，表明平均循环充盈压和右心房压之间的差异越大，
will be the venous return. The factor, (f(MCFP)*f(D))/(v)\frac{f(\mathrm{MCFP}) \cdot f(D)}{v}, is an expression for determining 将是静脉回流。因子 (f(MCFP)*f(D))/(v)\frac{f(\mathrm{MCFP}) \cdot f(D)}{v} ， 是用于确定
the conductivity of the peripheral circulatory system for venous return, and this factor is the reciprocal of the resistances which resist the return of blood to the heart. The function, ff (MCFP), illustrates that the greater the mean circulatory filling pressure, the greater will be individual filling pressures in the different vessels and the greater will these vessels be distended; as the mean circulatory filling pressure increases, this factor alone should decrease the resistance to venous flow and increase the return of blood to the heart. Measurements thus far, however, have indicated that this factor is not as important as might have been expected. The function, f(D)f(D), is a function of the different dimensions of the peripheral circulatory system, illustrating that the greater these dimensions, the greater will be the venous return. This factor is so complicated that it is doubtful that it will ever be completely understood, though the general principles as discussed above relating it to venous return are not necessarily difficult. The expression, vv, illustrates that the greater the viscosity of the blood, the less will be the venous return. 外周循环系统对静脉回流的电导率，这个因素是抵抗血液回流到心脏的阻力的倒数。函数 ff （MCFP） 表明，平均循环充盈压力越大，不同血管中的单个充盈压力就越大，这些血管的膨胀就越大;随着平均循环充盈压的增加，仅此因素应降低对静脉流动的阻力并增加血液流向心脏的回流。然而，迄今为止的测量表明，这个因素并不像预期的那么重要。函数 f(D)f(D) 是外周循环系统不同维度的函数，说明这些维度越大，静脉回流就越大。这个因素非常复杂，以至于很难完全理解它，尽管上面讨论的将其与静脉回流相关的一般原则不一定困难。表达式 vv ， 说明了血液的粘度越大，静脉回流就越少。
Equating Venous Return Curves With Cardiac Response Curves 将静脉回流曲线与心脏反应曲线等同
Figure 5 illustrates a number of different types of venous return curves at different peripheral resistances and at different mean circulatory filling pressures. On the same graph are shown the three cardiac response curves illustrated in figure 1. If a normal-size dog is operating with approximately a normal cardiac response curve as illustrated by the heavy response curve of figure 5 and at the same time the various peripheral factors are approximately normal so that his venous return curve is that illustrated by the heavy venous return curve, it is obvious that these two curves equate with each other at point AA, at which point the cardiac output is approximately 1525cc//min1525 \mathrm{cc} / \mathrm{min}., and the right atrial pressure is approximately zero. The 图 5 说明了在不同外周阻力和不同平均循环充盈压力下许多不同类型的静脉回流曲线。在同一张图上显示了图 1 中所示的三条心脏反应曲线。如果一只正常大小的狗以大致正常的心脏反应曲线进行作，如图 5 的重反应曲线所示，同时各种外周因素大致正常，因此他的静脉回流曲线是重静脉回流曲线所说明的曲线，很明显，这两条曲线在点 AA 上彼此相等， 此时心输出量约为 1525cc//min1525 \mathrm{cc} / \mathrm{min} .，右心房压力约为 0。这
heavy points on the graph illustrate the different possible equating points for respective venous return and cardiac response curves. 图上的粗点说明了各自静脉回流和心脏反应曲线的不同可能相等点。
Obviously, except under momentary conditions the venous return and the cardiac output must be equal. For instance, if the myocardium is damaged, the cardiac response curve under which the heart is momentarily operating would be similar to the lower cardiac response curve, and, if the mean circulatory filling pressure is greatly increased, then the venous return curve would be affected in some manner similar to that illustrated by the venous return curve to the right in figure 5. The only point on these two curves at which the venous return and cardiac output are equal is at point BB, at which the cardiac output is approximately 2050cc//min2050 \mathrm{cc} / \mathrm{min}., and the right atrial pressure is 6.2mm.Hg6.2 \mathrm{~mm} . \mathrm{Hg}. 显然，除非在瞬时情况下，静脉回流和心输出量必须相等。例如，如果心肌受损，心脏瞬时运转的心脏反应曲线将类似于较低的心脏反应曲线，并且，如果平均循环充盈压大大增加，那么静脉回流曲线将以某种方式受到影响，类似于图 5 中右侧的静脉回流曲线所示。在这两条曲线上，静脉回流量和心输出量相等的唯一点是点 BB ，此时心输出量约为 2050cc//min2050 \mathrm{cc} / \mathrm{min} ，右心房压力为 6.2mm.Hg6.2 \mathrm{~mm} . \mathrm{Hg} 。
It will have been noted in the above discussion that right atrial pressure is a common factor in both the cardiac response curve and in the venous return curve. When these curves are equated with each other, the right atrial pressure becomes an exact value at the same time that the equilibrium value of venous return and 在上面的讨论中已经注意到，右心房压是心脏反应曲线和静脉回流曲线中的一个公共因素。当这些曲线彼此相等时，右心房压成为精确值，同时静脉回流和
Fig. 5. Equilibration of various venous return curves with different cardiac response curves. 图 5.不同心脏反应曲线的各种静脉回流曲线的平衡。
cardiac output becomes an exact value. Though it is impossible to discuss the mathematics at the present time, it can be shown that right atrial pressure is not one of the primary determinants of cardiac output but, instead, is itself determined simultaneously along with cardiac output. The factors which determine cardiac output and right atrial pressure simultaneously are, first, the shape of the cardiac response curve under which the heart is momentarily operating and, second, the peripheral circulatory factors which affect venous return, these including the mean circulatory filling pressure, the momentary dimensions of the peripheral system, and the viscosity of the blood. 心输出量变为精确值。虽然目前无法讨论数学，但可以证明右心房压不是心输出量的主要决定因素之一，而是与心输出量同时决定。同时决定心输出量和右心房压的因素是，首先，心脏瞬时运行的心脏反应曲线的形状，其次，影响静脉回流的外周循环因素，这些因素包括平均循环充盈压、外周系统的瞬时尺寸和血液的粘度。
Summary 总结
The factors which affect the ability of the heart to respond with increasing cardiac output as the right atrial pressure rises have been discussed briefly. On the other hand, the less popularized factors which affect venous return of blood to the heart have been discussed at greater length, it having been pointed out that right atrial pressure opposes return of blood to the heart, whereas the mean circulatory filling pressure promotes return of blood to the heart. The difference between mean circulatory filling pressure and right atrial pressure represents a pressure gradient of venous flow. It has been pointed out that changes in peripheral resistance occurring near the right atrium greatly affect venous return, whereas changes in peripheral resistance occurring at progressively greater distances from the right atrium have progressively less effect on venous return. 随着右心房压力升高，影响心脏对心输出量增加的反应能力的因素已经简要讨论过。另一方面，影响静脉血液回流到心脏的不太流行的因素已经被更详细地讨论过，已经指出右心房压反对血液回流到心脏，而平均循环充盈压促进血液回流到心脏。平均循环充盈压和右心房压之间的差值代表静脉血流的压力梯度。已经指出，发生在右心房附近的外周阻力变化对静脉回流的影响很大，而发生在距离右心房越来越远的外周阻力变化对静脉回流的影响逐渐减小。
The various factors affecting venous return have been expressed in a formula. Also, it has been illustrated how venous return curves can be equated with cardiac response curves; by equating these curves both the cardiac output and the right atrial pressure are simultaneously determined. 影响静脉回流的各种因素已用公式表示。此外，还说明了静脉回流曲线如何等同于心脏反应曲线;通过使这些曲线相等，可以同时确定心输出量和右心房压。
REFERENCES 引用
i. Guyton, A. C., A. W. Lindsey and B. Kaufmann. Am. J. Physiol. In press. i. 盖顿，AC，AW Lindsey 和 B. Kaufmann。Am. J. Physiol. 出版中。
2. Guyton, A. C., J. H. Satterfield and J. W. Harris. Am. J. Physiol. 169: 691, 1952. 2. 盖顿，AC，JH Satterfield 和 JW Harris。美国生理学杂志 169：691,1952。
3. Guyton, A. C., D. Polizo and G. G. Armstrong. Am. J. Physiol. 179: 261, 1955. 3. 盖顿，AC，D. 波利佐和 G. G. 阿姆斯特朗。美国生理学杂志 179：261,1955 年。
4. Holt, J. P. Am. J. Physiol. 142: 594, 1944. 4. 霍尔特，JP Am. J. 生理学。142：594,1944 年。
5. Guyton, A. C. and L. H. Adkins. Am. J. Physiol. 177: 523, 1954. 5. 盖顿，AC 和 LH 阿德金斯。美国生理学杂志 177：523,1954 年。
6. Guyton, A. C. and A. W. Lindsey. Federation Proc. 13: 63, 1954. 6. 盖顿，AC 和 AW 林赛。联邦论文集 13：63,1954 年。
^(1){ }^{1} These investigations were supported in part by a research grant-in-aid from the National Heart Institute, National Institutes of Health, and in part by a grant-in-aid from the Mississippi Heart Association. ^(1){ }^{1} 这些检查部分得到了美国国立卫生研究院国家心脏研究所的研究资助，部分得到了密西西比州心脏协会的资助。
