THE ENERGY INDEX
JOSEPH H. BARACH
Journal of the American Medical Association
on the heart in such a manner as to weaken the effi¬ ciency of the left side so as to lead to the accumulation of blood in the right side." H. C. Wood, Jr.,13 also by the blood-pressure method, noted a rise of pulmonary pressure after amyl nitrite, which he strongly suspected as being probably due to a pulmonary vasoconstriction. To quote his words, "It would seem almost proven by exclusion that the cause of the rise of pressure in the lesser circulation can be due only to contraction of the
... monary blood-vessels." Finally, a French observer, Petitjean,14 studying changes in pulmonary bloodpressure, and at the same time controlling his observa¬ tion "colorimetrically" by direct inspection of the exposed lungs, also noted a rise in pulmonary bloodpressure and a blanching of the lungs after the same drug. It will be seen that the observations of all these investigators would tend to speak for a vasoconstrictor action of the nitrites. After the effect of the nitrites on the arterial strip suspended in Locke's solution had been studied, the experiment was repeated, in order to approximate more to the condition in the living animal, by suspending arterial strips in blood-serum. Here too the same effect was observed. Finally the action of the nitrites was tested on strips of human pulmonary artery obtained from a fresh necropsy, and here too a vasoconstrictor effect was observed. It may be mentioned here that if preserved in fresh Locke's solution and kept in the ice-chest, I have seen such an artery respond to drugs twenty-five days after the post-mortem. In view of the foregoing observations, it will be seen that in causing a constriction of the pulmonary vessels and at the same time being efficient peripheral and splanchnic vasodilators, the nitrites meet the ideal requirements for therapeusis of pulmonary hemorrhage. Turning to clinical data, we find even there already some evidence of that being true. Francis Hare15 in 1906 reported nine cases of hemoptysis successfully checked by amyl nitrite. Rouget10 in 1905 reported ten similar cases. Graee-Calvert17 in 1907 speaks of having employed it successfully in pulmonary hemorrhage twenty times, and a few other cases are mentioned by Coiman,13 Smith19 and C4eorges Bouilard.20 It is to be hoped that my observations may contribute to more rational therapeusis of pulmonary conditions. The vasomotor action of the nitrites here described is not only interesting from the practical point of view, but also raises an equally interesting question as to the physiologic and pharmacologie explanation of that phe¬ nomenon. That is a subject, however, which I shall not discuss in this place, but which I hope to touch on in the fuller paper Thus far we have had no reliable method for estimating the functional capacity of the heart, although much has been written on the work done along this line, nor have we a certain and easily applicable method for determining the velocity of the blood. Aside from these, we need an index to the intravascular tension and to the amount of energy which the circulatory system expends in the course of a minute, an hour or a day. We need these particularly when we are dealing with cases in which the heart or the blood-vessels are endangered. The best means which we have at present for determining the expended energy of the circulatory system is the use of the mercury manometer. With this instrument, by the auscultatory method, we can accurately measure the arterial pressure at the time of systole and at the time of diastole of the heart. The systole gives us the energy factor in the work of the heart. The diastole gives us the energy factor in the peripheral resistance. From the pulse-rate we know how many systoles and how many diastoles to each minute there are in the arterial tree. For example, if the maximum pressure is 120 mm. Hg, the minimum pressure 70 mm. Hg and the pulserate 72 per minute, the exertion in one minute would be : In systole _ 120 mm. Hg X 72= 8,640 mm. Hg In diastole_ 70 mm. Hg X 72= 5.040 mm. Hg In both . 190 mm. Hg X 72 = 13,680 mm. Hg This, according to the most practical means we have, represents the total effort exerted per minute by the cardiovascular system. We may call it the energy index or S. D. R. index.1 The advantages of this method of indicating the expended energy of the cardiovascular system are that we are not deceived by the high maximum pressure when it is combined with a relatively low minimum pressure, or vice versa. It is a well-established clinical fact that the two pressures do not always tend in the same direction, and that one or the other may rise or fall. Also in this method, we do not neglect to consider the pulse-rate, which is an absolutely necessary element in properly estimating the expended energy of the cardio¬ vascular system in a given length of time. Judging by the clinical reports of the present day, the pulse-rate heretofore has largely been left out of this consideration. It is true that the number of pulsebeats per minute is not the greatest factor in producing high blood-pressure; but that each ventricular systole plays its part in the total blood-pressure is obvious, and that a greater number of systoles represents a greater total energy expenditure and a greater wear and tear is also clear enough. It is the last-mentioned factor par¬ ticularly which we may aim at estimating in our clin¬ ical work, and for v.! ich the S. D. R. index is most useful. 1. This method for obtaining an index to the cardiovascular energy is so simple that when its utility occurred to me I scarcely thought it possi[ill] that it had not been suggested long ago. In a search through [ill] literature at my command, I have not, however, been able to find it. Certain it is that it is not a recognized method, which I bel i eve it descrves to be.