1564 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



trials is very difficult due to the variability of the 

 disease and its response to many extraneous factors. 

 Nitroglycerin remains the only universally preferred 

 treatment. Other agents, including the long-acting 

 nitrates, have received some favorable but also many 

 unfavorable reports. The mode of action of the mono- 

 amine oxidases is unknown although the clinically 

 beneficial but toxic iproniazid has been demonstrated 

 to increase coronary flow and depress cardiac con- 

 traction in isolated hearts (160). Anticholesterol 

 agents and thyroid are used in the hope of decreasing 

 the atherosclerotic process, but long-term studies are 

 needed to assess their value. However, study of 

 hyperthyroid patients shows that their myocardial 

 oxygen utilization is increased more than would be 

 expected from the increased heart rate (3 17)- 



Table 1 is a compilation of data concerning the 

 action of the vasopressor agents most commonly used 

 in cardiogenic shock. Since most of these studies were 

 performed in normal animals or man, the question 

 again arises whether the information can be applied 

 to the diseased state. Against such application is the 

 demonstration that drugs may act differently in a 

 normal, as compared to a failing heart, i.e., mephen- 

 termine may exert a myocardial oxygen-conserving 



effect in failing animal hearts but an oxygen-wasting 

 action in normal hearts (391). Since the etiology of 

 cardiogenic shock is undetermined (decreased pe- 

 ripheral resistance, or myocardial failure or both), 

 controversy exists regarding its treatment. The 

 question concerns whether an agent should be used 

 which not only increases coronary flow and blood 

 pressure (methoxamine), but also stimulates the 

 myocardium and, therefore, increases myocardial 

 oxygen consumption (epinephrine, levarterenol, 

 metaraminol, and mephentermine) (13, 237). It 

 appears that clinical results favor the latter concept, 

 for levarterenol has met with the most success. Also, 

 in animal studies the vasopressor agents which stimu- 

 late myocardial contractility and lower atrial pressure 

 are more beneficial to the "failing" heart (332). 

 However, methoxamine has been shown to be of 

 use for increasing the blood pressure and coronary 

 flow in hemorrhagic shock in animals, and also in 

 cardiogenic shock in patients (13). A useful agent for 

 cardiogenic shock should increase coronary flow, 

 stimulate myocardial contractility, and raise the 

 blood pressure and cardiac output, but should not 

 increase myocardial oxygen consumption in relation 

 to its workload. It was pointed out above that myo- 



table 1. Pressor Agents Used in Cardiogenic Shock* 



* Results in man. Figures in parentheses indicate if dogs react differently or if only dog results are available. 

 Key: I. V. = intravenous; I. C. = intracoronary ; + = increase; o = no change; — = decrease; ± = variable effects or 

 conflicting data; t = venous pressure. 



