CHAPTER VIII 

 DRUGS ACTING UPON THE CIRCULATORY SYSTEM 



These may be roughly divided into (1) circulatory stimulants, 

 (2) circulatory depressants, (3) vasodilators and (4) vasoconstric- 

 tors. The circulatory system consists in the main of the heart or 

 pumping organ and the blood vessels. The action of the heart con- 

 sists of a rhythmical contraction (systole) and dilatation (diastole). 

 The blood is under positive pressure during systole and under nega- 

 tive pressure during diastole, corresponding respectively to the forc- 

 ing and sucking action of a pump. The pause or period of rest is 

 very important because it gives opportunity for rest and recuperation 

 of the organ, vchile the valves serve to regulate the flow of blood. 

 The nerves of the heart are the vagus or inhibitory and the sympa- 

 thetic or accelerator. There are also some automatic intracardiac 

 centers. The heart muscle and nerves may be stimulated by mechan- 

 ical, chemical, thermal and electrical means, while the heart may be 

 paralyzed or depressed by drugs, disease of the myocardium, over- 

 exertion, deficiency of oxygen, lack of nourishment and collection of 

 carbon dioxide and other products of decomposition in the blood. 



1. CIRCULATORY STIMULANTS 



These are agents which increase the efiBciency of the heart. 

 They may increase the force of the beat and lessen the rate, or may 

 increase both the force and rate. The best examples of those increas- 

 ing the force but decreasing the rate belong to the digitalis group 

 and are : 



Digitalis Squill 



Strophanthus Apocynum (Canadian Hemp) 



Convallaria Adrenaline 



Adonis Vernalis Strychnine 



Those increasing both rate and force are : 



Caffeine Atropine 



There are several drugs which reflexly stimulate the heart and 

 increase the number of beats, increasing the output of the heart per 

 unit of time. Their effect, however, is but transitory. 



Most prominent of this class are : 



Ammonia Ether 



Alcohol Camphor 



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