CIRCULATION. 677 



It is very probably occasioned in part by the tions which give rise to a great and immediate 



assistance which the ventricular systole receives increase of the frequency of the heart's action, 



from the collapse of the parietes of the chest at the respiration becomes hurried and forcible, or 



the time that the air is expelled from that ca- there is panting ; but, on the other hand, it 



vity, and in part by pressure of the parietes of does not appear that the gradual changes of the 



the chest upon its contents, and through them pulse, which are liable to occur from one pe- 



upon the trunks of the larger arteries. During riod of the day to another, are accompanied by 



inspiration the pressure must be, to a certain corresponding variations in the frequency of 



amount, removed from the larger arteries, and respiration ; and again, when by a voluntary 



consequently the current of blood through them effort we breathe very hurriedly, as for example, 



at that period will be less forcible and less from 80 to 100 times in a minute, the fre- 



rapid. quency of the pulse is not increased by more 



The well-known fact that rupture of aneu- than 8 or 10 beats in a minute.* 



risms of the large arteries and effusion of blood Some physiologists hold the opinion that the 



within the cranium in apoplexy are more liable motion of the blood in the capillaries of the 



to occur during straining and other muscular lungs and the system is considerably influenced 



efforts associated with forcible expiration, is a by the chemical changes which the blood un- 



further illustration of the fact that the arterial dergoes in its passage through the minute pul- 



pressure is greatest at the time of the collapse monary and systemic vessels. We are not ac- 



of the parietes of the chest. quainted with any facts or experiments which 



The relation of the force and frequency of shew that the systemic capillary circulation is 

 the pulse to the activity of the respiration is an immediately dependent upon the change of the 

 interesting subject connected with the facts at arterial into venous blood : on the contrary, 

 present under consideration.* In many per- such an opinion is much opposed by the facts 

 sons, in ordinary and tranquil respiration, the that a free circulation of imperfectly arterialized 

 force and frequency of the pulse vary percepti- blood takes place in the foetus before birth, as 

 bly during inspiration and expiration, and in well as in many children after birth affected with 

 these persons, when the respiration is more malformations of the heart or greater vessels, 

 forcible than natural, the pulse indicates very and that a completely venous blood circulates 

 distinctly by its changes the varying states of through the system in hybernating animals 

 the chest. During an unusually long and for- when in the state of deepest torpidity. There 

 cible inspiration the beats of the pulse are more are, however, several circumstances which appear 

 rapid and weaker, and during a succeeding to justify the opinion that the motion of blood 

 complete expiration, or even while the chest through the pulmonary capillaries has a more 

 is kept expanded, the pulse is more full, immediate dependence on the change of arte- 

 strong, and slow. Some individuals have the rialization.f In all those circumstances which 

 power of occasioning an intermittent pulse, and cause imperfect respiration and prevent the ac- 

 some of causing the action of the heart to cease customed necessary arterialization of the blood, 

 even by forcible exertion of the expiratory mus- or in approaching asphyxia, it seems to follow 

 cles. We think it probable that it may have from the experiments of Dr. Kay, Alison, and 

 been in this or some similar indirect manner Reid, that there occurs from the very first corn- 

 that the action of the heart was arrested in mencement of the symptoms of impeded respi- 

 Colonel Townsend's case, described by Dr. ration, a diminution of the quantity of blood 

 Cheyne in his work on the English malady, which passes through the pulmonary capillaries, 

 and very often referred to as a proof of the pos- There is thus produced from the first corn- 

 session by Colonel Townsend of a voluntary mencement of non-arterial zation of the blood 

 power of influencing directly the heart's action, an accumulation of venous blood in the pulmo- 



There is in general a very constant proper- nary capillaries and arteries, but it is equally 

 tion in the ordinary state of the circulation be- well proved that a certain quantity of venous 

 tween the number of the beats of the pulse and blood does, as Bichat shewed, gain the left 

 the frequency of respiration. The average side of the heart and permeate the arterial sys- 

 number of respirations in a healthy person may tern. As the symptoms, however, of suffocation 

 be considered as from 15 to 20 in a minute, or asphyxia become more urgent, the accumu- 

 and taking the number of the pulse in the same lation of blood in the pulmonary artery on the 

 time at from 72 to 75, this makes one complete right side of the heart and in the systemic veins 

 respiratory motion for nearly four beats of the gradually increases, until by the time that the 

 heart. The force and frequency of the heart's involuntary motions of respiration have ceased, 

 action and consequent state of the pulse are there appears to be a complete stagnation in the 

 well known to be considerably influenced by lungs, although the heart continues to beat a 

 very slight muscular efforts, as well as by little longer. During the occurrence of these 

 changes of position of the body even ; but it is changes the action of the heart also is no doubt 

 not observed that the respiration becomes inva- gradually becoming weaker, a circumstance 

 riably more or less hurried in a corresponding which may very probably contribute to the stag- 

 degree with an increased or diminished fre- nation of the blood in the lungs, but there is good 

 quency of the pulse. In very violent exercise, 



it is true, and more particularly in rapid mo- 

 See an account of the interesting experiments 



by M. Roulin on the variations of the pulse at diffe- 



* See an interesting Essay by Hering in Tiede- rent heights. Magendie's Journ. Jan. 1826. 



mann's Zeitschrift, vol. v. " t See Dr. Alison's Remarks, loe. cit. 



