CIRCULATION. 



677 



It is very probably occasioned in part by the 

 assistance which the ventricular systole receives 

 from the collapse of the parietes of the chest at 

 the time that the air is expelled from that ca- 

 vity, and in part by pressure of the parietes of 

 the chest upon its contents, and through them 

 upon the trunks of the larger arteries. During 

 inspiration the pressure must be, to a certain 

 amount, removed from the larger arteries, and 

 consequently the current of blood through them 

 at that period will be less forcible and less 

 rapid. 



The well-known fact that rupture of aneu- 

 risms of the large arteries and effusion of blood 

 within the cranium in apoplexy are more liable 

 to occur during straining and other muscular 

 efforts associated with forcible expiration, is a 

 further illustration of the fact that the arterial 

 pressure is greatest at the time of the collapse 

 of the parietes of the chest. 



The relation of the force and frequency of 

 the pulse to the activity of the respiration is an 

 interesting subject connected with the facts at 

 present under consideration.* In many per- 

 sons, in ordinary and tranquil respiration, the 

 force and frequency of the pulse vary percepti- 

 bly during inspiration and expiration, and in 

 these persons, when the respiration is more 

 forcible than natural, the pulse indicates very 

 distinctly by its changes the varying states of 

 the chest. During an unusually long and for- 

 cible inspiration the beats of the pulse are more 

 rapid and weaker, and during a succeeding 

 complete expiration, or even while the chest 

 is kept expanded, the pulse is more full, 

 strong, and slow. Some individuals have the 

 power of occasioning an intermittent pulse, and 

 some of causing the action of the heart to cease 

 even by forcible exertion of the expiratory mus- 

 cles. We think it probable that it may have 

 been in this or some similar indirect manner 

 that the action of the heart was arrested in 

 Colonel Townsend's case, described by Dr. 

 Cheyne in his work on the English malady, 

 and very often referred to as a proof of the pos- 

 session by Colonel Townsend of a voluntary 

 power of influencing directly the heart's action. 



There is in general a very constant propor- 

 tion in the ordinary state of the circulation be- 

 tween the number of the beats of the pulse and 

 the frequency of respiration. The average 

 number of respirations in a healthy person may 

 be considered as from 15 to 20 in a minute, 

 and taking the number of the pulse in the same 

 time at from 72 to 75, this makes one complete 

 respiratory motion for nearly four beats of the 

 heart. The force and frequency of the heart's 

 action and consequent state of the pulse are 

 well known to be considerably influenced by 

 very slight muscular efforts, as well as by 

 changes of position of the body even ; but it is 

 not observed that the respiration becomes inva- 

 riably more or less hurried in a corresponding 

 degree with an increased or diminished fre- 

 quency of the pulse. In very violent exercise, 

 it is true, and more particularly in rapid mo- 



* See an interesting Essay by Hering in Tiede- 

 maun's Zeitschrift, vol. v. 



tions which give rise to a great and immediate 

 increase of the frequency of the heart's action, 

 the respiration becomes hurried and forcible, or 

 there is panting ; but, on the other hand, it 

 does not appear that the gradual changes of the 

 pulse, which are liable to occur from one pe- 

 riod of the day to another, are accompanied by 

 corresponding variations in the frequency of 

 respiration; and again, when by a voluntary 

 effort we breathe very hurriedly, as for example, 

 from 80 to 100 times in a minute, the fre- 

 quency of the pulse is not increased by more 

 than 8 or 10 beats in a minute.* 



Some physiologists hold the opinion that the 

 motion of the blood in the capillaries of the 

 lungs and the system is considerably influenced 

 by the chemical changes which the blood un- 

 dergoes in its passage through the minute pul- 

 monary and systemic vessels. We are not ac- 

 quainted with any facts or experiments which 

 shew that the systemic capillary circulation is 

 immediately dependent upon the change of the 

 arterial into venous blood : on the contrary, 

 such an opinion is much opposed by the facts 

 that a free circulation of imperfectly arterialized 

 blood takes place in the foetus before birth, as 

 well as in many children after birth affected with 

 malformations of the heart or greater vessels, 

 and that a completely venous blood circulates 

 through the system in hybernating animals 

 when in the state of deepest torpidity. There 

 are, however, several circumstances which appear 

 to justify the opinion that the motion of blood 

 through the pulmonary capillaries has a more 

 immediate dependence on the change of arte- 

 rialization.f In all those circumstances which 

 cause imperfect respiration and prevent the ac- 

 customed necessary arterialization of the blood, 

 or in approaching asphyxia, it seems to follow 

 from the experiments of Dr. Kay, Alison, and 

 Reid, that there occurs from the very first com- 

 mencement of the symptoms of impeded respi- 

 ration, a diminution of the quantity of blood 

 which passes through the pulmonary capillaries. 

 There is thus produced from the first com- 

 mencement of non-arterializution of the blood 

 an accumulation of venous blood in the pulmo- 

 nary capillaries and arteries, but it is equally 

 well proved that a certain quantity of venous 

 blood does, as Bichat shewed, gain the left 

 side of the heart and permeate the arterial sys- 

 tem. As the symptoms, however, of suffocation 

 or asphyxia become more urgent, the accumu- 

 lation of blood in the pulmonary artery on the 

 right side of the heart and in the systemic veins 

 gradually increases, until by the time that the 

 involuntary motions of respiration have ceased, 

 there appears to be a complete stagnation in the 

 lungs, although the heart continues to beat a 

 little longer. During the occurrence of these 

 changes the action of the heart also is no doubt 

 gradually becoming weaker, a circumstance 

 which may very probably contribute to the stag- 

 nation of the blood in the lungs, but there is good 



* See an account of the interesting experiments 

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

 rent heights. Magendie's Journ. Jan. 1826. 



t See Dr. Alison's Remarks, loc. cit. 



