188 



PULSE. 



it is necessary to premise that the increase or 

 diminution of frequency attending the change 

 from one posture to another, is not merely a 

 transient effect, dependent upon the muscular 

 effort involved in the act of change, but a 

 permanent state, continuing as long as the 

 respective postures are maintained. This was 

 long since stated by Dr. Graves *, who proved 

 experimentally that when the posture of the 

 body was changed without any effort of its 

 own muscles, " the difference between the 

 frequency in the horizontal and erect postures 

 was not less than when muscular exertion 

 was used." The mode in which Dr. Graves 

 effected this change of posture is not stated ; 

 but in experiments performed by the writer 

 of the present article, by means of a revolving 

 board -f , a difference amounting to less than 

 a single beat was found to exist between the 

 average of twenty experiments, in which the 

 body "was transferred from one posture to 

 the other by the machine, and an average of 

 twenty experiments, in which the change of 

 posture was effected by the voluntary efforts 

 of the same persons. The round numbers 

 with the machine were, standing 87, lying 

 74, difference 13; without the machine, 

 standing 89, lying 77, difference 12. This 

 very, slight difference is due to the effort of 

 the muscles in effecting the change of posi- 

 tion. When this is subtracted there still 

 remains a much more considerable difference 

 attributable to some permanent cause, which 

 may be either the continuance of muscular 

 effort, or some other condition. The differ- 

 ence of opinion which has existed upon this 

 subject, gives an interest to the following brief 

 summary of the explanations advanced by the 

 leading writers on the pulse. 



Bryan Robinson J, Falconer , and Knox, 

 without attempting to submit the question to 

 the t^st of experiment, attribute, directly of by 

 inference, the different frequency of the pulse, 

 in different postures, to muscular contraction. 

 Dr. Graves || , however, confesses himself to l?e 

 altogether at a loss for an explanation ; Dr 

 Arnott U seems to refer it to the more or less 

 favourable position of the body, in respect to 

 gravity, while other authors attribute it to the 

 varying positions of the heart and its valves.** 

 Very little consideration is required to show 

 the futility of all the other causes, except that 

 assumed by Robinson, Falconer, and Knox. 

 The two postures between which there is the 

 most marked difference in the frequency of 

 the pulse, viz. the erect and sitting postures, 

 are precisely those in which there is no dif- 

 ference in the position of the heart or its 

 valves, and very little difference in the re- 

 sistance offered to the circulation ; while the 



* Op. cit. p. 562. 



t Guy's Hospital Reports, No. VI. 

 ' Op. cit. p. 177. 

 Op. cit. p. 34. 

 Op. cit. p. 570. 



Elements of Physics, vol. i. p. 570. 

 ""* See an Essay by Mr. Blackley, " On the Cause 

 of the Pulse being affected by the Position of the 

 Body," in the Dublin Journal of Medical and Che- 

 mical Science, July, 1834. 



sitting and recumbent postures, between 

 which there is so slight a difference in the 

 number of the pulse, are accompanied by a 

 marked change in the position of the heart 

 and its valves, and of the column of blood to 

 be propelled. On the other hand, the dif- 

 ference in the amount of muscular contraction 

 required to support the body in the erect and 

 sitting postures, is much more considerable 

 than that required to support the body in the 

 sitting and recumbent positions differences 

 in strict conformity with the observed fre- 

 quencies of the pulse in the several postures. 

 This simple process of reasoning, therefore, 

 serves to show the fallacy of the explanations 

 now alluded to, and the reasonableness of 

 the remaining alternative muscular contrac- 

 tion. 



With this strong probability the authorities 

 just cited seem to have been satisfied ; and as 

 it did not occur to them to submit this very 

 reasonable theory to the test of actual ex- 

 periment, it was reserved for the writer of this 

 article to place this mooted question beyond 

 the reach of doubt. 



The experiments required for this purpose 

 were of the very simplest kind. It was merely 

 necessary in successive experiments to place 

 the body in such circumstances as to exclude 

 every other assigned cause but the contraction 

 of the muscles ; in other words, the position 

 of the body, and consequently of the organs 

 of the circulation, remaining the same, first to 

 support the body, and then to call its own 

 muscles into action to maintain its position. 



The following are the results of a series of 

 such experiments. 



1. Difference between the pulse in the erect 

 posture, without support, and leaning in the 

 same posture, on an average of twelve experi- 

 ments on the writer, 12 beats; and on an 

 average of eight experiments on other healthy 

 males, 8 beats. 



* 2. Difference in the frequency of the pulse 

 in the recumbent posture, fully supported, and 

 partially supported, 14? beats, on an average of 

 five experiments. 



3. Sitting posture (mean of ten experiments 

 on the writer), back supported, 80; unsup- 

 ported, 87; difference, 7 beats. 



4. Sitting posture with the legs raised at 

 right angles to the body (average of twenty 

 experiments on the writer), back unsup- 

 ported, 86; supported, 68 ; difference, 18 beats. 

 An average of fifteen experiments of the 

 same kind on other healthy males gave the 

 following numbers : back unsupported, 80; 

 supported, 68; being a difference of 12 beats. 



These experiments, with the simple reason- 

 ings already advanced, serve to demonstrate 

 the true cause of the varying frequency of the 

 pulse in different postures of the body to be 

 muscular contraction. 



The effect of an inverted position of the 

 body on the frequency of the pulse has been 

 made the subject of experiment by Dr. Graves, 

 and subsequently by the writer of this essay. 

 The reader is referred for an exact account 

 of the experiments to the Guy's Hospital 



