1044 



PHYSIOLOGY 



Frank has pointed out, in the first place, that all the instruments hitherto used, 

 including the manometers of Hurthle, are not nearly delicate enough to register 

 the very rapid changes of pressure which occur in the heart at the beginning of 

 the arterial system. The best instruments hitherto used, as applied to the body 

 i.e. with their connecting tubes, cannula, &c. possess an instrumental vibra- 

 tion frequency of not more than 10 to 15 per second. If we consider that the 

 systole of a rabbit's heart beating over 200 times per minute may last less than a 

 tenth of a second, we see that the curve of endocardiac pressure obtained by such 

 instruments would be seriously deformed by the vibrations set up in the instru- 

 ment itself. The manometer of Frank described above has a vibration frequency 

 of 180 per second. This efficiency is attained by getting rid of the recording lever, 



FIG. 418. Four different types of pulse curve, from the radial artery. 



(MACKENZIE.) 



These were taken from a patient during recovery from an attack of acute 

 dilatation of the heart. Note the gradual rise in the height of the systolic 

 notch. No. 4 was taken after complete recovery. 



using a beam of light for this purpose, by having a short wide tube connecting 

 the manometer with the interior of the artery, by avoiding all rubber connections, 

 and by scrupulous exclusion of air bubbles in the apparatus. 



A similar apparatus has been employed by Straub. The results obtained by 

 these methods may be shortly summarised as follows : 



(a) The curve of endocardiac pressure in the ventricle is quite simple and 

 similar to the contraction curve of a voluntary striated muscle (Straub). There 

 is no systolic plateau, nor are there any superposed vibrations. The systolic 

 vibrations are, according to Frank, entirely instrumental in origin. 



(b) The aortic pressure curve (Fig. 419) is also rounded at the top. It presents 

 one set of vibrations during the systole at the point where the very rapid rise of 

 pressure begins to slow off. A second depression followed by an elevation signalises 

 the beginning of relaxation of the ventricle, with a slight back-flow of blood on 

 to the aortic valves and the rebound from these valves as they are closed by 

 the regurgitant wave. At the end of the diastolic descent of the curve are 

 some small vibrations which mark the beginning of the ventricular contrac- 

 tion. The sudden rise of pressure in the ventricles, even before the aortic valves 



