304 



THE MECHANICS OF THE HEART 



this organ and the metal capsule, was filled with oil and was connected 

 with a piston-recorder by means of tubing. Under very favorable 

 conditions the excursions of this instrument should correspond 

 precisely to the variations in the volume of the beating heart. This 

 result, however, is not obtained under ordinary circumstances, because 

 even this type of cardiometer does not meet all the requirements of 

 a perfect instrument of precision. Johannson and Tigerstedt have 

 overcome these difficulties in a measure by employing a bulbular cap- 

 sule just large enough to envelop the ventricular 

 portion of the heart. The round opening at its 

 upper pole is closed by a rubber membrane with 

 a central perforation through which the ven- 

 tricle is inserted. Henderson 1 has made use of 

 hemispherical capsules of glass, and of ordinary 

 rubber balls cut in half. Great care must be ex- 

 ercised that the opening in the rubber mem- 

 brane is not too small, otherwise the filling of 

 the ventricles will be seriously impaired. Roth- 

 berger, 2 who has measured the ventricular dis- 

 charge directly, finds that exact values cannot 

 be obtained with cardiometers even under the 

 most favorable conditions. 



The attempt has been made by Burton- 

 Opitz 3 to calibrate the systolic discharge of the 

 right ventricle with the help of a recording 

 stromuhr, or current measurer. Piston and 

 syphon recorders have been employed by 

 Stolnikow 4 and Starling. 5 The systolic-diastolic 

 changes in the beating heart can also be made 

 out very clearly during transillumination of the 

 ihest by means of the Rontgen rays. 



It may be said in a general way that a rapid heart discharges more 

 blood in a given period of time than a slow one. This statement, 

 however, does not hold true under all conditions, because it can readily 

 be demonstrated that the ventricular output may vary even when the 

 cardiac frequency remains the same, while, at another time, the output 

 may remain practically unchanged in spite of the fact that the fre- 

 quency of the heart is either increased or decreased. This result 

 indicates that the cardiac output per unit of time is dependent not only 

 upon the number of systoles, but also upon the quantity of blood ejected 

 each time. As the latter factor represents the filling power or capa- 

 ciousness of the heart, it must be evident that the relaxability of the 



1 Am. Jour, of Physiol., xvi, 1906, 325. 



2 Pfluger's Archiv, 118, 1907, 353. 



3 Proc. Soc. for Exp. Biology and Medicine, 1903. 



4 Archiv fur Anat. und Physiol., 1886, i. 



5 Jour, of Physiol., xlv, 1912, 164. 



FIG. 156. CARDIO- 

 METER. 



The heart is inserted 

 through a perforation in 

 rubber membrane (R) 

 into cavity of a hemis- 

 pherical glass capsule 

 (C) . The latter is con- 

 nected with a recording 

 tambour (T). 



