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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



In summary, ventricular myocardial contraction 

 could have a threefold effect upon atrial filling: 

 /) It imparts so much energy to the arterial stream 

 that even after passing through the capillaries, the 

 blood continues to flow in the veins and fills the cen- 

 tral reservoirs; 2) during ventricular systole blood 

 is drawn actively into the atrium through an expan- 

 sion of the atrial cavities by a movement of the atrio- 

 ventricular junction toward the apex ("ventricular 

 systolic suction"); j) during ventricular diastole 

 the elastic forces, created by the preceding systole 

 in the ventricular walls, can aid in drawing blood 

 from the atrium into the ventricle and even in attract- 

 ing blood from the veins into the atrium ("ventric- 

 ular diastolic suction" upon the atrial content). 



VENTRICULAR FILLING 



While the forces causing ventricular ejection are 

 unquestionably those originating from myocardial 

 contraction, there is considerable debate concerning 

 the forces responsible for ventricular filling [for de- 

 tails see Brecher (19), Krug & Schlicher (95), El- 

 dridge & Hultgren (41), Bauereisen et al. (7)]. 

 The ejection of fluid from a pump is more spec- 

 tacular than the filling phase. This may be the reason 

 why the forces dealing with ventricular contraction 

 have received considerably more attention than the 

 forces dealing with ventricular filling. For a long 

 time it has been believed that the heart is filled ex- 

 clusively by a force which pushes blood into the ven- 

 tricle from behind [vis a tergo, Galli (50)]. This 

 force results from the preceding ventricular contrac- 

 tions and is imparted to the blood for circulating it 

 through the arteries, capillaries, and veins. Others 

 have maintained that some part of ventricular filling 

 is produced by a force from the front (vis a fronte) 

 which attracts or sucks blood from the atrium into 

 the ventricle. This force would manifest itself in 

 the ventricle during diastole and would probably be 

 caused by an elastic recoil of the ventricular walls. 

 It would lower the intraventricular pressure below 

 the level which would prevail if such a vis a fronte 

 did not exist. The history of the issue between vis a 

 tergo and vis a fronte is treated in detail by Ebstein 

 (40), Hamilton & Lombard (64), Bohme (14), 

 Brecher (19, 20), Krug & Schlicher (95). One can 

 summarize as follows the evidence in favor of the 

 existence of a vis a fronte: Ventricles of cold-blooded 

 animals, in the observations of Kraner & Ogden (94), 

 Kraner (93), Hennacy & Ogden (73), Hennacy (72), 



Peiper & Weigand (131), and of mammals according 

 to Bloom (13), Fowler et al. (48, 49) Brecher (19), and 

 O'Brien (123), can definitely suck in blood when the 

 filling pressure at the atrioventricular orifice is atmos- 

 pheric (zero) or subatmospheric (negative). Whether 

 or not ventricular suction also contributes to ventricu- 

 lar filling in the presence of a positive filling pressure 

 at the atrioventricular orifices has not yet been experi- 

 mentally established. 



It has been objected that the ventricles in which 

 suction forces were demonstrated had an abnormally 

 small functional residual capacity. The question there- 

 fore arises whether or not ventricles with physiological 

 volumes would also exert a suction force. Scheu & 

 Hamilton (143), using the intact spontaneously 

 breathing anesthetized dog, made simultaneous re- 

 cordings of the intraventricular and thoracic pres- 

 sure and thus established the transmural ventricular 

 pressure gradient. They held that "suction," prob- 

 ably by the elastic recoil of the ventricular walls, 

 could be demonstrated only if and when the trans- 

 mural pressure was negative. They concluded that 

 suction did not occur during normal diastole but 

 could be brought about by compressing the mitral 

 orifice or by hemorrhage. These two maneuvers 

 made the diastolic ventricular shadow smaller and 

 were thought to have reduced the residual blood to a 

 subnormal figure. 



Brecher & Kissen (23) demonstrated that dog 

 ventricles of an approximately normal functional 

 residual capacity filled by suction at zero ventricular 

 inflow pressure. Nevertheless, as long as there is not 

 unequivocal experimental proof of the existence of 

 ventricular diastolic vis a ironte in the unanesthe- 

 tized intact mammalian organism, one should be ex- 

 ceedingly cautious with any statement concerning 

 the role of diastolic suction in ventricular filling 

 [Brecher (20)]. 



Horres and his group (unpublished observations) 

 determined the average left ventricular volumes of 

 excised submerged hearts at equilibrium state and 

 found it to be 17 (±6) ml for dogs weighing 12 kg 

 (fig. 23). If one assumes that the elastic equilibrium 

 state of the relaxed ventricle in vivo is the same 

 as that of the freshly excised, and still responding 

 ventricle in vitro, then diastolic ventricular suction 

 could occur at any ventricular volume below the 

 equilibrium point (i.e., less than 17 ml). Unfor- 

 tunately the values of the functional residual capac- 

 ity reported for the dog heart vary too much to per- 

 mit an unbiased conclusion about the role of suction 

 in ventricular filling. According to the data of Holt 



