This equilibrium point is relatively viable For example, let at a given moment

mm Hg. This equilibrium point is relatively viable For example, let at a given moment. I, the CVP is suddenly raised The first heart beat after the , because of the Frank-Starting mechanism, will have a greater stroke volume But because of this greater stroke volume, translocation of blood from the venous side to the arterial side will be greater and so the CVP will be somewhat lesser in the following beat Therefore, immediately after .the equilibrium point will shift no doubt, but it will try. to return to the original point gradually. Fig. 5.5.5. To show that when cardiac output rises, the rap' falls Fig. 5.5.6. See text FACTORS INFLUENCING VENOUS RETURNS 1. When the cardiac output rises, the velocity of circulation raised which results in greater cardiac inflow (= venous return to the. heart) per unit time Explanation (I) as the cardiac output rises, as explained above, the central venous pressure falls hence pressure in the peripheral veins also falls. (II) as the cardiac output rises, a little extra blood is pushed into the arterial system per beat As the arterial system resists distension even a slight increases in blood volume in it (the arterial system). causes a sharp rise of arterial BP When the above two factors, vast (I) and (ii) are considered together, it becomes obvious that the pressure gradients between the arterial and venous system (= the difference between arterial BP and venous BP) rises. This increase in the pressure radiance results in greater rate of flow of blood from the arterial to the venous side, stated simply this means greater venous return per unit time. 2. The respiratory pump During inspiration, the intrapleural pressure as well as (he intrathoracic pressure as a whole becomes more negative The intra abdominal pressure however rises due to the descent of the diaphragm Because of the increasing negativity, the diameters of the vane cave increase, and the BP within them falls So the pressure radiance (the difference of BP s between the intra abdominal part of the inferior vane cava and The right atrium) increases — flow of blood towards the right atrium increases. Conclusion,