Influence of varying afterload upon left ventricular contractility.
In open-chest rabbits under pentobarbitone anaesthesia the left ventricular afterload was varied by occlusion of the carotid arteries, descending aorta and both of them together in alternating sequence when the aortic nerves and cardiac vagal nerves were cut. Ascending aortic flow AF was recorded by means of a flow probe around the aortic root, the left ventricular pressure LVP by direct canulating of the heart and the aortic blood pressure AP via catheter through the left subclavian artery. From the LVP the systolic and diastolic values LVSP and LVEDP, the contractility index CI = (dp/dt/p)max and from the AF the stroke volume SV and strokework W were evaluated. At mild afterload elevation (carotid or aortic occlusion alone) the CI appears to be enhanced, SV diminished, LVEDP only little raised, and W improved. At combined occlusions a drastical rise of LVEDP, decrease of SV and impairment of W is observed whereas the CI remains elevated and the LVSP increases with AP. From the pump function diagram ensues that at mild afterload increase the operational point is shifted towards the strokework optimum whereas at high afterload it is far away. After discharge of the ventricle all alterations are rapidly and completely restituted.
D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002346:Carotid Sinus / Q000502:physiology*; D009200:Myocardial Contraction; D011817:Rabbits; D013318:Stroke Volume