Aortic bulb-aortic orifice hemodynamics in left ventricle-systemic arterial interaction

Experiments were conducted in open-chest dogs in which ascending aortic blood flow (Q) was measured with an electromagnetic flow probe, and pressure was measured in the left ventricle (LV) and ascending aorta. The aorta just distal to the flow probe was occluded suddenly, causing the aortic bulb (AB) to be the only part of the arterial system to be in communication with the LV during clamped beats. Pressure and flow data from preocclusion, occlusion, and occlusion-release periods were analyzed to assess AB compliance (CAB) and the longitudinal impedance properties of inertance (LVO) and resistance (RVO) in the AB-aortic orifice region. In five dogs (avg wt 24.2 kg), the mean and range of values were as follows: CAB = 45 (31-55) X 10(-4) cm5/dyn; LVO = 1.86 (0.76-2.88) dyn X s2 X cm-5, RVO = 4.07 (0.66-8.55) dyn X s X cm-5. The volume-accommodating actions of CAB caused actual LV outflow to be characteristically different from Q and aortic-clamped beats to be nonisovolumic. Actions of the AB were found to be important in the estimation of arterial characteristic impedance as a component of LV afterload and in the estimation of the LV pump properties of time-varying elastance and internal resistance.