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

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering

Background:

• Accurate assessment of left ventricular (LV) afterload is critical for understanding cardiac function.
• The aortic bulb (AB) plays a significant role in arterial hemodynamics, yet its specific contributions to LV afterload require detailed characterization.

Purpose of the Study:

• To quantify aortic bulb compliance (CAB) and longitudinal impedance properties (inertance, LVO; resistance, RVO) in the AB-aortic orifice region.
• To evaluate the impact of AB volume-accommodating actions on left ventricular outflow and pump properties.

Main Methods:

• Experiments were performed in open-chest dogs with simultaneous measurement of ascending aortic blood flow (Q) and pressures in the LV and ascending aorta.
• Sudden occlusion of the aorta distal to the flow probe isolated the AB for analysis during clamped beats.
• Analysis of pressure and flow data during preocclusion, occlusion, and occlusion-release phases.

Main Results:

• Mean CAB was 45 x 10(-4) cm5/dyn, LVO was 1.86 dyn·s2·cm-5, and RVO was 4.07 dyn·s·cm-5.
• The AB's volume accommodation significantly altered LV outflow compared to Q, resulting in nonisovolumic aortic-clamped beats.
• These findings highlight the AB's influence on arterial characteristic impedance and LV pump characteristics.

Conclusions:

• The aortic bulb's compliance and impedance are significant factors influencing left ventricular afterload.
• Understanding AB hemodynamics is essential for accurate estimation of LV pump properties, including time-varying elastance and internal resistance.