Hemodynamic and Pressure–Volume Responses to Continuous and Pulsatile Ventricular Assist in an Adult Mock Circulation

Abstract

This study investigated the hemodynamic and left ventricular (LV) pressure-volume loop responses to continuous versus pulsatile assist techniques at 50% and 100% bypass flow rates during simulated ventricular pathophysiologic states (normal, failing, recovery) with Starling response behavior in an adult mock circulation. The rationale for this approach was the desire to conduct a preliminary investigation in a well controlled environment that cannot be as easily produced in an animal model or clinical setting. Continuous and pulsatile flow ventricular assist devices (VADs) were connected to ventricular apical and aortic root return cannulae. The mock circulation was instrumented with a pressure-volume conductance catheter for simultaneous measurement of aortic root pressure and LV pressure and volume; a left atrial pressure catheter; a distal aortic pressure catheter; and aortic root, aortic distal, VAD output, and coronary flow probes. Filling pressures (mean left atrial and LV end diastolic) were reduced with each assist technique; continuous assist reduced filling pressures by 50% more than pulsatile. This reduction, however, was at the expense of a higher mean distal aortic pressure and lower diastolic to systolic coronary artery flow ratio. At full bypass flow (100%) for both assist devices, there was a pronounced effect on hemodynamic parameters, whereas the lesser bypass flow (50%) had only a slight influence. Hemodynamic responses to continuous and pulsatile assist during simulated heart failure differed from normal and recovery states. These findings suggest the potential for differences in endocardial perfusion between assist techniques that may warrant further investigation in an in vivo model, the need for controlling the amount of bypass flow, and the importance in considering the choice of in vivo model.

Numerical simulation of cardiovascular dynamics with different types of VAD assistance

“…Litwak et al (2004) examined the effect of constant flow and pulsatile flow VAD support and outflow graft location on aortic flow in an acute calf model. Litwak et al (2005) and Koenig et al (2004) conducted similar research in an adult mock circulation test rig. No differences in mean aortic flow between constant flow and pulsatile flow VADs were observed in their experimental results.…”

Alteration of LV end-diastolic volume by controlling the power of the continuous-flow LVAD, so it is synchronized with cardiac beat: development of a native heart load control system (NHLCS)

“…There are many reports comparing clinical outcomes and effects on circulatory dynamics after use of pulsatile and continuous-flow LVAD [1][2][3][4]. Continuous-flow LVAD with a pulsatile driving technique had not been tried or discussed before our group's report, however.…”

Erratum

“…

How Should Investigators Compare Different Perfusion Modes or Different Types of Pulsatile Flow During Chronic Support?

We read with great interest the article entitled "Hemodynamic and Pressure-Volume Responses to Continuous and Pulsatile Ventricular Assist in an Adult Mock Circulation" by Koenig and associates. 1 We have a few comments on this important investigation.The controversy over the benefits of pulsatile perfusion during chronic and acute support still continues because of the lack of understanding of the definition and quantification of arterial pressure and pump flow waveforms. Koenig and associates concluded that hemodynamic responses to continuous and pulsatile assist during simulated heart failure differed from normal and recovery states, and their findings suggest the potential for differences in endocardial perfusion between assist techniques.

…”

“…1 The authors investigated the hemodynamic and left ventricular pressure-volume loop responses to continuous versus pulsatile assist techniques at 50 and 100% bypass flow rates during simulated ventricular physiologic and pathophysiologic states in an adult mock circulation. 1 The authors investigated the hemodynamic and left ventricular pressure-volume loop responses to continuous versus pulsatile assist techniques at 50 and 100% bypass flow rates during simulated ventricular physiologic and pathophysiologic states in an adult mock circulation.…”