Overview
Mechanical support separates native ventricular ejection from device flow. Systemic perfusion can improve while the native arterial pulse and ventricular loop become smaller. A flat arterial line under continuous support does not necessarily mean zero systemic flow.
Device settings are flow targets in a bounded teaching model. Filling, pressure head, RV delivery, valve disease and competing drainage determine effective flow. They are not clinical pump curves, P-levels or guaranteed device outputs.
Device flow targets
All values are L/min before the model applies filling and loading limits.
| Device | Off | Low | Medium | High |
|---|
| V-A ECMO | 0 | 2 | 3.5 | 5 |
|---|
| Impella 2.5 | 0 | 1 | 1.8 | 2.5 |
|---|
| Impella CP | 0 | 1.5 | 2.5 | 3.5 |
|---|
| Impella 5.0 | 0 | 2 | 3.5 | 5 |
|---|
Flow paths and ventricular loading
V-A ECMO drains venous blood and returns it to the arterial circulation. Total systemic flow includes circuit return; pulmonary flow excludes that bypass. Retrograde arterial support can increase LV afterload, LVEDP and wedge if the LV cannot eject adequately.
Impella drains the LV into the aorta continuously. RV delivery and LV filling limit pump inflow. Combining ECMO and Impella can offset LV loading, but venous drainage can also reduce available LV inflow. Neither device inherently converts VF or restores organized contraction.
Pressure reservoirs and pulse shape
Systemic pressure combines continuous inflow with native ejection into a resistance/compliance reservoir. Pulmonary pressure uses a separate pulmonary reservoir and the pulmonary flow path. Mean PA = wedge + PVR × pulmonary flow remains the governing mean relationship.
Continuous flow sustains diastolic pressure. With no native ejection, the arterial trace is flat at a supported mean rather than a scaled normal pulse. Fine closure-notch, reflection and pump pressure-head fluctuations are not resolved. LV/RV pressure functions and PV accounting distinguish native ejection from pump drainage.
SVR after restored perfusion
When support improves a low-output pump-failure state, a bounded later-equilibrium feedback relaxes part of the compensatory vasoconstriction. Selected pressor/vasodilator effects remain. An explicitly set manual SVR overrides this feedback. This prevents restored flow from being multiplied by an indefinitely fixed shock-related resistance.
The feedback is not an instantaneous clinical autoregulation guarantee. Low filling, obstruction and important regurgitation can still cause ineffective support or worsening congestion. The warning logic evaluates those risks separately.
IABP is counterpulsation
IABP augments diastolic aortic pressure and reduces subsequent ejection load in the selected response. Ratios 1:1, 1:2 and 1:3 distinguish assisted beats. Early inflation interferes with ejection; late inflation loses part of diastolic augmentation. A balloon pressure trace is not a direct LV pressure hump.
AR and dynamic obstruction have explicit adverse-use behavior. IABP does not replace missing circulating volume, drain tamponade or generate a full ECMO-like continuous circulation. Device complications, cannulation, hemolysis, thrombosis and detailed oxygenator mixing are outside the model.
References & further reading
