The invention relates to rotational pumps and methods for controlling rotational pumps.
Although research in the field of physiological control of rotary pumps dates back to the early 1990s rotary blood pumps (RBP) used as left ventricular assist devices (LVADs) were initially operated at a constant rotational speed which was adjusted individually according to the patient's need. Early clinical experience clearly showed that ventricular collapse and excessive suction are serious hazards related with the operation of these pumps.
These rotational blood pumps are implanted into a human body. The inlet of the blood pump is normally connectable to the left ventricle of the human, the outlet of a pump is connectable to the aorta, downstream of the aortic valve (AoV).
RBPs used as LVADs are often required to deliver the maximum possible flow rate. This may be the case in the early post-op period or when seriously impaired end-organ function requires optimum perfusion. Several approaches are known that attempt to meet this requirement by operating the pump near the collapse point of the LV, where the flow rate is as high as possible. On the other hand, it is known that excessive unloading of the LV may impair the pumping performance of the right ventricle because of the septum shift. Furthermore, it is hypothesized that the alteration of the natural flow path of the LV in combination with the greatly reduced LV wall movement due to full unloading causes recirculation and stasis inside the LV cavity. To date, there is only anecdotal evidence of thrombus formation in the LV, but atrial fibrillation can be considered to be a comparable situation in which thrombo-embolic complications are a well-known problem. Additionally, full unloading is contra-indicated for patients whose hearts may recover under assist and who are potential candidates for weaning. These facts strongly indicate that it may be better not always to operate the RBP at the point of maximum flow rate but also at a point where unloading is only partial, LV volume and LV wall movement are not minimal and at the optimum achievable washout of the LV cavity and where the aortic valve opens at least occasionally.
It is the object of the invention to provide a rotational blood pump and a control method which finds and adjusts the optimum operating point under all conceivable physiological situations without requiring the attention of a physician. An operating point may be optimal with regard to the therapeutic objectives mentioned above and which can be classified into two cases: Full Assist (FA)—maximum support with closed AoV but sufficient safety margin to avoid suction, and Partial Assist (PA)—moderate support at the transition region between the opening of the AoV and a permanently-closed AoV with near-physiological LV volume, better LV washout and moderate LV loading.