Rotary blood pump and control system therefor

Abstract

A pump assembly and estimation and control system therefor, the pump adapted for continuous flow pumping of blood. In a particular form, the pump is a centrifugal pump wherein the impeller is entirely sealed within the pump housing and is exclusively hydrodynamically suspended therein against movement in three translational and two rotational degrees of freedom as the impeller rotates within the fluid urged by electromagnetic means external to the pump cavity. Hydrodynamic suspension is assisted by the impeller having deformities therein such as blades with surfaces tapered from the leading edges to the trailing edges of bottom and top surfaces thereof.

1 . A method of hydrodynamically suspending and controlling an impeller within a rotary pump for support in at least one of a radial and axial direction; the method comprising: 
 incorporating a deformed surface in at least part of the impeller so that, in use, a thrust is created between the deformed surface and an adjacent pump housing during relative movement therebetween; and    maintaining the speed of rotation of the impeller within a range whereby the impeller, in use, substantially resists five degrees of freedom of movement with respect to the pump housing without any external intervention.    
     
     
         2 . The method of  claim 1  wherein the deformed surface includes a taper.  
     
     
         3 . The method of  claim 2  wherein the taper is arranged so that there is a larger gap at a leading edge thereof between the impeller and the pump housing than at a trailing edge thereof.  
     
     
         4 . An estimation and control system for a pump; the pump of the type having an impeller located within a pump cavity in a pump housing; the housing having a fluid inlet in fluid communication with the cavity; the housing having a fluid outlet in fluid communication with the pump cavity; the impeller urged to rotate about an impeller axis so as to cause fluid to be urged from the inlet through the pump cavity to the pump outlet; the impeller urged to rotate by an impeller drive; the impeller supported for rotational movement by an impeller support; the pump maintained at or near a predetermined operating point by a controller acting on the impeller drive; the controller receiving as input variables at least a first input variable derived from the impeller drive; the controller receiving at least a second input variable also derived from the impeller drive; the controller thereby calculating an estimate of the operating point to an approximation of predetermined accuracy relying on signals available from the impeller drive; the controller controlling the pump by comparing the predetermined operating point with the estimate of the operating point; and wherein the pump is arranged to operate according to a relatively flat pressure versus flow rate characteristic.  
     
     
         5 . The estimation and control system of  claim 4  wherein there is no inflexion point in the pressure versus flow rate characteristic at or near the predetermined operating point.  
     
     
         6 . The estimation and control system of  claim 4  wherein the pump includes near-radial off-flow from the impeller.  
     
     
         7 . The estimation and control system of  claim 4  wherein the pump has a low specific speed.