Ventricular assist device with stabilized impeller
Apparatus and methods are described including a left-ventricular assist device that includes a tube configured to traverse a subject's aortic valve, with a distal portion of the tube within the subject's left ventricle. A frame disposed within the distal portion of the tube defines cells, and a width of each of the cells within a cylindrical portion of the frame is less than 2 mm. An inner lining lines at least some of the cylindrical portion of the frame. An impeller is disposed inside the frame such that a gap between an outer edge of the impeller and the inner lining is less than 1 mm. The impeller is stabilized with respect to the frame, such that, during rotation of the impeller, the gap between the outer edge of the impeller and the inner lining is maintained and is substantially constant. Other applications are also described.
1. Apparatus comprising:
a left-ventricular assist device configured to assist left-ventricular functioning of a subject, the left-ventricular assist device comprising:
a tube configured to traverse an aortic valve of a subject, such that a proximal end of the tube is disposed within an aorta of the subject and a distal end of the tube is disposed within a left ventricle of the subject;
a frame disposed within at least a portion of the tube, the frame defining a plurality of cells, and the frame being configured such that, in a non-radially-constrained configuration of the frame, the frame comprises a generally cylindrical portion, a width of each of the cells within the cylindrical portion, as measured around a circumference of the cylindrical portion, being less than 2 mm;
an inner lining that lines at least some of the cylindrical portion of the frame; and
an impeller disposed inside the frame such that, in a non-radially-constrained configuration of the impeller, at a location at which a span of the impeller is at its maximum, the impeller is disposed within the cylindrical portion of the frame, such that a gap between an outer edge of the impeller and the inner lining is less than 1 mm,
the impeller being configured:
to rotate such as to pump blood from the left ventricle to the aorta, and
to be stabilized with respect to the frame, such that, during rotation of the impeller, the gap between the outer edge of the impeller and the inner lining is maintained and is substantially constant.
2. The apparatus according to claim 1 , wherein the impeller is configured to reduce a risk of hemolysis by being stabilized with respect to the frame, relative to if the impeller were not stabilized with respect to the frame.
3. The apparatus according to claim 1 , wherein the width of each of the cells within the cylindrical portion as measured around the circumference of the cylindrical portion is between 1.4 mm and 1.6 mm.
4. The apparatus according to claim 1 , wherein the width of each of the cells within the cylindrical portion as measured around the circumference of the cylindrical portion is between 1.6 mm and 1.8 mm.
5. The apparatus according to claim 1 , wherein the impeller is configured such that the gap between the outer edge of the impeller and the inner lining is less than 0.4 mm.
6. The apparatus according to claim 1 , wherein:
the left-ventricular assist device further comprises an axial shaft and proximal and distal radial bearings disposed, respectively, at proximal and distal ends of the frame, the axial shaft passing through the proximal and distal radial bearings;
the impeller is coupled to the axial shaft; and
the impeller is stabilized with respect to the frame by the impeller being held in a radially-fixed position with respect to the axial shaft and the axial shaft being rigid.
7. The apparatus according to claim 6 , wherein the impeller comprises bushings that are disposed around the axial shaft, and at least one of the bushings is configured to be slidable with respect to the axial shaft, wherein the impeller is stabilized with respect to the frame by a region along the axial shaft over which the at least one bushing is configured to be slidable with respect to the axial shaft being coated with a coating, such as to substantially prevent the impeller from vibrating by the coating reducing a gap between the at least one bushing and the axial shaft.
8. The apparatus according to claim 6 , wherein the impeller is stabilized with respect to the frame by substantially preventing vibration of the frame with respect to the axial shaft by a ratio of a length of the cylindrical portion of the frame to a total length of the frame being more than 1:2.
9. The apparatus according to claim 8 , wherein the ratio of the length of the cylindrical portion of the frame to the total length of the frame is more than 2:3.