A medical device for removing tissue from a subject, comprising: a distal housing configured with a tissue cutter assembly; an elongate member coupled to the distal housing and configured to introduce the distal housing to a target tissue site of the subject, the elongate member having an outer tube, an inner drive tube rotatably mounted within the outer tube, and an annular void formed between the inner drive tube and the outer tube, wherein the outer tube and the distal housing form a stator assembly; a coupler located at a distal end of the inner drive tube and rotationally coupled therewith to form a rotor assembly, the coupler configured to engage with the tissue cutter assembly to rotatably drive the tissue cutter assembly, the coupler having a rear thrust surface configured to cooperate with a first surface on the stator assembly to prevent the inner drive tube from moving proximally beyond a predetermined rear location, the coupler having a forward thrust surface configured to cooperate with a second surface on the stator assembly to prevent the inner drive tube from moving distally beyond a predetermined forward location; and a commutator portion located between the rotor assembly and the stator assembly, the commutator portion having at least one solid region (936, 938) configured to rotatably support the rotor assembly relative to the stator assembly, the commutator portion having at least one fluid channel (931, 934) configured to allow passage of a fluid from the annular void, distally across the commutator portion, and into a first fluid plenum adjacent to the rear thrust surface and the first surface of the stator assembly; wherein the coupler and the distal housing form at least one passage therebetween that fluidically connects the first fluid plenum with a second fluid plenum adjacent to the forward thrust surface and the second surface of the stator assembly, wherein the device is configured to allow a fluid to flow distally through the annular void, through the at least one fluid channel in the commutator portion, through the first fluid plenum, through the at least one passage between the coupler and the distal housing, through the second fluid plenum, into at least a portion of the tissue cutter assembly, and proximally through the inner drive tube, wherein the device is configured to allow the fluid to lubricate and cool the forward and rear thrust surfaces and the tissue cutter assembly, and to transport tissue pieces cut by the tissue cutter assembly proximally through the inner drive tube. a distal housing configured with a tissue cutter assembly; an elongate member coupled to the distal housing and configured to introduce the distal housing to a target tissue site of the subject, the elongate member having an outer tube, an inner drive tube rotatably mounted within the outer tube, and an annular void formed between the inner drive tube and the outer tube, wherein the outer tube and the distal housing form a stator assembly; a coupler located at a distal end of the inner drive tube and rotationally coupled therewith to form a rotor assembly, the coupler configured to engage with the tissue cutter assembly to rotatably drive the tissue cutter assembly, the coupler having a rear thrust surface configured to cooperate with a first surface on the stator assembly to prevent the inner drive tube from moving proximally beyond a predetermined rear location, the coupler having a forward thrust surface configured to cooperate with a second surface on the stator assembly to prevent the inner drive tube from moving distally beyond a predetermined forward location; and a commutator portion located between the rotor assembly and the stator assembly, the commutator portion having at least one solid region (936, 938) configured to rotatably support the rotor assembly relative to the stator assembly, the commutator portion having at least one fluid channel (931, 934) configured to allow passage of a fluid from the annular void, distally across the commutator portion, and into a first fluid plenum adjacent to the rear thrust surface and the first surface of the stator assembly; wherein the coupler and the distal housing form at least one passage therebetween that fluidically connects the first fluid plenum with a second fluid plenum adjacent to the forward thrust surface and the second surface of the stator assembly, wherein the device is configured to allow a fluid to flow distally through the annular void, through the at least one fluid channel in the commutator portion, through the first fluid plenum, through the at least one passage between the coupler and the distal housing, through the second fluid plenum, into at least a portion of the tissue cutter assembly, and proximally through the inner drive tube, wherein the device is configured to allow the fluid to lubricate and cool the forward and rear thrust surfaces and the tissue cutter assembly, and to transport tissue pieces cut by the tissue cutter assembly proximally through the inner drive tube.