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Methods and apparatus for lancet actuation

Methods and apparatus for lancet actuation description/claims

The present application is a divisional of U.S. Ser. No. 11/735,817, filed Apr. 16, 2007, which is a continuation of U.S. Ser. No. 10/237,261, which is a continuation-in-part of 10/127,395 filed Apr. 19, 2002. The complete disclosure of all applications listed above are incorporated herein by reference for all purposes.

Lancing devices are known in the medical health-care products industry for piercing the skin to produce blood for analysis. Biochemical analysis of blood samples is a diagnostic tool for determining clinical information. Many point-of-care tests are performed using whole blood, the most common being monitoring diabetic blood glucose level. Other uses for this method include the analysis of oxygen and coagulation based on Prothrombin time measurement. Typically, a drop of blood for this type of analysis is obtained by making a small incision in the fingertip, creating a small wound, which generates a small blood droplet on the surface of the skin.

Early methods of lancing included piercing or slicing the skin with a needle or razor. Current methods utilize lancing devices that contain a multitude of spring, cam and mass actuators to drive the lancet. These include cantilever springs, diaphragms, coil springs, as well as gravity plumbs used to drive the lancet. Typically, the device is pre-cocked or the user cocks the device. The device is held against the skin and the user, or pressure from the users skin, mechanically triggers the ballistic launch of the lancet. The forward movement and depth of skin penetration of the lancet is determined by a mechanical stop and/or dampening, as well as a spring or cam to retract the lancet. Such devices have the possibility of multiple strikes due to recoil, in addition to vibratory stimulation of the skin as the driver impacts the end of the launcher stop, and only allow for rough control for skin thickness variation. Different skin thickness may yield different results in terms of pain perception, blood yield and success rate of obtaining blood between different users of the lancing device.

Success rate generally encompasses the probability of producing a blood sample with one lancing action, which is sufficient in volume to perform the desired analytical test. The blood may appear spontaneously at the surface of the skin, or may be “milked” from the wound. Milking generally involves pressing the side of the digit, or in proximity of the wound to express the blood to the surface. In traditional methods, the blood droplet produced by the lancing action must reach the surface of the skin to be viable for testing.

When using existing methods, blood often flows from the cut blood vessels but is then trapped below the surface of the skin, forming a hematoma. In other instances, a wound is created, but no blood flows from the wound. In either case, the lancing process cannot be combined with the sample acquisition and testing step. Spontaneous blood droplet generation with current mechanical launching system vanes between launcher types but on average it is about 50% of lancet strikes, which would be spontaneous. Otherwise milking is required to yield blood. Mechanical launchers are unlikely to provide the means for integrated sample acquisition and testing if one out of every two strikes does not yield a spontaneous blood sample.

Many diabetic patients (insulin dependent) are required to self-test for blood glucose levels five to six times daily. The large number of steps required in traditional methods of glucose testing ranging from lancing, to milking of blood, applying blood to the test strip, and getting the measurements from the test strip discourages many diabetic patients from testing their blood glucose levels as often as recommended. Tight control of plasma glucose through frequent testing is therefore mandatory for disease management. The pain associated with each lancing event further discourages patients from testing. Additionally, the wound channel left on the patient by known systems may also be of a size that discourages those who are active with their hands or who are worried about healing of those wound channels from testing their glucose levels.

Another problem frequently encountered by patients who must use lancing equipment to obtain and analyze blood samples is the amount of manual dexterity and hand-eye coordination required to properly operate the lancing and sample testing equipment due to retinopathies and neuropathies particularly, severe in elderly diabetic patients. For those patients, operating existing lancet and sample testing equipment can be a challenge. Once a blood droplet is created, that droplet must then be guided into a receiving channel of a small test strip or the like. If the sample placement on the strip is unsuccessful, repetition of the entire procedure including re-lancing the skin to obtain a new blood droplet is necessary.

In one aspect of the present invention, a lancet driver is configured to exert a driving force on a lancet during a lancing cycle and is used on a tissue site. The driver comprises of a drive force generator for advancing the lancet along a path into the tissue site, and a sensor configured to detect lancet position along the path during the lancing cycle.

In one embodiment of the present invention, a lancet driver is configured to exert a driving force on a lancet and to be used at a tissue site during a lancing cycle. The driver comprises of a voice-coil, drive force generator, a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle, and a position sensor configured to detect lancet position during the lancing cycle. Although not limited to the following, the voice coil may be a cylindrical coil that goes around the magnet. The voice coil generator may be linear with a flat coil.

In another embodiment of the present invention, a lancet driver is configured to exert a driving force on a lancet during a lancing cycle and to be used on a tissue site. The driver comprises of a voice-coil, drive force generator and a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle. The processor actuates the drive force generator to drive the lancet at velocities in time that follow a selectable lancing velocity profile.

In a further embodiment of the present invention, a lancet driver is configured to exert a driving force on a lancet during a lancing cycle and used on a tissue site. The driver comprises of a housing, a drive force generator; and a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle. The driver further includes a position sensor configured to detect lancet position during the lancing cycle and a human interface on the housing providing at least one output.

In a still further embodiment of the present invention, a body fluid sampling device is configured to exert a driving force on a lancet during a lancing cycle and used on a tissue site. The device comprises of a drive force generator suitable for actuating the lancet along a path towards the tissue site, into the tissue site, and then back out of the tissue site. The lancet penetrates to a depth in the tissue site sufficient to draw body fluid from the tissue site for sampling. The device further includes a closed feedback control loop for controlling the drive force generator based on position and velocity of the lancet.

In another embodiment of the present invention, a body fluid sampling device is provided for use at a tissue site on a patient. The device comprises a drive force generator; a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle, and a position sensor configured to detect lancet position during the lancing cycle. The drive force generator actuates the lancet along a one directional, linear path towards the tissue site, into the tissue site, and then back out of the tissue site. The lancet penetrates to a depth in the tissue site and pauses for a controlled dwell time while in the tissue site. The dwell time may be sufficient to draw body fluid toward a wound channel created by said lancet.

In another embodiment of the present invention, a body fluid sampling device is provided for use at a tissue site on a patient. The device comprises a voice-coil, drive force generator and a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle. The device further includes a position sensor configured to detect lancet position during the lancing cycle. The drive force generator has a magnetic member and a drive coil creating a magnetic field so that the drive coil magnetically attracts the magnetic member. The drive coil may be configured to only partially encircle said magnetic member.

In another embodiment of the present invention, a body fluid sampling device is provided for use at a tissue site on a patient. The device comprises of a voice-coil, drive force generator and a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle. The device further includes a position sensor configured to detect lancet position during the lancing cycle and a mechanical damper disposed to minimize oscillation of the lancet in the tissue site when the lancet reaches an end point of its penetration stroke into the tissue site.

In another embodiment of the present invention, a body fluid sampling device is provided for use on a tissue site. The device further includes a voice-coil, drive force generator and a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle. The device may also include a position sensor configured to detect lancet position during the lancing cycle and a lancet coupler for removably coupling the lancet to said drive force generator.

In another embodiment of the present invention, a body fluid sampling device is provided for use on a tissue site. The device comprises of a housing, a drive force generator, and a processor coupled to the drive force generator capable of changing the direction and magnitude of force exerted on the lancet during the lancing cycle. The device may further include a position sensor configured to detect lancet position during the lancing cycle, a human interface, or possibly include a glucose analyzing device coupled to said housing. The housing and all elements therein have a combined weight of less than about 0.5 lbs.

In another aspect of the present invention, a method is provided for sampling body fluid from a tissue site. The method comprises driving a lancet along a path into the tissue site and using a sensor to detect lancet position along said path into the tissue site. The method may further include stopping the lancet in said tissue site for a controlled dwell time to allow body fluid to gather. In a still further embodiment of the present invention, the method may comprise of driving a lancet along a path into the tissue site using closed loop feedback to control lancet velocity to follow a selectable lancing velocity profile.

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