| Method and instrument for automated measurement of skin perfusion pressure -> Monitor Keywords |
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  Method and instrument for automated measurement of skin perfusion pressureRelated Patent Categories: Surgery, Diagnostic Testing, Cardiovascular, Measuring Blood Flow In Body Portion Other Than HeartThe Patent Description & Claims data below is from USPTO Patent Application 20060058690. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims the benefit under 35 USC 119(e) of U.S. Patent Application No. 60/609,175, filed Sep. 10, 2004, the entirety of which is hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an instrument for the automated measurement of skin perfusion pressure of a local or regional body site. More particularly the invention relates to an instrument for the automated measurement of skin perfusion pressure that detects and rejects motion artifact. [0004] 2. Description of the Related Art [0005] Skin perfusion pressure measurements are taken to determine whether local blood flow, i.e. capillary perfusion, of a local or regional body site having an ulcer or wound is sufficient to support wound healing. The accurate measurement of this parameter, therefore, is critical to physicians who treat patients suffering from open surface wounds resulting from complications from diabetes, pressure ulcers, burns, accidents, and the like. [0006] Traditionally, skin or surface perfusion pressure is measured utilizing a surface or skin perfusion pressure-monitoring device coupled to a laser Doppler or other type of optical sensor. For example, U.S. Pat. No. 6,178,342 to Borgos et al. discloses a surface perfusion pressure monitor used in conjunction with a laser Doppler probe that measures the "amount" of moving blood contained within a microvascular observation volume in percent tissue hematocrit. This measurement is taken as a function of applied pressure. The laser Doppler optical probe defines an observation volume in the skin near the surface of the patient and a pressure cuff is used to manually apply pressure to the limb near the optical probe. [0007] The laser Doppler sensor is placed against the skin under a pneumatic cuff that is secured to the affected limb, i.e. toe, ankle, arm, leg, etc. A user using an inflation bulb manually inflates the pneumatic cuff. The inflation pressure must be sufficiently high to stop local blood flow at the site of the optical probe. A display instrument is coupled to the optical probe typically via a fiber optic cable, and to the inflation bulb through a tube. Deflation starts and the optical probe monitors the number of moving red blood cells moving into or out of the observation volume without regard to velocity. The number of moving red blood cells detected within the control volume is expressed as a percent and displayed on the display monitor. This value is shown as both a numeric value and a bar graph on the Y-axis. The instrument also measures the pressure within the cuff and displays the applied cuff pressure in millimeters of mercury on the X-axis of the display. A moving bar chart along the X-axis shows the operator which cuff pressure is currently being measured. As pressure is slowly manually released, an indicator of blood flow return is provided in bar chart form. While a technician conducts the test, a physician interprets the data displayed on the display monitor. [0008] Therefore, a significant problem with the use of skin perfusion pressure instruments described by Borgos et al. is that reliable, reproducible measurements are heavily dependent on operator/technician skill and the skill of the physician who interprets the surface perfusion pressure measurement. Another problem associated with manual deflation is that it is sensitive to motion artifact caused by the operator or patient (e.g. patient movement, pressure tubing movement, or sensor movement). In addition, motion artifact may result from patient movement, involuntary muscular movement, operator intervention, and other causes affecting the reading of skin perfusion pressure. If a patient moves the limb to which the sensor/pneumatic cuff is attached, the physician who makes the determination of the pressure at which flow returns might very easily err by reading "motion artifact" as the surface perfusion pressure measurement. When a skin perfusion pressure test is conducted on a sick patient, the physician is already expecting a low value for the surface perfusion pressure measurement. Consequently, given an occurrence of "motion artifact" the physician may interpret it as a skin perfusion pressure reading that is artificially higher than the actual skin perfusion pressure measurement. [0009] For example, illustrated in FIG. 2A is a display from a prior art monitor. As can be seen, measured perfusion rises in percent value as the cuff pressure decreases. The physician conducting the skin perfusion test will likely record the value of skin perfusion pressure as forty-five millimeters of mercury. FIG. 2B again illustrates a display from a prior art monitor with the perfusion measurement rising in percent value as the cuff pressure decreases. However, motion artifact is now displayed at forty-five millimeters of mercury. A physician conducting the skin perfusion test may erroneously record the value of skin perfusion pressure as forty-five millimeters of mercury. [0010] Given the situation described above, there is a need for a system that compensates for, or eliminates, motion-induced artifacts in patient-attached critical care monitoring instruments. In addition, there is a need for a system that increases reliability and reproducibility by eliminating user-created error for example, variable inflation and deflation and/or variable interpretation of the results. A new and improved skin perfusion system that automatically inflates and deflates the pressure cuff, controls inflation and deflation, and detects and rejects motion artifact, and automatically determines an SPP value is needed. SUMMARY OF THE INVENTION [0011] Accordingly it is an object of the present invention to overcome the problems and disadvantages of the surface perfusion pressure instruments of the prior art. It is, therefore, an object of the present invention to automate the measurement of skin perfusion pressure and generate an SPP value. [0012] It is a further object of the present invention to provide a skin perfusion pressure system that automatically inflates and deflates and controls the inflation pressure and deflation rate of cuff pressure. [0013] It is a further object of the invention to provide a skin perfusion pressure monitoring system that automatically detects and rejects motion artifact. [0014] It is a further object of the invention to provide a skin perfusion pressure monitoring system that uses a perfusion sensitive tolerance that progressively adjusts sensitivity thresholds as perfusion returns. [0015] It is a further object of the invention to provide a skin perfusion pressure monitoring system that actively controls the rate of cuff deflation. [0016] It is a further object of the invention to provide a skin perfusion pressure monitoring system that determines when motion is severe enough to affect either the rate of cuff deflation or an accurate determination of an SPP value. [0017] It is a further object of the invention to provide a skin perfusion pressure monitoring system that does not report an SPP value if motion is determined to be too severe or if the resulting SPP waveform does not have a recognizable perfusion signature. [0018] It is a further object of the invention to provide a skin perfusion pressure monitoring system that evaluates duration of perfusion change. [0019] It is a further object of the invention to provide a skin perfusion pressure monitoring system that evaluates the profile of perfusion change. [0020] In a first embodiment of the present invention a skin perfusion pressure monitoring system that automatically calculates the SPP value from perfusion measurements is disclosed. The monitoring system controls and measures cuff pressure and closely controls the rate of cuff deflation during the critical deflation portion of the skin perfusion pressure test cycle. [0021] In another embodiment of the present invention, the monitoring system uses a perfusion sensitive tolerance that progressively adjusts sensitivity thresholds as perfusion returns. This allows for measurements of perfusion over a wide dynamic range while being less sensitive to motion transients. [0022] In another embodiment of the present invention, the monitoring system actively controls the rate of cuff deflation and determines when motion is severe enough to affect this rate. The test is ended if motion is determined to be too severe. Continue reading... Full patent description for Method and instrument for automated measurement of skin perfusion pressure Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and instrument for automated measurement of skin perfusion pressure patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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