Abstract:
A process and apparatus for measuring pressure buildup in a body compartment that encases muscular tissue. The method includes assessing the body compartment configuration and identifying the effect of pulsatible components on compartment dimensions and muscle tissue characteristics. This process is used in preventing tissue necrosis, and in decisions of whether to perform surgery on the body compartment for prevention of Compartment Syndrome. An apparatus is used for measuring pressure build-up in the body compartment having components for imparting ultrasonic waves such as a transducer, placing the transducer to impart the ultrasonic waves, capturing the imparted ultrasonic waves, mathematically manipulating the captured ultrasonic waves and categorizing pressure build-up in the body compartment from the mathematical manipulations.

Description:
JOINT GOVERNMENT EMPLOYEE AND SMALL BUSINESS OR NONPROFIT CONTRACTOR INVENTIONS 
   The inventions described herein were made as a result of activities undertaken within the scope of a cooperative agreement between the National Aeronautics and Space Administration and the University of California, San Diego, and is subject to the provisions of Public Law 96-517 (35 U.S.C. § 202) and may be manufactured and used by or for the Government for nmental purposes without the payment of any royalties thereon or therefor. In accordance with 35 U.S.C. 202, the contractor elected not to retain title. 

   FIELD OF THE INVENTION 
   The present invention provides novel processes, and apparatus for performing the processes, for interrogating a body compartment for compartment syndrome. 
   BACKGROUND AND DESCRIPTION OF THE RELATED ART 
   Compartment Syndrome, which may cause Volkmann&#39;s Ischemic Contracture, occurs when bleeding and swelling interfere with proper blood circulation in enclosed groups of muscles and nerves. In the body certain muscle groups, along with their associated blood vessels and nerve tissue, are covered by fascia, a noncompliant collagenous membrane, forming what is termed a “compartment.” With bleeding and swelling, compartment pressure (CP) within the compartment increases, causing a decrease in venous, capillary and arterial blood flows. The network of blood vessels in the compartment becomes compressed by the pressure differential between the CP (exterior to the blood vessel) and the blood vessel interior, this impedes the rate of blood volume flow (RBFV) through the blood vessel network. Swelling occurs within the tissue, further restricting the blood flow. Although, according to the well-known Windkessel Theory, an occasional fluctuation in blood pressure pushes a bolus of blood through the blood vessel network, this normally is insufficient to reverse the continual deterioration of the muscle mass or maintain tissue viability. As the RBFV decreases to zero and as CP rises, muscles tend to tighten, contract and deteriorate, with both nerve and muscle cells eventually dying from the lack of nutrients. Compartment Syndrome creates acute pain and a progressive loss of muscle and nerve functions, usually in the lower leg and forearm, or possibly other body areas such as the wrist, buttocks, thigh and upper arm. As pressures build, blood flow becomes blocked, leading to permanent injury (Volkmann&#39;s Contracture) and possible amputation of the limb. 
   Compartment Syndrome most commonly occurs with trauma or substantial injury to the body, such as a broken or crushed arm or leg (frequently resulting in Acute Compartment Syndrome), with some occurrences of Compartment Syndrome coming from tight bandages or surgery (which can result in Acute Compartment Syndrome) or extended exercise (Chronic [exertional] Compartment Syndrome). After trauma to a given area, a person may experience pain or an inability to use the muscles in the injured area. Surgery, such as cutting the fascia, can be performed to decrease the compartment pressure and increase blood flow to the muscle. As the fascia is substantially inelastic, swelling increases pressure within the body compartment, and muscles, blood vessels and nerves within the compartment are compressed. 
   Even experienced physicians can have trouble making a reliable diagnosis of Compartment Syndrome. Known testing for Compartment Syndrome may include pressure measurement in the compartment by inserting a needle attached to a pressure meter. Compartment pressure of greater than 30-45 mmHg or pressures within 30 mmHg of the diastolic blood pressure, indicate the presence of Compartment Syndrome. 
   U.S. Pat. No. 5,746,209 to Yost et al., entitled “Method of and Apparatus for Histological Human Tissue Characterization Using Ultrasound” discloses the use of ultrasound for determining histological characteristics of tissue by converting the return of energy pulses into numerical terms, useful in a diagnosis for the development of pressure ulcers. However, Yost et al. &#39;209 does not address the diagnosis of Compartment Syndrome. 
   There is a need in the art to provide a non-invasive determination of CP associated with Compartment Syndrome. The present invention addresses this and other needs. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention includes a process for measuring CP buildup in one or more body compartments that encase muscular tissue comprising the steps of assessing a body compartment configuration and identifying the effect of pulsatible components on the dimensions/geometry of the body compartment; and the present invention also includes a method for preventing tissue necrosis and an incision, as well as a non-incision product result from this process. 
   The present invention also includes an apparatus for assessing CP build-up in one or more body compartments that encase muscular tissue. This apparatus, depending upon the inventive embodiment being utilized, comprises one or more of the following: (a) a transmitting device for imparting ultrasonic waves into the one or more body compartments, (b) means for positioning the transducer adjacent to the one or more body compartments effective for imparting ultrasonic waves therein, (c) a receiver for capturing a series of reflections of the imparted ultrasonic waves from the interior of the tissue bounded by the compartment fascia, and converting these reflected waves into data, such as electrical signals, (d) means for mathematically manipulating the captured data, and (e) means for categorizing intra-muscular pressure build-up in the one or more body compartments from the mathematical manipulations. 
   In at least one embodiment, the present invention identifies dimensional changes in the blood flow network with pulsatile pressure changes to ascertain whether blood flow is adequate to assure tissue viability. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic representation of apparatus of the present invention; and 
       FIG. 2  is a schematic representation of ultrasonic interrogation of a body compartment of the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The present invention provides a novel process and apparatus for interrogating a body compartment for Compartment Syndrome. Muscle groups in the arms and legs are encased in these body compartments that generally are defined by tubular shaped collagenous membranes as well as bone. At maximum distension the membrane loses compliance to the point that excessive CP can build up within the tissues confined by the membrane. A pathological condition, Compartment Syndrome, can develop because of such excess CP build-up. Body compartments also possess extensive networks of blood vessels, known as blood vessel networks (BVN), which typically obscure non-invasive methods of analysis due to the tubular shaped collagenous membranes. The present invention affords a method and means to ascertain the build-up of excessive pressures in compartments which encase muscle and muscle groups thereby warning medical practitioners of the existence of potentially dangerous medical conditions, which when allowed to persist, generally result in tissue necrosis. 
   The process of the present invention measures CP buildup in one or more body compartments that encase muscular tissue by assessing a body compartment configuration and identifying the effect of pulsatible components (from the blood flow) on the dimensions of the body compartment. As seen in  FIG. 1 , the present invention includes an apparatus  10  for measuring pressure build-up in one or more body compartments  20  that encase muscular tissue. Referring to the schematic of  FIG. 1 , a representative equipment arrangement of the apparatus  10  in operation is shown. The apparatus  10  of the present invention includes a transducer  40  as a means for imparting ultrasonic waves  30  through the skin  22  (shown in  FIG. 2 ), overlaying the body compartment  20 . The transducer  40  includes a device by which energy can flow from one or more transmission systems to one or more other transmission systems. Transducer imparting devices  40  of the present invention may include a variety of known devices, for example, a broadband ultrasonic transmit/receiver transducer, pure-tone ultrasonic transmit/receiver transducer, and combinations thereof. 
   Referring now to  FIG. 2 , the transducer  40  is positionally located in a manner for effectively interrogating a body compartment  20  for Compartment Syndrome characterization thereof. Placement of the transducer  40  positions the release (imparting) of ultrasonic waves  30  into the body compartment  20  for obtaining relevant data related to the body compartment  20  from reflections  32  of the imparted ultrasonic waves  30  ( FIG. 1 ). The means for effectively positioning the transducer  40  to obtain data from the reflections  32  of the imparted ultrasonic waves  30  allows capture of the reflected ultrasonic waves  32  from the body compartment  20 , and retention and manipulation of data contained therein. One method of positioning the transducer  40  relative to the body compartment  20  includes placing the ultrasonic transducer  40  against the skin  22  of the extremity using a gel medium  48  for attaching the ultrasonic transducer  40  to the skin  22  adjacent to the body compartment  20 . The gel medium  48  may serve as a couplant, and if needed, may be used to make a delay line for the ultrasonic wave transmission. Gel mediums  48  may include viscous substances that temporarily adhere the transducer  40  to the skin  22 , such as those commonly known as ultrasound coupling gels. Additionally, for mechanical stability the transducer  40  may be inserted into the center of a disk  50 , which can be taped, or otherwise secured, to a patient. 
   As seen in  FIGS. 1 and 2 , with the placement of the transducer  40  on the skin  22 , and the generation of ultrasonic waves  30  into the body compartment  20 , the imparted ultrasonic waves  30  are reflected ( 32 ) as they impinge on different surface layers within, and outside of, the body compartment  20 , such as the compartment boundaries  26 , identified as upper boundary  26 A and lower boundary  26 B, or BVN  24 . The body compartment  20  may be placed at maximum distension prior to assessing the body compartment  20  configuration. As shown, the ultrasonic transducer  40  is further connected to a pulser-receiver system  42 , with an appropriate electronics package, for fully utilizing the ultrasonic transducer  40  to investigate for Compartment Syndrome. Referring again to  FIG. 1 , these reflected waves  32  are captured for analysis by the pulser receiver  42  as a means to capture the reflected waves  32 . Additionally, the means for capturing the imparted ultrasonic waves  30  may include any appropriate retention means  44 , generally suited to a specific medical purpose. Representative retention means  44  include, for example without limitation, data storage, data display, data transmission, data analysis and/or combinations thereof. For example, emergency triage teams may use data display and/or data transmission to address urgent medical needs. Therapeutic centers may primarily use data comparisons for monitoring treatments. Data storage is preferably used in most medical situations for training, medical review and/or trend analysis. Computer manipulations, storage and other data methodologies using computer and data storage devices  46 , or other like devices, may include data prior to, during and/or after mathematical manipulations, detailed below, are performed on the captured data. In at least one embodiment, the retention means  44  includes a digital oscilloscope with fast Fourier Transform capability detailed below. 
   The data obtained from the captured reflected ultrasonic waves  32  are mathematically manipulated to differentiate the separate layers of the body, both inside and outside of the body compartment  20 . Mathematical manipulations include organization and processing of the data in any appropriate manner that defines these layers. Preferably, the mathematical manipulation of the captured ultrasonic waves includes Fourier Transform manipulation. The Fourier Transform manipulations of the data allow categorization of pressure build-up in the interrogated body compartment. As Compartment Syndrome is most prevalent in arms and/or legs, these body masses are typically investigated, although other body compartments  20  also may be interrogated for pressure buildup. Aspects of tissue characterization are described in U.S. Pat. No. 5,746,209 to Yost et al., entitled “Method of and Apparatus for Histological Human Tissue Characterization Using Ultrasound,” the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. 
   With the transducer  40  positioned on, and transmitting ultrasonic waves  30  into, the skin  22 , body compartments  20  are interrogated with the capture of the reflected ultrasonic waves  32 . The apparatus  10  of the present invention can include either identifying a decrease in the captured imparted ultrasonic waves or identifying a ratio of low-frequency amplitudes to high frequency amplitudes present in the mathematical manipulation of the captured ultrasonic waves for categorization of the CP build-up. 
   In operation, as shown, the transducer  40  is energized with an electrical pulse which generates the ultrasonic pulse (UP) incorporating the ultrasonic wave  30 . The UP  30  travels through the skin  22  and into the underlying tissues in the region of the compartment  20  as well as through the compartment  20 , into the tissues contained by the compartment  20 . Reflections  32  occur at each impedance discontinuity  32   a ,  32   b ,  32   c ,  32   d , or each tissue interface, and are received at the transducer  40  in the sequence which they occur. The transducer  40  converts the ultrasonic sequence received back from the segment into an electrical sequence which can be amplified and sent to the oscilloscope to be digitized and displayed. For simplicity and speed of processing, the scope can perform and display the Fast Fourier Transform (FFT) on the sequence. Of note, the sequence and reflected sequence are partially regular over this segment, with this regularity showing on the FFT as a relatively larger amplitude of received signal at some specific frequency f 1 . With the pressure in the compartment  20  within normal limits, the regularity of the sequence will be perturbed during heart beats, with this perturbation causing a change in the amplitude at f 1 , indicating blood flow in the muscle tissue at those blood vessels which give rise to the constructive interference shown as a peak in the Fourier transform. If the pressure in the compartment  20  is sufficiently high, then flow through the BVN is impeded. During this condition the long term regularity is increased, and more peaks become prominent especially at the lower frequencies. Occasionally, and momentarily, the order disappears from the FFT, only for the order to return. This permits the Windkessel condition to be identified and timed. If these disturbances are non-existent, or occur too infrequently, then tissue viability is at risk, and surgical intervention may be needed. 
   The FFT and the temporal sequence can be stored for future reference and for interpretation. The system may be set in an algorithm which automatically identifies the conditions. The system may be incorporated into a monitor which would be capable of logging the circulation condition within a compartment, and placed within a system for scanning to explore the state of circulation within the compartment. 
   In one embodiment, determination of the presence or absence of Compartment Syndrome occurs with identification of the BVN and the effect of pulsatile components on the geometry of the BVN. Operation of the Fourier Transform manipulations provides identification of the net geometry through the pulsating frequency components. An analysis based on the pulsating components showing a decrease or diminishment of the pulsations indicates a pressure build-up. 
   In another embodiment, a time-reversal technique is incorporated as a means to identify changes in the compartment as blood vessel pulsations occur. As the broadband ultrasonic transducer  40  is activated with a voltage spike, the received signal is recorded and then reversed in time and played back to the transducer  40 . The new signal received from the time-reversed signal from the previous step produces a spike, when received, unless there has been a change in the body compartment  20 . As such, by monitoring the reversed play-back signal and noting variations from the spike, changes in compartment dynamics affecting the shape of the spike can be identified. Shape changes in the spike become readily identifiable and can be analyzed through mathematical manipulations, such as FFT. With the absence of Compartment Syndrome, the spike provides a flat FFT. Hence by noting variations in the FFT, changes in conditions within the body compartment  20  are identified, and a practitioner monitoring for Compartment Syndrome may be alerted. Additional analysis of the FFT of the spike permits the determination of the type of change that could occur, and/or has occurred in the compartment  20 . 
   Using the inventive processes for monitoring the indication of CP buildup, prevention of tissue necrosis is possible. With the determination of the presence of Compartment Syndrome, corrective or preventive actions may be performed, such as cutting (slitting) the fascia to relieve the excessive CP. Conversely, when the absence of compartment syndrome is determined, detrimental actions such as cutting an incision may be avoided. This non-incision determination prevents unnecessary medical treatment, further benefiting the muscle function and health of a patient. 
   The foregoing summary, description, and examples of the present invention are not intended to be limiting, but are only exemplary of the inventive features which are defined in the claims.