Abstract:
The present invention is directed to an apparatus and method for positioning a transducer relative to a patient. In one embodiment, a transducer support having a fluid sensing transducer also includes an illuminator coupled to the support to generate visible radiation and to direct the visible radiation along a first optical axis. A reflective surface receives the visible radiation emitted along the first optical axis and directs the visible radiation along a second optical axis and onto an predetermined elevational position on a patient. In another embodiment, a method includes directing visible radiation in a first direction and onto a reflective surface that reflects the visible radiation in a second direction and towards the patient, projecting the visible radiation onto an external portion of the patient to form an illuminated area on the patient, and aligning the transducer with a predetermined elevation on the surface of a patient.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to patient monitoring devices for medical use. In particular, the invention is an apparatus and method for accurately positioning one or more patient monitoring pressure transducers relative to a patient. 
       BACKGROUND OF THE INVENTION 
       [0002]    Blood pressure is the most common index of cardiovascular performance presently known. In general, two methods are used to measure and/or monitor blood pressure. A commonly used non-invasive blood pressure measurement method employs a sphygmomanometer to compress an artery and a stethoscope to detect audible characteristics associated with blood flow while the compression of the artery is reduced to allow blood to flow through the artery. In contrast, invasive blood pressure measurement methods generally involve direct intra-corporeal measuring and monitoring of blood pressure. 
         [0003]    For critically-ill patients, invasive blood measurement methods are favored for several reasons. First, a blood pressure determination using an invasive method greatly enhances the accuracy of the blood pressure determination, since the measurement is not dependent on sphygmomanometer cuff placement or the detection of an audible characteristic. Additionally, an invasive blood pressure determination allows the blood pressure of the patient to be monitored continuously, as opposed to an intermittent measurement using a non-invasive method. An invasive blood pressure determination also permits the rapid detection of any change in the cardiovascular activity of the patient, which may be critically important in emergency situations. Moreover, invasive blood measurement methods may also be used to monitor the blood pressure at selected internal locations within the body of a patient. For example, it is often advantageous to measure and monitor the blood pressure within the chambers of the heart. 
         [0004]    Invasive blood pressure measurement and monitoring generally involves the insertion of a catheter into a selected blood vessel. For example, when it is desired to measure and monitor arterial blood pressure, the catheter is inserted into a radial artery. Correspondingly, if it is desired to measure and monitor venous blood pressure, the catheter may be inserted into the antecubital, radial, tubular or subclavian vein. In any event, the catheter is first filled with a sterile saline solution and de-bubbled. A hypodermic needle is then inserted into the selected blood vessel, and the catheter is then threaded through the hypodermic needle and directed along the blood vessel until the tip of the catheter is positioned at a location where the blood pressure measurement is desired. When the catheter is suitably positioned, the needle may be removed, and the opening may be taped to secure the catheter tip at the selected location. The opposing end of the catheter is coupled to pressure tubing that is also similarly filled with a saline solution. The pressure tubing is then coupled to a pressure transducer capable of detecting pressures transmitted from the selected blood pressure location within the patient. The pressure transducer is, in turn, coupled to an external blood pressure monitoring device and/or other devices, such as a visual display that permits the blood pressure waveform of the patient to be viewed. 
         [0005]    The accuracy of an invasive blood pressure determination using the foregoing method depends upon the careful vertical alignment of the pressure transducer with the vertical position of the catheter tip lodged within the patient. If, for example, the pressure transducer is located at a position below the catheter tip, the indicated blood pressure will be higher than the patient&#39;s actual blood pressure. Correspondingly, if the pressure transducer is located at a position above the catheter tip, the indicated reading will be lower than the patient&#39;s actual blood pressure. Accordingly, careful alignment of the transducer with the vertical position of the catheter tip is a critical concern in blood pressure determinations. 
         [0006]    In one prior art method, the pressure transducer is adjustably positioned on a vertical support, and a leveling device such as a carpenter&#39;s level is positioned between the patient and the pressure transducer. The position of the transducer on the support is then vertically adjusted so that it is approximately level with a reference mark placed on an external portion of the patient&#39;s body. Although the foregoing method is effective, it nevertheless exhibits numerous shortcomings. For example, a variety of equipment is often positioned around the patient that may preclude the use of a generally unwieldy leveling device, such as the carpenter&#39;s level. In another prior art method, as disclosed in U.S. Pat. No. 5,280,789 to Potts, a vertical alignment device is disclosed that may be removably attached to a transducer mounting bracket. The device includes a laser light source that projects a coherent beam of light outwardly towards a patient The transducer mounting bracket is then vertically adjusted until a light spot from the laser source is aligned with a reference mark positioned on an exterior portion of the patient. Although the disclosed device constitutes a significant improvement in the state of the art, it discloses the projection of only a single point of light onto the patient, which may be difficult for persons attending the patient to locate in conditions of elevated ambient light and/or conditions where the vertical alignment device is substantially misaligned with the reference mark on the patient when the device is set up. Additionally, the disclosed device does not permit the beam to be positioned independently of the mounting bracket. 
         [0007]    In yet another prior art device, as disclosed in U.S. Pat. No. 6,071,243 to MacEachern, another vertical alignment device is disclosed that similarly uses a laser to illuminate a reference mark positioned on a patient. The disclosed device, however, similarly projects a single point of light, and accordingly has many of the shortcomings present in the foregoing prior art device. The disclosed device similarly does not permit the beam to be directed independently relative to the vertical alignment device. 
         [0008]    What is needed is a patient monitoring system having a leveling device that may be conveniently aligned with a desired position on a patient so that a pressure transducer may be accurately vertically aligned. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed to an apparatus and method for accurately positioning one or more patient monitoring pressure transducers relative to a patient. In one aspect, the apparatus includes a transducer support configured to support at least one fluid sensing transducer, an illuminator coupled to the support to generate visible radiation and to direct the visible radiation along a first optical axis. A reflective surface is positioned adjacent to the illuminator to receive visible radiation emitted along the first optical axis and to direct the visible radiation along the second optical axis and onto an predetermined elevational position on a patient. In another aspect, the apparatus includes a transducer mount supporting at least one transducer, the mount being movable relative to a selected elevational location in the patient, and an illuminator that generates a beam of visible radiation defining an optical path extending from a illumination source to a surface of the patient. A reflector is positioned in the optical path to receive the beam of visible radiation and to direct the beam in a second direction. In still another aspect, a method includes directing visible radiation in a first direction and onto a reflective surface that reflects the visible radiation in a second direction and towards the patient, projecting the visible radiation onto an external portion of the patient to form an illuminated area on the patient, and aligning the transducer with a predetermined elevation on the surface of a patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an isometric view of a patient monitoring system according to an embodiment of the invention. 
           [0011]      FIG. 2  is a partial cutaway view of the transducer support showing an illuminator according to another embodiment of the invention. 
           [0012]      FIG. 3  is a partial cutaway view of the transducer support showing an illuminator according to still another embodiment of the invention. 
           [0013]      FIG. 4(   a ) through  4 ( e ) are images formed by the embodiment of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present invention is generally directed to an apparatus and method for patient monitoring devices for medical use, and more particularly, to an apparatus and method for accurately positioning one or more patient monitoring transducers relative to the patient. Many of the specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1 through 4  to provide a thorough understanding of such embodiments. One skilled in the art will understand, however, that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
         [0015]      FIG. 1  is an isometric view of a patient monitoring system  10  according to an embodiment of the invention. The system  10  includes a transducer support  12  configured to be attached to a vertical support  14 , such as an IV stand, or other similar vertical support devices. The transducer support  12  is removably attached to the vertical support  14  so that the transducer support  12  may be translated along a length of the vertical support  14  in a direction V and further includes a clamping device  16  to retain the transducer support  12  in a selected position on the vertical support  14 . The transducer support  12  is also configured to support a pressure transducer  18  capable of measuring and monitoring the blood pressure of a patient  20 . Although the transducer support  12  shows a single transducer  18  mounted thereon, one skilled in the art will readily understand that more than one pressure transducer  18  may be supported by the transducer support  12 , so that blood pressure monitoring and measurement may occur simultaneously at more than a single position within the body of the patient  20 . The transducer  18  is coupled to a pressure tube  22  that extends from the transducer  18  to a distal end of a catheter  24 . The apical tip (not shown) of the catheter  24  is inserted into the patient  20  and extends into the patient  20  to a desired location. A vertical location of the apical tip of the catheter  24  is indicated by a target  26  that may be placed externally on the patient  20 . The transducer  18  is further coupled to a saline bag  28  through a saline tube  30  and a flow valve  32  to allow the pressure tube  22  and the catheter  24  to be purged with a saline solution. Line restrictors  31  positioned on the saline tube  30  and the pressure tube  22  may be used to assist in the purging process. The pressure transducer  18  is electrically coupled to a monitoring device  26  configured to process signals received from the pressure transducer  18  and to generate a visual image of the blood pressure level if desired. 
         [0016]    Still referring to  FIG. 1 , the transducer support  12  further includes an illuminator  34  capable of projecting a light beam  36  outwardly from the transducer support  12  and towards the patient  20 . In one particular embodiment, the transducer support  12  includes an illuminator  34  that projects a linear beam  36  towards the patient  15  that may further be rotated about an axis R so that the beam  36  may be swept through an angle A. In another particular embodiment, the transducer support  12  includes an illuminator  34  that may include beam forming optics so that a line  38 , or an image  39  may be projected onto the patient  15 . The foregoing embodiments will be described in greater detail below. 
         [0017]      FIG. 2  is a partial cutaway view of the transducer support  12  of  FIG. 1  showing an illuminator  40  according to another embodiment of the invention. The illuminator  40  includes an illumination source  42  that is mounted within the transducer support  12  so that the light beam  36  is directed in a vertical direction V and into a reflective prism  44  that reflects the beam  36  in a direction that is approximately perpendicular to the direction V. The reflective prism  44  may include a reflective material disposed on a surface of the prism  44  to reflect the beam  36 . Alternately, the prism  44  may be formed so that it includes a surface approximately equal to the critical angle so that the prism  44  becomes internally reflective. In either case, the prism  44  is fixedly positioned on a mount  46  having a centrally disposed aperture  48  that is substantially in alignment with the beam  36 . The mount  46  is rotatably coupled to the transducer support  12  so that the prism  44  may be rotated in a direction R so that the beam may be swept through an angle A, as shown in  FIG. 1 . The mount  46  may be configured so that the rotation of the mount  46  is limited to a rotate through an angle of less than 360 degrees so that the projection of the beam  36  is confined to a predetermined angular range. Alternately, the mount  46  may be configured so that the beam  36  may be continuously rotated through an angle of 360 degrees. Although  FIG. 2  shows a prism  44  that reflects the beam  36  towards the patient  20 , one skilled in the art will readily recognize that other reflective devices having a reflective surface are well known, and may be used instead of the prism  44 . 
         [0018]    Still referring to  FIG. 2 , the illumination source  42  may include an incandescent light source, but preferably includes a coherent light source such as a semiconductor diode laser capable of continuous wave (CW) operation. In one aspect, the diode laser may have a wavelength of about 635 nm. One suitable diode laser is the LD-635-51 diode laser available from Lasermate Group, Inc. of Pomona, Calif. although other alternative diode laser devices exist. The illumination source  42  may also include an optical device  50  that is positioned between the source  42  and the prism  44  to further condition the beam  36 . In one aspect, the optical device  50  may comprise a collimating lens coupled to a diode laser. The illumination source  42  may be coupled to a controller  52  that is further coupled to a power source  54  that may be connected to the controller  52  by means of a manually-actuated switch  56 . A manually-adjustable potentiometer  58  may also be coupled to the controller  52  that permits the intensity of the beam  36  to be controlled when the illumination source  42  is energized. The controller  52  may also be coupled to a pilot lamp  59  that illuminates when the illumination source  42  is energized, so that the operation of the illuminator  40  is readily apparent. 
         [0019]    The foregoing embodiment advantageously permits a beam from the illuminator to be independently directed so that the beam may be swept through a predetermined angular range. Accordingly, the foregoing embodiment allows the beam to be more conveniently directed towards a patient without requiring the vertical support to be moved. 
         [0020]      FIG. 3  is a partial cutaway view of the transducer support  12  of  FIG. 1  showing an illuminator  60  according to another embodiment of the invention. Many of the details of the present embodiment are discussed in detail in connection with  FIG. 2  and in the interest of brevity, will not be discussed further. As in the previous embodiment, the illuminator  60  includes an illumination source  42  that is mounted within the transducer support  12  so that the beam  36  is vertically directed as it emanates from the illumination source  42 . The illuminator  60  further includes a prism  44  that may be held in a fixed relationship relative to the support  12  by a mount  62 . The illumination source  42  is coupled to an image-generating optical element  64  that generally diffracts the beam  36  generated by the illumination source  42  to produce a pre-selected image  39  when projected onto an external portion of the patient  20  (see  FIG. 1 ). Referring now to  FIG. 4 , the pre-selected image  39  may include a linear array of dots, as shown in  FIG. 4(   a ) or a line of predetermined length, as shown in  FIG. 4(   b ). Other image-generating optical elements  64  may be employed to produce still other images. For example, an element  64  may be used to produce a cross-hair pattern, as shown in  FIGS. 4(   c ) through ( e ) when the beam  36  is projected onto an external portion of the patient  15 . Referring to  FIG. 3 , image-generating optical elements  64  suitable for forming the images as shown in  FIGS. 4(   a ) through  4 ( e ) are the L50 Series diffractive pattern generators available from Lasermate Group, Inc. of Pomona, Calif. although other suitable image-generating optical elements exist. 
         [0021]    The foregoing embodiment advantageously allows the light projected from the illumination source to be easily detected by projecting an image onto the patient while the device is being leveled. As noted earlier, finding a single light dot under conditions of elevated ambient light may be difficult, particularly in situations where the projected beam in substantially misaligned with the patient. 
         [0022]    Although the foregoing has discussed pressure measurement within the specific context of invasive blood pressure measurement, it is understood that the foregoing is also applicable to pressure measurements in other regions of the body. For example, the various embodiments of the present invention may, without significant modification, be used to measure and monitor the intercranial pressure in a patient. Additionally, from the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. For example, certain features shown in the context of one embodiment of the invention may be incorporated in other embodiments as well. Accordingly, the invention is not limited by the foregoing description of embodiments except as by the following claims.