Abstract:
A flexible finger sensor having a finger entrance, a sensor holder at a distal end of the assembly, and a fenestrated region disposed between the finger entrance and the sensor holder. A displacement resistant finger sensor and method of use for reducing motion-related artifacts by mechanical isolation from external forces by providing a resilient sensor body having a digit entrance, a sensor holder, and a fenestrated region between the digit entrance and the sensor holder. The sensor holder maintains sensing elements relative to a user&#39;s finger, with said sensing elements being in communication with a monitoring device via a lead wire. The lead wire may extend at a lateral edge of the sensor body. A force to the lead wire may be applied so as to distort the fenestrated region without substantially disturbing the sensing elements relative to the finger surface.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to physiological sensors. More specifically, the present invention relates to a fingertip sensor adapted to improve sensor stability in order to minimize the occurrence of motion-induced artifacts within a physiologic signal. 
     BACKGROUND OF THE INVENTION 
     Non-invasive physiological monitoring is a common means for testing, detecting, and treating a physiological condition. Typically, non-invasive monitoring techniques such as pulse oximetry, electrocardiography (ECG), electroencephalography (EEG), and ultrasonic imaging, to name a few, require that a sensor be placed in direct contact with a patient undergoing the procedure. 
     Pulse oximetry involves the non-invasive monitoring of oxygen saturation level in blood-profused tissue indicative of certain vascular conditions. In practice, light is passed through a portion of a patient&#39;s body which contains arterial blood flow. An optical sensor is used to detect light which has passed through the body, and variations in the detected light at various wavelengths are then used to determined arterial oxygen saturation and/or pulse rates. Oxygen saturation may be calculated using some form of the classical absorption equation know as Beer&#39;s law. 
     Accurate measurement of oxygen saturation levels are predicated upon optical sensing in the presence of arterial blood flow. A finger provides a convenient access to a body part through which light will readily pass. Local vascular flow in a finger is dependent on several factors which affect the supply of blood. Blood flow may be affected by centrally mediated vasoconstriction, which must be alleviated by managing the perceived central causes. Peripheral constriction via external compression, however, can be induced by local causes. One such cause of local vasococompression is the pressure exerted by the sensor on the finger. Many currently available pulse oximetry finger sensors have a hard shell which has a high profile and is maintained on the finger by the action of a spring. Since excess pressure on the finger can dampen or eliminate the pulsation in the blood supply to the finger, these springs are intentionally relatively weak. The result of this compromise is that the spring-held sensors readily fall off the finger. It is desirable for a finger sensor to be retained on the finger with only slight pressure, while at the same time being immune to easy dislocation. 
     Non-disposable finger sensors typically utilize a clamp design for retaining the sensor on the finger. Such devices generally consist of a small spring-loaded clip which attaches to the finger tip in a manner similar to a common clothespin. 
     Many known non-disposable sensors are relatively bulky. The prior art sensors with their high profile exhibit a relatively high inertia of the housing relative to the finger. This results in a susceptibility to relative motion between the sensor and the finger as the finger is moved. This relative motion manifests itself as motion artifacts in the detected signal. It would be desirable for a finger sensor to be as light as possible so as to minimized relative inertial motion between the sensor and the finger. 
     Motion artifacts caused by displacement of the lead wire are especially problematic for oximetric sensors. Common oximetric finger sensors often locate the lead wire from the sensor over a central portion of a patient&#39;s finger. When the patient flexes or curls his finger, it is common for the lead wire to pull against the sensor causing the light elements to be displaced. 
     Consequently, there is a need in the art for a sensor assembly which is capable of mechanically isolating a sensor holder without the need to tightly secure the sensor to the patient. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a sensor assembly which provides improved mechanical isolation between the sensor holder region and other regions of the sensor assembly. In one embodiment, the sensor assembly includes a collar, a fenestrated region, a sensor holder, and a sensor. The collar, the fenestrated region, and the sensor holder are preferably made of a flexible material, such as a polymer. The sensor can include any known sensors used for monitoring of physiological parameters. 
     In one embodiment of the invention, the collar defines an entrance into the sensor assembly. In one embodiment, a strain relief extends generally perpendicularly to the collar and is located near a lateral side of the sensor assembly. The strain relief cooperates with the collar to define a pathway for a lead wire which connects the sensor to a physiological monitor. 
     In one embodiment, the fenestrated region includes a plurality of bridges separated by windows. The fenestrated region may additionally be of a reduced thickness compared to other portions of the sensor assembly. In another embodiment of the invention, the fenestrated region can include one relatively large opening in the sensor assembly. The fenestrated region may respond to external forces transferred through the collar by substantial deformation, including stretching, twisting, buckling and bending. As a result, the fenestrated region contributes to mechanical isolation of the sensor holder from the collar. Consequently, when a force is applied to the collar, the relatively thin fenestrated region is able to stretch or distort without disrupting the sensor holder. The fenestrated region which can include one or more fenestrations or openings into the interior of the sensor assembly, promotes an increase in user comfortability and digit ventilation. The fenestrated region is optional and embodiments of the present invention may be device of one or more fenestrations. 
     In one embodiment, the sensor holder provides seats wherein portions of the sensor element is received. The seats are positioned such that the sensor element is optimally located with respect to the patient. A finger stop and guide may be provided within an interior of the finger assembly in order to facilitate the positioning of the finger relative to the sensor element. 
     In one embodiment, an elongated pleat extends across each lateral side of the sensor assembly. The pleats enable the sensor assembly to expand and accommodate a variety of finger sizes. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS AND FIGURES 
       For purposes of facilitating and understanding the subject matter sought to be protected, there is illustrated in the accompanying drawings an embodiment thereof. From an inspection of the drawings, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. 
         FIG. 1  is a perspective view of a first embodiment of a finger assembly according to the present invention. 
         FIG. 2  is a top plan view of the finger assembly of  FIG. 1 . 
         FIG. 3  is another perspective view of the finger assembly of  FIG. 1   
         FIG. 4  is a cross-sectional view of the finger assembly of  FIG. 2  taken along lines B-B. 
         FIG. 5  is a cross-sectional view of the finger assembly of  FIG. 2  taken along lines A-A. 
         FIG. 6  is a cross-sectional view of the finger assembly of  FIG. 2  taken along lines C-C. 
         FIG. 7  is a perspective view of another embodiment of the present invention. 
         FIG. 8  is a perspective view of another embodiment of the present invention. 
         FIG. 9  is a perspective view of another embodiment of the present invention. 
         FIG. 10  a perspective view of another embodiment of the present invention. 
         FIG. 11  is a perspective view of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In one embodiment of the present invention, as shown in  FIGS. 1-6 , a finger sensor assembly  10  is provided which mechanically isolates the sensor elements relative to other portions of the sensor assembly  10  in order to minimize inadvertent displacement of the sensor elements caused by external forces. For the purposes of explanation only, the present invention is disclosed utilizing an embodiment that is configured for the measurement of oxygen saturation through known oximetric transmittance techniques. As one skilled in the art can readily appreciate, the present invention is easily adaptable to accommodate a number of different physiological monitoring applications and configurations, including but not limited to, other optical sensors, reflective sensor, etc. 
       FIG. 1  illustrates an embodiment of the assembly  10  adapted as an electro-optical sensor for a fingertip. In the illustrated embodiments, sensor assembly  10  is utilized within a system including a monitoring unit (not shown) for oxygen saturation measurement. Sensor assembly  10  preferably includes a molded polymeric body defining a collar  12 , a fenestrated region  14 , and sensor holder  16 . As illustrated in  FIG. 5 , sensor assembly  10  further includes an oximetric sensor having one or more LED&#39;s  18  and one or more photodetectors  20  and being connected to the monitoring unit via a lead wire  22 . The oximetric sensor can also or alternatively contain other known components utilized in the measurement of oxygen saturation. 
     As shown in  FIGS. 1 and 3 , collar  12  defines an entrance into an interior of the sensor assembly  10 . The collar  12  defines internal surfaces  26 ,  28  which are shaped to comfortably conform to the top and bottom surfaces of a human digit. The collar  12  is preferably substantially thicker than either the fenestrated region  14  or sensor holder  16 . The molded shape and thickness of collar  12  enable it to comfortably engage the human digit. As illustrated in  FIG. 5 , collar  12  extends in a longitudinal direction and has a length L c . The sensor assembly has an overall length, L. 
     The illustrated embodiment of sensor assembly  10  includes a strain relief  30  extending away from collar  12 . The strain relief  30  defines an internal passageway  32  in communication with the interior of assembly  10 . The strain relief  30  and collar  12  together define a pathway for a lead wire  22 . In one preferred embodiment, the strain relief  30  is positioned near a lateral side of the collar  12 . As described in more detail hereinafter, by so positioning the lead wire  22  near a lateral side of collar  12  the deleterious effects of external forces applied to lead wire  22  may be minimized. In the illustrated embodiment, strain relief  30  is positioned between the longitudinal centerline and the lateral edge of the sensor assembly  10 . In other embodiments of the present invention, the strain relief  30  may be positioned further away from the centerline. 
     The fenestrated region  14  includes one or more fenestrations such as openings, windows, holes, perforations and/or slits. The fenestrations contribute to the mechanical isolation of the sensor holder  16  from the collar  12  by permitting the fenestrated region  14  to undergo substantial deformation or displacement relative to its relaxed state without displacing the sensor holder  16 . In one embodiment, the fenestrated region  14  is preferably thinner than both the collar  12  and the sensor holder  16 . As a result, the relatively thin fenestrated region  14  is able to deform in response to an external forces (transferred through collar  12  and/or sensor holder  16 ) while minimizing disturbances transferred to the sensor holder  16 . 
     In the embodiment of  FIGS. 1-6 , the fenestrated region  14  includes a plurality of elongated bridges  40  which connect the collar  12  to the sensor holder  16 . Each bridge  40  includes a plurality of resilient, laterally extending folds  42  which facilitate buckling or expansion of the bridges  40  in response to external forces transferred through lead wire  22 . A plurality of openings  44  are defined between the bridges  40 . As illustrated in  FIG. 5 , fenestrated region  14  extends in a longitudinal direction and has a length L fr . Openings  44  of the illustrated embodiment are generally unobstructed. In other embodiments of the present invention, openings  44  may include a screen, mesh or fabric structure. For example, the fenestrations of the embodiment of  FIG. 8  are defined by a screen element  50 , and the embodiment of  FIG. 7  includes a plurality of small holes  52  defining the fenestrations.  FIG. 9  illustrates a finger sensor assembly  10  according to the present invention which lacks a fenestrated region. In place of the fenestrated region, an area of reduced thickness  58  is defined between the collar  12  and the sensor holder  16 . As another alternative,  FIG. 10  illustrates a finger assembly  10  having a single relatively large opening or fenestration  44  on each side. 
     Referring particularly to  FIG. 5 , preferably the length of the collar, L c , is between 5% to 35% of the overall length of sensor assembly  10 , L, and the length of the fenestrated region, L fr , is between 20% to 50% of sensor  10  length, L. In a preferred embodiment, the length of the fenestrated region, L fr , is approximately 35% of sensor length, L, and the collar length, L c , is approximately 20% of sensor  10  length, L. 
     The sensor assembly  10  defines an expandable interior for receiving the user&#39;s finger. In the illustrated embodiments, the sensor assembly  10  includes a finger seat  54  and finger stop  56  for engaging the finger and thereby locating the sensor elements relative to the nail region of the user. The sensor holder  16  is adapted to align the sensor elements  18 ,  20  in position relative to a finger surface. Preferably, sensor holder  16  includes a finger seat  54  which functions to orient the sensor assembly  10  relative to a human digit so that sensor elements  18 ,  20  are optimally positioned relative to a finger surface. One skilled in the art will readily appreciate that the sensor holder  16  is easily reconfigured so that the seat  54  and/or stop  56  may be positioned or shaped to accommodate the needs of a particular sensor. 
     In the illustrated embodiments of the present invention, a pleat structure  60  extends along each opposing lateral side of the sensor assembly  10 . The pleat structure  60  expands to allow the finger assembly  10  to accommodate a variety of differently sized fingers. Pleat structure  60  may include one or more folds of material. In other embodiments of the present invention (not shown), pleat structure  60  may be differently configured and/or limited to the collar  12  and/or sensor holder region  16 . 
     Lead wire  22  may include one or more conductive wires or may include a light conducting fiber (not shown). In a preferred embodiment, a portion of lead wire  22  is maintained within the interior of the sensor assembly  10 . That portion of the lead wire  22  within the sensor assembly  10  may be a conductive wire, a flexible conductive sheet, or another conductive element having a different configuration. Those of ordinary skill in the art will appreciate a variety of different ways to route portions of the lead wire  22  from the strain relief structure  30  to the sensor elements  18 ,  20  of the sensor holder  16 . 
     Sensor assembly  10  may be comprised of thermoplastic materials, thermoelastic materials, silicone rubbers, etc. Sensor assembly  10  may be comprised of a plurality of different materials having different material properties. For example, collar  12  may be of a stiffer material than the material of fenestrated region  14  and/or sensor holder  16 . One of ordinary skill in the art would appreciate a wide variety of different materials that may be utilized to practice the present invention. 
     Referring to  FIG. 11 , another embodiment of the sensor assembly  10  is illustrated. In this embodiment, collar  12  of sensor  10  is less massive than the embodiments of FIGS.  1 .- 10 . Collar  12  of  FIG. 11  may be comprised of a different material than other elements of sensor  10 . For example, collar  12  may have a different durometer than other portions of sensor  10 , but may otherwise be of an identical or similar material. As a result, collar  12  of the present invention need not be thicker than other portions of sensor  10 . Collar  12  is defined as the structure proximate the digit opening of sensor  10 . 
     In application, the digit is inserted into sensor assembly  10  and the lead wire  22  extends from the sensor assembly  10  and is connected to a physiological monitor. The sensor assembly  10  is maintained in place by resilient forces created by the collar  12 , fenestrated region  14  and sensor holder  16 . The strain relief  30  and collar  12  cooperate to oppose lateral movement of lead wire  22 . Preferably, the fenestrated region  14  has a reduced capability to transfer forces applied at the collar to the sensor holder  16 . In one embodiment of the present invention, the fenestrated region would be minimally capable of transferring a compressive force from the collar  12  to sensor holder  16 , and would instead buckle or deform under such a compressive force. In a preferred embodiment, the strain relief  30  positions the lead wire  22  away from the center of the inserted finger. With this offset of lead wire  22  relative to the longitudinal axis of the sensor assembly  10 , the patient is able to curl his finger without tensioning the lead wire  22  and disturbing the sensor holder  16 . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, device, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.