Abstract:
A sensor for use with a polysomnograph in a sleep lab setting is made reusable by laminating a PVDF film and associated lead contacts within a flexible, moisture-impervious plastic envelope that is hermetically sealed about its periphery. Lead terminals within the envelope are adhered to the metalized surfaces of the PVDP film using a conductive adhesive which inhibits dislodgement of the leads from the sensor even with rough handling and cleaning.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Provisional Application Ser. No. 60/700,365, filed Jul. 18, 2005, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to apparatus for monitoring respiratory activity, which also can include snoring activity, and more particularly to a reusable pyro/piezo transducer for producing an electrical signal proportional to respiratory airflow and/or vibration due to snoring episodes for subjects undergoing sleep studies. 
     2. Discussion of the Prior Art 
     Applicant&#39;s assignee, Dymedix Corporation of Minneapolis, Minn., has pioneered the development of improved sensors that are adapted to be attached to the upper lip or throat area of a patient that, during sleep, produces an electrical signal proportional to inspiratory and expiratory airflow and to episodes of snoring. In U.S. Pat. No. 5,311,875, applicant first disclosed such a sensor embodying a polyvinylidene fluoride (PVDF) film as the active element of such a respiration activity sensor. The film has both pyroelectric and piezoelectric properties and, as such, is responsive to both temperature changes and physical vibration, producing an electrical signal output that can be signal processed to effectively separate the temperature change induced signal from the signal due to vibration. 
     Improvements in the sensor are the subject of U.S. Pat. Nos. 6,894,427, 6,551,256, 6,485,432, 6,491,642 and 6,254,545, the teachings of which are hereby incorporated by reference as if set forth in full herein. 
     For the most part, the sensor construction described in the aforereferenced patents were intended for single-use application in that they would not hold up to repeated cleaning. More particularly, moisture could permeate the layered construction to compromise the electrical interface between the PVDF film and its connection to an electrical lead. Moreover, the handling during cleaning operations would lead to detachment of the lead&#39;s contact with the PVDF film. 
     It is accordingly a principal object of the present invention to provide a respiratory activity sensor especially constructed so as to be reusable. More particularly, the sensor or transducer of the present invention is designed to be moisture impervious and constructed such that lead wire pull-out is no longer a problem. 
     SUMMARY OF THE INVENTION 
     In fabricating the sensor of the present invention, a sandwiched construction is employed in which a PVDF film is coated on its opposed major surfaces with a conductive layer and a pair of lead wires having a metal tab attached to the distal ends thereof are positioned on opposite sides of the PVDF film using a carbon-laced adhesive as a conductive bonding agent between the lead wire&#39;s metal tabs and the conductive coating on the PVDF film. 
     The PVDF film with the lead contact tabs affixed to its opposed major surfaces are sandwiched between upper and lower layers of double-sided adhesive tape that adhere to the film layer, to a portion of the leads and to one another. Next, a polyurethane film layer is adhered to the exposed sides of the double-sided tape. The polyurethane layers extend beyond the perimeter edges of the double-sided tape and the edge portions of the polyurethane layers are heat sealed to one another to totally encapsulate the PVDF film, the lead tabs and the layers of double-sided adhesive tape in a moisture-proof manner. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of the reusable sensor constructed in accordance with a first embodiment of the invention; 
         FIG. 2  is an expanded edge view of the embodiment of  FIG. 1 ; and 
         FIG. 3  is an exploded view of an alternative embodiment of a snore sensing element made in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the device and associated parts thereof. Said terminology will include the words above specifically mentioned, derivatives thereof and words of similar import. 
     Referring to  FIGS. 1 and 2 , there is shown an exploded perspective view and an exploded edge view of a reusable airflow sensor especially designed for use with a polysomnograph in a sleep lab setting. The sensor comprises as its active element a polarized PVDF film layer  10  that, in the embodiment of  FIG. 1 , is somewhat Y-shaped having rounded lobes  12 ,  14 , diverging from one another at a predetermined angle and a stem portion  16 . The PVDF film layer  10  includes metallization layers on opposed major surfaces thereof represented by the cross-hatching thereon. The metallization layers serve to collect the charge produced by the PVDF film due to respiratory air flow impinging on the transducer or due to temperature change. 
     Affixed to the opposed major surfaces of the stem portion  16  are conductive electrode tabs  18  and  20  that are crimped and/or soldered to the exposed ends of insulated lead wires  22  and  24 , respectively. To insure intimate contact between the conductive electrodes  18  and  20  and the metalized surfaces of the PVFD film  10 , a conductive adhesive, such as that sold under the trademark ARclad® by Adhesives Research, Inc., is used. This material comprises an adhesive that is laced with conductive carbon particles that serves as a bonding agent between the electrodes  18  and  20  with the metalized layers adhered to the PVDF film. The ARclad® adhesive is represented in  FIG. 1  by references numerals  26  and  28 . 
     Pyro/piezo transducers of the type described can be procured from Measurement Specialties, Inc. of Morristown, Pa., with leads already attached to the metalized PVDF film, but the film shape is of one type—rectangular—and of a standard size. 
     First and second double-sided adhesive tape layers  30  and  32  cut to conform to the shape of the PVDF layer  10  are adhered to the opposed surfaces of the film layer  10  helping to secure the tab electrodes  18  and  20  and a portion of the wire leads  22  and  24  leading to the conductive tabs in place. Completing the assembly are first and second layers  34  and  36  of polyurethane film that are also cut to be of generally the same shape as the PVDF layer  10 , but larger in size than the adhesive tape layers  30  and  32 . During assembly, the polyurethane plastic layer  34  is adhered to the exposed adhesive surface of the double-sided tape layer  30 . Likewise, the polyurethane plastic layer  36  is bonded to the exposed adhesive on the tape layer  32 . 
     Because the polyurethane plastic layers  34  and  36  are of a larger area than the tape layers  30  and  32 , a perimeter portion  38  extends beyond the edges of the tape layers  30  and  32 . The perimeter portions of the polyurethane layers  34  and  36  are brought into contact with one another and fused together in a thermal bonding process. As a result, the interior components sandwiched between the outer polyurethane plastic layers  34  and  36  are fully encapsulated and thereby sealed against ingress of moisture even when exposed to cleaning solutions and sterilants. Also, because of the manner in which the electrode tabs  18  and  20  are adhered to the PVDF layer  10  by the ARclad® conductive adhesive and the way in which the portion of the leads leading thereto are adhesively attached to the tape layers  30  and  32 , testing has shown that the wire leads  22  and  24  will break before the electrodes will pull free from the sensor assembly. 
     While polyurethane film is preferred for the outer layers  34  and  36 , because it is heat-sealable and hydrophobic, other non-porous heat sealable plastic materials may also be used to encapsulate the PVDF and the distal ends of the lead wires. 
     In use, the sensor of  FIG. 1  is placed on the upper lip of a subject such that the lobes  12  and  14  are proximate the nasal openings and the stem portion  16  extends beyond the upper lip. Sensor  10  is held in place on the lip by means of a suitable adhesive or by using a strip of adhesive tape. Changes in temperature due to inspiratory and expiratory airflow that impinges on the sensor produce an output signal component proportional to the temperature swings. Should there be episodes of snoring, the sensor that is in contact with the skin, will sense the snoring vibration and the piezoelectric properties of the PVDF will result in a second signal component that varies with the intensity of the snoring. These signals are fed to a polysomnograph instrument where signal processing circuitry is used to separate the pyro signal from the piezo signal. 
     Turning next to  FIG. 3 , there is shown an alternative embodiment especially designed for attachment to the throat area of a sleeping patient in a sleep lab environment. This sensor is also reusable in that it can be cleaned. It is substantially identical in its construction to the embodiment as illustrated in  FIGS. 1 and 2  and corresponding numbers, only primed, are applied to the embodiment of  FIG. 3 . The only difference between the embodiments of  FIG. 1  and  FIG. 3  is the shape of the sensor. In that the constructional details have already been explained in connection with the embodiment of  FIGS. 1 and 2 , it is felt unnecessary to repeat it in connection with the embodiment of  FIG. 3 . 
     This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.