Abstract:
A medical device, such as an electrocardiogram (ECG) monitoring apparatus, provides galvanic isolation between low voltage electronics and a plurality of externally exposed ECG (patient contact) lead wires and electrodes. The ECG lead wires and/or electrodes can potentially make unwanted contact with sources of high voltage, such as from defibrillation pulses generated by defibrillation devices. The defibrillation pulses can cause damage to the low voltage electronics within the ECG monitoring apparatus. Electrical resistance is provided outside of the ECG lead wires and electrodes and separate from the low voltage electronics to protect against misdirection of a defibrillation pulse towards the low voltage electronics, and to protect against misdirection of a defibrillation pulse away from the patient for which the benefit of the defibrillation pulse is intended.

Description:
CROSS-REFERENCE TO APPLICATIONS INCLUDING RELATED SUBJECT MATTER 
   This application includes subject matter that is related to subject matter included within U.S. design Pat. application Serial No. 29/217,149, filed Nov. 12, 2004. 
   FIELD OF THE INVENTION 
   This invention relates generally to an apparatus that is configured to provide galvanic isolation between low voltage electronics and a plurality of externally exposed lead wires and electrodes that can potentially make contact with sources of high voltage, and in particular to a medical apparatus, such as an electrocardiogram (ECG) monitoring apparatus, that is configured to provide galvanic isolation between low voltage electronics and a plurality of externally exposed lead wires and electrodes that can potentially make contact with sources of high voltage, such as defibrillation pulses. 
   BACKGROUND OF THE INVENTION 
   Medical devices are typically operated inside of a health care environment in close proximity to patients, other electrical devices and other objects made of conductive material. As a result, there is a risk of unwanted transfer of electrical energy between such devices and such objects while providing health care to a patient. 
   For example, an electrocardiogram (ECG) monitoring apparatus is a medical device that receives and processes electrocardiogram (ECG) signals generated by a circulatory system of a person. The apparatus typically includes a plurality of ECG (patient contact) electrodes that are each electrically connected to a lead wire and that are each configured to make physical contact with the person being monitored. The ECG electrodes and lead wires are also configured to receive and relay ECG signals generated by the person to components of the ECG monitoring apparatus that process the ECG signals. 
   In some circumstances, the person may be experiencing some sort of cardiovascular instability, such as ventricular fibrillation. Ventricular fibrillation is a disturbance of electrical activity within a ventricular muscle of the heart. In order to arrest ventricular fibrillation, the patient may be administered a defibrillation shock via defibrillating device. In some circumstances, the patient may be administered the defibrillation shock while the patient is being monitored by an ECG monitoring apparatus. The defibrillation shock can create a voltage surge that can unintentionally conduct (travel) through one or more of the ECG contact electrodes and/or lead wires and can cause damage to the components of the ECG monitoring apparatus that process those ECG signals. 
   SUMMARY OF THE INVENTION 
   The invention provides for a method and apparatus for providing galvanic isolation between a medical device and other sources of electrical energy within a health care environment. In one embodiment, the invention provides for an electrocardiogram (ECG) monitoring apparatus and method that provides improved galvanic isolation between low voltage electronics that process ECG signals and a plurality of externally exposed ECG (patient contact) electrodes and lead wires that receive and relay the ECG signals to the low voltage electronics. 
   An electrical resistance is provided that corresponds to each of a plurality of external and detachable ECG (patient contact) lead wires and electrodes. Each ECG (patient contact) lead wire is configured to electrically connect to and include an ECG (patient contact) electrode. Each ECG (patient contact) electrode is configured to attach to a patient. 
   In accordance with the invention, the electrical resistance is provided outside of the ECG lead wires and electrodes and separate from the low voltage electronics. The electrical resistance is preferably implemented as a galvanically shielded resistor that is located in series between the low voltage electronics and a corresponding ECG lead wire. The electrical resistance protects the low voltage electronics against the occurrence of a high voltage surge (defibrillation pulse), conducted through an ECG (patient contact) electrode and or lead wire. Also, the electrical resistance protects against misdirection of a defibrillation pulse away from the patient for which the benefit of the defibrillation pulse is intended. 
   Preferably, each ECG (patient contact) lead wire is electrically connected in series with the galvanically shielded resistor. In this type of embodiment, each ECG (patient contact) lead wire and/or electrode is simpler and less expensive to manufacture. Failure of a (patient contact) lead wire and/or electrode does not require repair or replacement of a corresponding resistor and failure of a resistor does not require repair or replacement of a corresponding ECG contact electrode and/or lead wire. 
   Optionally, a cavity encloses and provides mechanical support to the resistor and is dimensioned to accommodate a variety of resistor sizes. As a result, the manufacture of the ECG monitoring apparatus is flexible with respect to the selection and incorporation of a particular resistor among various types and sources of resistors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the invention can be better understood with reference to the claims and drawings described below. The drawings are not necessarily to scale, and emphasis is instead generally being placed upon illustrating the principles of the invention. In the drawings, like reference numbers are used to indicate like parts throughout the various views. Differences between like parts may cause those parts to be indicated by different reference numbers. Unlike parts are indicated by different reference numbers. 
       FIG. 1A  is a top view of an embodiment of an ECG monitoring apparatus including ten patient contact lead wires and electrodes that are configured to attach to a patient. 
       FIG. 1B  is a frontal view of the ECG monitoring apparatus of  FIG. 1A . 
       FIG. 2  illustrates a side cross-sectional view of a conductive pathway within a passageway of the ECG monitoring apparatus of  FIGS. 1A-1B . 
       FIG. 3A  is top perspective view of a lower carrier of  FIG. 2  with reference numbers identifying portions of passageways. 
       FIG. 3B  is top perspective view of the lower carrier of  FIG. 2  with reference numbers identifying portions of baffles. 
       FIG. 3C  is top perspective view of an upper carrier of the ECG monitoring apparatus of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A  is a top conceptual view of an embodiment of an ECG monitoring apparatus  120  including (10) ECG patient contact lead wires  122   a - 122   j  that include patient contact electrodes  210   a - 210   j  and that are configured to be attached to a person, also referred to as a patient. When the ECG lead wires  122   a - 122   j  are attached to the patient, the ECG signals generated by the patient (not shown) are received by the patient contact lead wires  122   a - 122   j  and processed by the ECG monitoring apparatus  120 . The (8) ECG lead wires  122   a - 122   h  are configured to make contact with the upper body (chest and arms) of the patient. The (2) lead wires  122   i - 122   j  are configured to make contact with the lower body (legs) of the patient. 
   In some circumstances, the patient may be administered a defibrillation shock (voltage surge), of typically about 2000 volts while being monitored by the ECG monitoring apparatus  120 . In some circumstances, a defibrillation shock can arrest instabilities of cardio activity occurring within the patient. 
   In this type of circumstance, a voltage surge associated with the defibrillation shock can unintentionally conduct (travel) through one or more of the patient contact lead wires  122   a - 122   j  and cause damage to low voltage electrical circuits located within the ECG monitoring apparatus  120  (See  FIG. 2 ). The voltage surge (energy) associated with the defibrillation shock is intended to be directed towards the patient in order to provide therapy to the patient. Objects that are in contact with or proximate to the patient can potentially cause the voltage surge (energy) of the defibrillation shock to conduct away from the patient, and cause the patient to be denied the benefit of the intended therapy. Consequently, a defibrillation voltage surge should not be allowed to travel away from the patient and towards the electronic circuitry of the ECG monitoring device  120 . 
   To function properly, portions of electronic circuitry residing within the ECG monitoring apparatus  120  that are vulnerable to a voltage surge should be protected from the detrimental effects of a voltage surge. Accordingly, embodiments of the invention provide for galvanic isolation of vulnerable portions of electronic circuitry residing within the ECG monitoring apparatus  120 . 
     FIG. 1B  is a frontal view of an outer surface  140  the ECG monitoring apparatus  120  of  FIG. 1A . As shown, a frontal side of the ECG monitoring apparatus  120  includes a lower row of (8) openings  136   a - 136   h  of passageways  236   a - 236   h  (See  FIGS. 2 ,  3 A) and an upper row of (2) openings  136   k - 361   l  of passageways  236   k - 236   l  (See  FIGS. 2 ,  3 B). The lower row of openings  136   a - 136   h  are configured to receive ECG patient contact lead wires  122   a - 122   h . The upper row of openings  136   k - 136   l  are configured to receive audio sensor cables (not shown). A rear side (not shown) of the ECG monitoring apparatus  120  includes (2) openings (not shown) of passageways receiving ECG patient contact lead wires  122   i - 122   j.    
     FIG. 2  illustrates a side cross-sectional view  200  of a passageway  236  within the ECG monitoring apparatus of  FIGS. 1A-1B . The passageway  236  includes a rear conductive (electronics side) pathway  126  that includes electrical components that are electrically connected in series. A front conductive (patient side) pathway  122 , shown as located outside of the apparatus  120 , also includes electrical components that are electrically connected in series. The front conductive (patient side) pathway  122  is attachable to and detachable from the rear conductive (electronics side) pathway  126 . A combined conductive pathway  130  represents the combination of the front conductive pathway  122  and the rear conductive pathway  126  when electrically attached to each other. As shown, the front conductive (patient side) pathway  122  is detached from the rear conductive (electronics side) pathway  126 . 
   The front conductive (patient side) pathway  122 , representing an individually detachable and replaceable ECG (patient contact) lead wire  122 , includes at a first end  121  and a second end  123 , an ECG (patient contact) electrode  210 , an insulated conductor  212  and an electrical connector  214 . The patient contact electrode  210  is located at the first end  121  of the front conductive pathway  122  and is electrically connected to an insulated conductor  212 . The insulated conductor  212  is also electrically connected to a female type of electrical connector  214  that is located at the second end  123  of the front conductive pathway  122 . A female type of electrical connector is less likely to make unwanted electrical contact with outside voltage sources. 
   The rear conductive (electronics side) pathway  126  includes a first end  125  and a second end  127 , a contact pin  224 , a base  222 , a resistor  220  and a conductor  218 . The contact pin  224  is located at the first end  125  of the rear conductive pathway  126  and is recessed within the passageway  236  in order to avoid accidental electrical contact with anything other than a patient contact lead wire  122 . 
   The contact pin  224  is also configured to make electrical contact with a resistor  220 . The resistor  220  is configured to make electrical contact with a conductor  218  that is configured to make electrical contact with a printed circuit board (PCB)  230  at the second end  127  of the rear conductive pathway  126 . The contact pin  224  is configured to physically and electrically engage the connector  214  in order to electrically attach the front conductive pathway  122  to the rear conductive pathway  126 . 
   The printed circuit board (PCB)  230  includes low voltage electronic components that can be damaged as a result of receiving a voltage surge traveling through the combined conductive pathway  130 . The resistor  220  is located in series between the first end  125  and the second end  127  of the rear conductive pathway  126  and is configured to provide substantial electrical protection to the PCB  230  from such a voltage surge. The resistor  220  is configured to reduce a voltage at locations between the resistor  220  and the second end  127  of the rear conductive pathway  126  relative to a voltage located at the first end  125  of the rear conductive pathway  126 . Preferably, the resistor provides 10 kilo-ohms of electrical resistance. 
   The resistor  220  delimits the rear conductive (electronics side) pathway  126  into a higher voltage portion and a lower voltage portion. The higher voltage portion includes the contact pin  224 , the base  222  and the resistor  220 . A lower voltage portion of the rear conductive pathway  126  includes the conductor  218  that is located downstream of the voltage reducing resistor  220 . 
   A lower carrier  226   a  and an upper carrier  226   b  are internal structures  226   a - 226   b  that bound the passageway  236  that substantially surround at least the higher voltage portion of the rear conductive pathway  126 . Preferably, the carriers  226   a - 226   b  also substantially surround the electrical connector  214  of the front conductive (patient side) pathway  122 , as shown. 
   The carriers  226   a - 226   b , as internal structures  226   a - 226   b  of the ECG monitoring apparatus  120 , are configured to provide mechanical support and electrical (galvanic) isolation to at least the higher voltage portion of the rear conductive (electronics side) pathway  126 . Encapsulating the higher voltage portion, such as the contact pin  224 , within the passageway  236 , helps prevent accidental contact between the contact pin  224  and an outside object of higher electrical potential. 
   A vertical baffle (not shown in  FIG. 2 ) forms a portion of an inner surface of the passageway  236  and is located in opposite horizontal directions (each side), as opposed to opposite vertical directions (above and below), the rear conductive pathway  126  (See  FIG. 3A ). The vertical baffle is formed from abutting (stacking) the lower carrier  226   a  and the upper carrier  226   b  together (Shown in  FIG. 2B ). Each vertical baffle provides additional galvanic isolation between high voltage potions of adjacent pathways  236 . 
   In accordance with the invention, notice that the front conductive (patient side) pathway (ECG patient contact lead wire)  122  excludes a resistor. As a result, the front conductive pathway (ECG patient contact lead wire)  122  includes less components and is easier and less expensive to manufacture than an ECG lead wire that includes a resistor. 
   Further, a failure of the resistor  220  located within the combined conductive pathway  130  does not require repair or replacement of a corresponding ECG (patient contact) lead wire  122 . Likewise, failure of an ECG lead wire  122  does not require replacement of a resistor  220  within the conductive pathway  130  within which the resistor  220  is located. Essentially, the resistor  220  is salvageable if the corresponding ECG lead wire  122  fails and the ECG lead wire is salvageable if the corresponding resistor  220  fails. 
   In accordance with the invention, neither is a resistor located within or near the low voltage electronics. Each high voltage portion of a conductive pathway  130  is required to be located a minimum distance from other high voltage portions of other conductive pathways  130 . For example, some printed circuit board (PCB) designs require high voltage connections from ECG lead wires to be at least 8 millimeters apart. Hence, accommodating (10) resistors that are each located within a high voltage portion of a pathway  130  can require occupation of a substantial portion of space provided by a circuit board  230  including the low voltage electronics. 
   Instead, in accordance with the invention, a resistor  220  is located (electrically connected) within the rear conductive pathway  126  and also located substantially away from the circuit board  230  and other low voltage electronics. Preferably, the resistor  220  is physically located within a cavity  232  that resides as a portion of the passageway  236 . The cavity  232  is also referred to as a barrel recess  232 . Optionally, the cavity  232  is dimensioned to accommodate a variety of resistor sizes. As a result, manufacture of the ECG monitoring apparatus  120  is flexible with respect to the selection of a particular resistor among various types and sources of resistors. 
   For example, if a first resistor supplier becomes unavailable, or can no longer supply a sufficient number of resistors or is no longer a supplier of choice, a second resistor supplier can be chosen even if the physical dimensions of the resistor supplied by the second resistor supplier differ from the physical dimensions of the resistor supplied by the first resistor supplier. Further, incorporation of the second resistor into the apparatus  120  does not force changes to other components of the apparatus  120 . 
   The location of the resistor  220  within the rear conductive (electronics side) path  126  and not within the front conductive (patient side) path  122 , causes the higher voltage portion of the combined conductive pathway  130  to reside within the apparatus  120 . The lower  126   a  and upper carriers  126   b  provide galvanic isolation and mechanical support to the higher voltage portion of the combined conductive pathway  130 . 
     FIG. 3A  is top perspective view of the lower carrier  226   a  of  FIG. 2  with reference numbers identifying portions of passageways  236   a - 236   h  within the ECG monitoring apparatus  120  of  FIG. 2 . As shown, the lower carrier  226   a  is manufactured from injection molded plastic and includes indentations  236   a - 236   h  that each define a lower portion of each of the (8) lower front passageways  236   a - 236   h  and each of the (2) rear passageways  236   i - 236   j . The lower portion and an upper portion of each of the passageways  236   a - 236   j  are formed by stacking (abutting) the upper carrier  226   b  on top of the lower  226   a  carrier. The upper portion of each of the (10) passageways  236   a - 236   j  is included within the lower surface of the upper carrier  226   b  (See  FIG. 3C ). 
   As shown, passageways  236   c  and  236   d  each include electrical components that are connected to form rear conductive pathways  126   c  and  126   d  respectively as also shown in  FIG. 2 . Each of the conductive pathways  126   c - 126   d  are constructed from the connection of a contact pin  224 , a base  222 , a resistor  220  and a conductor  218  as described in association with  FIG. 2 . Preferably, other rear conductive pathways  126 , like that described in association with  FIG. 2 , are included within all of the passageways  236   a - 236   j.    
     FIG. 3B  is top perspective view of the lower carrier  226   a  of  FIG. 2  with reference numbers identifying portions of (5) baffles  238   a - 238   e . As shown, the lower carrier  226   a  also includes a lower portion of each of (5) baffles  238   a - 238   e  in addition to the lower portion of each of the (10) passageways  236   a - 236   j . The baffles  238   a - 238   e  are each located in between adjacent pairs of front lower passageways  236   b - 236   g . The baffles  238   a - 238   e  are configured to provide additional galvanic isolation between pairs of adjacent passageways  236   b - 236   g  that are located at distances closer to each other than distances between pairs of other passageways including  236   a ,  236   h ,  236   i - 236   j . The passageways  236   a ,  236   h ,  236   i - 236   j  are cylinder shaped and do not require a baffle. 
   Each of the (4) lower front passageways  236   c - 236   f  are disposed between two of the (5) baffles  238   a - 238   e . For example, passageway  236   c  is disposed between baffles  238   a  and  238   b  and passageway  236   d  is disposed between  238   b  and  238   c  and passageway  236   f  is disposed between  238   d  and  238   e . An upper portion of each of the (10) front and rear passageways  236   a - 236   j  and an upper portion of each of the (5) baffles  238   a - 238   e  is provided by the lower surface of the upper carrier  226   b  (See  FIG. 3C ). 
     FIG. 3C  is top perspective view of an upper carrier  226   b  of the ECG monitoring apparatus  120  of  FIG. 2 . As shown in this embodiment, the upper carrier  226   b  is manufactured from injection molded plastic and is configured (shaped) to stack (abut) on top of the lower carrier  226   a . The bottom side (not shown) of the upper carrier  226   b  includes an upper portion of each of the (8) lower front passageways  236   a - 236   h  and an upper portion of each of the (2) rear passageways  236   i - 236   j , an upper portion of each of (5) front baffles  238   a - 238   e . The top side of the upper carrier  226   b  includes the additional (2) upper front passageways  236   k - 236   l  which are bounded from above by the outer surface  140  of the apparatus  120  (See  FIG. 1B ). Each of the additional (2) upper front passageways  236   k - 236   l  provide passage for audio cables (not shown). 
   When stacked on top of the lower carrier  226   a , the upper carrier  226   b  completes the formation of the lower front (8) passageways  236   a - 236   h , the formation of the (2) rear passageways  236   i - 236   j  and the formation of the (5) front baffles  238   a - 238   e.    
   The invention can be applied to various types of devices that include low voltage electronics and that can be damaged from outside electrical sources. This is particularly applicable to low voltage electronics having an electrical connection to a conductive path that can make unwanted contact with outside sources of electrical energy. 
   For example, medical devices that are configured to receive signals from wire connected pressure and/or thermal transducers, can be vulnerable from voltage surges from outside electrical sources. Also for example, other devices monitoring EKG signals (brainwaves), cardiac output, blood pressure or other physiological data from a patient can be vulnerable to unwanted contact and damage from electrical sources of high voltage. 
   Besides a defibrillator, there are many other electrical sources of voltage within proximity to a patient within a health care environment that can potentially create a high voltage contact with devices that include low voltage electronics. For example, electrical cutting tools used for surgery on a patient, or electrical thermal devices that apply heat to a patient, are likely sources of high voltage. Operation of these types of tools may cause an unwanted transfer of electrical energy to other devices that include low voltage electronics and that are located in proximity to a patient. Devices that simply draw line voltage from a standard electrical outlet, such as a lamp, can possible cause unwanted transfer of electrical energy to other devices that include low voltage electronics and that are located in proximity to a patient. 
   While the present invention has been explained with reference to the structure disclosed herein, it is not confined to the details set forth and this invention is intended to cover any modifications and changes as may come within the scope and spirit of the following claims.