the following discussion is presented to enable a person skilled in the art to make and use the invention . various modifications to the preferred embodiment will be readily apparent to those skilled in the art , and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims . thus , the present invention is not intended to be limited to the embodiment show , but is to be accorded the widest scope consistent with the principles and features disclosed herein . fig1 illustrates a removable monitoring adapter system 10 . the adapter features a set of monitoring electrode connectors 12 . the configuration shown in fig1 shows three monitoring electrode connectors ra , ll and rl typical of the configuration used in connection with a right leg drive monitoring configuration . each of the three electrode connectors 12 are connected to an adapter 16 via connection wires 14 . as will be appreciated by persons of skill in the art , the connection wires may associate with the adapter 16 separately ( as shown ) or may be configured such that they form a single wiring bundle . disposable monitoring electrodes ( not shown ) are connected to the electrode connectors 12 . disposable monitoring electrodes could be attached , for example , by means of a snap connector or a clamp . suitable electrodes include , for example , 3m red dot monitoring electrodes . additional , other connection means may also be provided without departing from the scope of the invention . as will be appreciated by those of skill in the art , monitoring electrode pads could also be formed integral with the adapter system 10 . however , in such an instance the cost benefit associated with using disposable electrodes may be subverted if the integrated monitoring electrodes are not reusable . additionally , the adapter system 10 may be configured to have more or fewer electrodes . typically , the adapter would be configured to have between 2 - 12 electrode connectors . the adapter 16 contains circuitry , discussed in more detail below , that enables the defibrillator to identify the presence of the adapter , thus configuring the defibrillator to monitor ecg and prohibit delivery of a defibrillation shock . in this embodiment , adapter 16 is connected to a connector 20 via a wire 18 . connector 20 provides a standard two wire connection to the defibrillator . although the adapter 16 and the connector 20 are shown in fig1 as being separated by wire 18 , it will be appreciated by those of skill in the art that the functionality of adapter 16 could be incorporated into connector 20 , thereby eliminating wire 18 without departing from the scope of the invention . additionally , the adapter 16 could be a removable reusable adapter . in that instance , the monitoring electrodes 12 would plug into the adapter 16 and the adapter 16 would , in turn , plug into the defibrillator . turning to fig2 a high level block diagram is depicted that illustrates the defibrillator 30 connected to monitoring electrodes 12 via a connector 20 and monitoring adapter 16 . although depicted as separate blocks , as discussed above , connector 20 and monitoring adapter 16 may be formed integrally as mentioned above . the major components of an aed 100 suitable for use in conjunction with this invention are shown in fig3 in block diagram form . in this example , aed 100 control functions are divided among a microprocessor unit ( mpu ) 102 and two custom gate arrays 104 and 106 . it should be understood , however , that gate arrays 104 and 106 are optional , and their functions can be performed by other circuits . mpu 102 performs program steps according to software instructions provided to it from rom 114 . mpu 102 controls the operation of certain buttons ( such as display contrast buttons 108 ) and certain system led &# 39 ; s 110 ( such as led &# 39 ; s associated with the shock button and the electrode connector ). mpu 102 receives system status information as shown by block 112 . mpu 102 also controls the operation of the display contrast button 108 . as shown in fig3 gate array 104 implements a memory map to system rom 114 , data card port 116 and other system memory elements . gate array 106 provides a system monitor function by initiating automatic self - tests of the defibrillator and its components . the gate array 106 displays the operational status of the defibrillator on a status display 128 . gate array 106 is also the defibrillator &# 39 ; s interface with a user - activated on / off switch 130 . gate array 106 also may control the power management subsystem 132 to provide power to operate system components from battery 134 and to provide energy to the shock delivery system &# 39 ; s capacitor ( s ) for a therapeutic shock during treatment mode . power management subsystem 132 enables energy from the battery 134 to be delivered to the patient 18 via shock delivery and ecg front end 124 . for that purpose , power management subsystem 132 includes a capacitor ( not shown ). gate array 106 also interfaces with the defibrillator &# 39 ; s ecg front end 124 , providing data to the mpu , which performs detection of a patient ecg pattern requiring treatment . the gate array 106 also controls delivery of the shock to electrode connector 136 , upon actuation of the shock button , in response to shock delivery status information obtained during delivery of the shock . the front end 124 provides for an impedance measurement to be made by mpu 102 , via connector 136 . for example , a preliminary fixed current waveform is delivered to the connector 136 . a suitable signal would be , for example , a 540 hz signal . a return signal is received by the defibrillator front end 124 , and delivered to mpu 102 , which calculates the impedance present at connector 136 . by analyzing the impedance , mpu 102 can determine if the monitoring adapter is present at connector 136 , and select software instructions from rom 114 which configures the defibrillator as a monitor only , thus suppressing the defibrillation function . when mpu 102 determines that the adapter is present , mpu 102 can also determine if monitoring electrodes are disconnected from the patient . if the impedance analysis determines that the monitor adapter 16 is not present , then the standard software instructions are selected and the aed functions normally . further information regarding defibrillator operation be found in u . s . pat . no . 5 , 735 , 879 by gliner et al . for “ electrotherapy method for external defibrillators ” and u . s . pat . no . 5 , 607 , 454 by cameron et al . for “ electrotherapy method and apparatus ,” the disclosures of which are incorporated herein by reference . as is known in the art , the aed 100 can be operated in different modes , such as self - test mode , stand - by mode and patient treatment mode . further discussion of the operation of an external defibrillator in self - test mode , stand by mode and patient treatment mode is provided in u . s . pat . no . 5 , 800 , 460 by powers et al . for “ method for performing self - test in a defibrillator ”, the specification of which is incorporated herein . fig4 illustrates a circuit implementation of the monitor adapter , which includes a right leg drive system similar to that which is commonly known in the art . typically modern electrocardiographic systems do not ground the patient . in order to overcome the interference effects of large common mode signals present on an un - grounded patient the right - leg electrode is connected to the output of an auxiliary op amp 200 , which effectively shunts the common mode currents away from sense electrodes ra and ll . the common - mode voltage on the body is derived by averaging the signals present at ra and ll , via the output of unity gain amplifiers 202 and 204 , with resistors r 1 and r 2 . this average is inverted , amplified and fed back to the right leg , rl , via the output of the auxiliary op amp 200 through resistor r rl . bias voltage of 1 . 18 v is also established for amplifiers 202 and 204 via this feedback path . the negative feedback then drives the common - mode voltage on the body to a low value , thus minimizing the interference in the patient &# 39 ; s ecg . resistor r rl is located in series between the patient and the op amp 200 which , in the event of an abnormally high voltage , would limit the current to a safe level . op amps 202 and 204 buffer the ecg signal received via ra and ll , providing a low impedance unity gain ecg signal for the aed at v 1 and v 2 . input resistors r ra and r ll and diodes ( d 1 , d 2 , d 3 and d 4 ) protect op amps 202 and 204 against high voltage transients that might be present , such as the presence of another defibrillator . capacitors c 1 and c 3 provide high - frequency filtering of the input signal received from ra and ll . resistors r 3 and r 7 provide a bias current which will drive the amplifier outputs of op amps 202 and 204 to ground if an electrode is removed from the patient . inductor 210 , resistor r 5 , capacitor 230 , and switch 250 , present a unique impedance interface 215 at v 1 , v 2 , which enables the aed to detect the presence of the monitor adapter , as well as disconnected electrodes ra , rl , or ll . interface 215 presents significant inductive reactance and resistance to the aed . when the aed is connected to a patient using defibrillation electrode pads , under normal conditions , the patient impedance presents a distinctly different impedance , including capacitive reactance and much lower resistance , than the monitor adapter . thus , the aed can be configured to operate in either normal defibrillation mode or monitor mode only , depending on the impedance measured at the patient connector . in a preferred embodiment the inductor 210 is 470 mh , capacitor 230 is 0 . 12 μf , and resistor r 5 is 3 . 4 kω . when the monitor adapter is connected to the aed then the following impedance relationships measured by the aed shall hold ( where a small - signal 540 hz impedance data is analyzed to indicate the device ): when the adapter is present and the leads are connected to the patient , then switch 250 disconnects capacitor 230 from the interface and the aed measures a 3 . 4 kω resistor in series with inductor 210 , thus meeting the impedance requirements for an adapter connected with all leads on the patient . the j - fet switch 250 in series with a capacitor 230 together function as an electrode disconnect and battery fault encoder for the monitor impedance . in the event a lead is off , or a battery fault condition occurs , j - fet 250 is switched to a low resistance state , thus connecting capacitor 230 in parallel with inductor 210 . the capacitor 230 causes the inductive reactance to increase as seen by the defibrillator , thus meeting the impedance requirements for an adapter with one or more leads off . comparator 220 and op amp 228 form the logic and control for switch 250 , which enables the leads off and battery fault function . if the battery is low , or any of the leads are disconnected , then comparator 220 drives the inverting input of op amp 228 high , thus driving the gate of j - fet switch 250 low , which in turn causes low switch resistance . logic 220 includes voltage comparators 222 a and 222 b and zener diode 224 . zener diode 224 sets the reference voltage for the system . in fig5 defibrillator measures the complex impedance at the patient connector by delivering a current signal to the connector and measuring the resulting voltage signal . when the defibrillator is directly connected to a patient , the impedance measured by the defibrillator meets the normal resistive operating requirements , and the defibrillator functions normally . in contrast , when the defibrillator is used in conjunction with the adapter 16 ( connected in series with monitoring electrodes 12 or integral with the monitoring electrodes , as shown in fig1 ), the impedance signal measured by defibrillator meets the monitoring adapter detection requirements , which include inductive reactance , z i , and high resistance , z r . thus the defibrillator is reconfigured as a passive monitor suppressing the shock capability of the defibrillator . turning to the specifics of fig5 which describes a method for using the adapter in conjunction with an aed . the first step is to turn the aed on 300 . next , a complex impedance is measured , for example , at the patient connector 302 . if z i / z r is greater than threshold 1 304 then the monitoring mode is enabled 308 . if z i / z r is less than or equal to threshold 1 304 then the monitoring mode is not enabled 306 . once monitoring mode is enabled , it is determined whether z i , is greater than threshold 2 310 . if z i , is greater than threshold 2 then a fault or fault condition 312 exists . if z i is not greater than threshold 2 , then no fault or fault condition exists . examples of values for z i is provided in more detail above . modifications to the invention embodiments described above will be apparent to those skilled in the art . such modifications are within the scope the invention .
a defibrillator system capable of defibrillation and patient monitoring . when used as a patient monitor , the defibrillator system includes a defibrillator and removable monitoring electrodes . the monitoring electrodes communicate with a monitoring adapter and the defibrillator . a method of detecting the presence of the monitoring electrodes by the defibrillator is also included . a removable monitoring adapter . the removable monitoring adapter having a test impedance . defibrillators include semi - automatic defibrillators and automatic defibrillators .