CA1326884C - Cardiac probe enabling use of personal computer for monitoring heart activity or the like - Google Patents
Cardiac probe enabling use of personal computer for monitoring heart activity or the likeInfo
- Publication number
- CA1326884C CA1326884C CA000576941A CA576941A CA1326884C CA 1326884 C CA1326884 C CA 1326884C CA 000576941 A CA000576941 A CA 000576941A CA 576941 A CA576941 A CA 576941A CA 1326884 C CA1326884 C CA 1326884C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- probe
- computer
- output
- circuit means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/25—Bioelectric electrodes therefor
- A61B5/279—Bioelectric electrodes therefor specially adapted for particular uses
- A61B5/28—Bioelectric electrodes therefor specially adapted for particular uses for electrocardiography [ECG]
- A61B5/282—Holders for multiple electrodes
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/30—Input circuits therefor
- A61B5/301—Input circuits therefor providing electrical separation, e.g. by using isolating transformers or optocouplers
Abstract
Cardiac Probe Enabling Use of Personal Computer for Monitoring Heart Activity or the Like Abstract of the Disclosure A compact and economical probe unit has projecting electrodes for sensing minute voltage variations at spaced apart locations on a persons skin or other surface.
Internal circuits generate serial form digital signals indicative of the voltage variations for transmission to a personal computer where an electrocardiogram or other data presentation may be displayed. The probe includes a digital type of optical isolator through which the serial signals are transmitted, the output circuit of the isolator being energized by voltage taken from the computer and the input circuit being independently energized from a battery within the probe and thus there is no electrically conduct-ive path between the computer and the electrodes. Among other uses, the probe enables unskilled persons to monitor their own heart activity as it is economical, safe and easily operated and makes use of a common computer for display rather than a costly electrocardiograph.
Internal circuits generate serial form digital signals indicative of the voltage variations for transmission to a personal computer where an electrocardiogram or other data presentation may be displayed. The probe includes a digital type of optical isolator through which the serial signals are transmitted, the output circuit of the isolator being energized by voltage taken from the computer and the input circuit being independently energized from a battery within the probe and thus there is no electrically conduct-ive path between the computer and the electrodes. Among other uses, the probe enables unskilled persons to monitor their own heart activity as it is economical, safe and easily operated and makes use of a common computer for display rather than a costly electrocardiograph.
Description
2714.1 -1- 1 326884 Pat~nt Cardiac Probe Enablin~ Use of Personal Com~uter for Monitorinq Heart ActivitY or the Like Technical Fleld Thls invention relates to instruments for producing S electrocardiograms or the like and more particularly to a compact and economical probe which enables display of such qata at the screen of a personal computer.
8ackaround of the Invention Electrocardiographs which visually display the heart actlvlty of llving sub~ects are well recognized to be of great value in the diagnos~s and treatment of medical patients. Instruments of this type are also useful for a number of other purposes such as ln the monitoring of cardlac act~vity in persons undergoing exercise training or for the display of an ECG for educational purposes.
The conventional electrocardiograph i8 a complex, costly and usually bulky assembly which must be operated by professional medical personnel or highly skilled technicians. Conseguently, usage of such equipment has more or less been restricted to hospitals, medical clinics, and medicial emergency vehicles. Compact and economical cardlac monltors have been developed but in general these produce only an audible signal or otherwise do not provide the type of data that is available f rom an ECG.
A more compact and economical cardiac monitor would be 3~ ' ,.
.
. , , - . :: ~ , . : ' ,.. . . . .
: --- , - ~ . .
highly advantageous not only in medical facilities but also for usage elsewhere. Such a device would for example, enable persons with cardiovascular problems to monitor their heart activity in their homes. Such apparatus should not require that the operator have specialized skills or undergo extensive training and should not expose the user to potential hazards such as electrical shock.
Instruments for obtaining electrocardiograms include spaced apart electrodes which contact the persons skin in the thoracic region in order to sense the minute voltage changes which accompany heart activity. The sensed voltage changes are amplified and displayed on the screen of an oscilloscope and/or are applied to a chart recorder or printer type of readout device to provide the electrocardiogram. The sensed voltage signals have also heretofore been digitized and transmitted to a computer which may variously be programmed to detect abnormal activity, to determine average values for specific phases of the cyclic heart activity or to analyze the data in a variety of other ways.
Prior computer aided heart monitoring systems do not resolve the problems discussed above. The computer typically functions only as a permanent component of the electrocardiograph and is not used for any other purpose.
Thus it further increases the cost and often the bulk of the heart activity monitoring installation. The prior computer aided systems, like older types of electrocardiograph/ require highly trained operators.
The present invention is directed to overcoming one or more of the problems discussed above.
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Summarv of the Invention In accordance with one aspect of the invention there is provided a unitary probe for producing and transmitting computer compatible serial form digital signals indicative of heart activity of a subject to a spaced apart digital computer of the general purpose type at which software may be changed by the operator to run any of a variety of different computer programs and which has a serial data input port, comprising: a probe housing having a configuration adapted for disposition at the thoracic region of said subject and having signal output means for transmitting said digital signals to said serial data input port of said computer; first, second and third electrodes secured to said housing and extending outward from a surface thereof, said electrodes being mutually spaced apart; first circuit means for producing a first analog signal which varies in accordance with variations of the electrical potential at said first electrode relative to the electrical potential at said third electrode: second circuit means for producing a second analog signal which varies in accordance with variations of the electrical potential at said second electrode relative to the electrical potential at said third electrode; third circuit means for producing a third analog signal which varies in accordance with variations of the difference between said first and second analog signals;
sign~l conversion circuit means for converting said third analog signal to sequences of serial form digital signal bits:
each of said circuit means being within said probe housing;
an electrical power supply disposed within said probe housing and being coupled to each of said circuit means to supply operating current thereto; and isolating means for transmitting said sequences of signal bits to said serial data input port of said computer through said output means of said probe housing and which converts said signal bits to non-electrical form and then back into electrical form to electrically isolate said subject from said computer.
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The invention provides a compact and economical instrument which enables minute voltage variations between spaced apart areas of a surface, such as the human skin, to be sensed and converted into serial form digital signals which may be applied to a personal computer to provide a visual display indicative of the voltage variations at the monitor screen of the computer. Among other uses, the invention enables unskilled persons to monitor their own heart activity away from medical facilities as the construction can be inexpensive, safe and easy to operate and connects to a commonly available display, a personal computer, rather than a specialized electrocardiograph.
, .
Brief Description of the Drawings FIG. 1 depicts a cardiac activity probe and an associated computer in accordance with a preferred embodiment of the invention.
FIG. 2 is an end view of the cardiac activity probe of FIG. 1 taken along line II-II thereof.
FIG. 3 is a schematic circuit diagram of electronic components of the probe of the preceding figures.
FIG. 4 is a detailed circuit diagram of the differential amplifier and band pass filter amplifier components of the probe which are shown in block form in FIG. 3.
; FIG. 5 is a detailed circuit diagram of the optical isolator and interface driver circuits shown in block form in FIG. 3.
:~ . .:
, FIGS. 6 through 11 described a detailed computer pro-gram for enabling computer graphic display of data produced by the probe of the preceding figures.
FIG. 12 describes another suitable computer program for displaying data transmitted to a computer by the probe.
FIG. 13 depicts a print out of an ECG from data produced by the probe.
, Detalled Descrlption of the Preferred Embodiment Referrlng inltially to FIGS. 1 and 2 of the drawings in con~unction, a cardiac probe unit 11 in accordance with this particular embodiment of the invention has a housing member 12 which includes a triangular plate portion 13 and thic~er housing 14 at one surface of the plate. The hous- -ing 14 contains electronic components which will herelnafter be descrlbed. Externally visible components of the housing 14 include a manually operable on-off switch 16, an openable battery compartment lid 17 and a signal output port 18.
Plate portlon 13 defines an isosceles triangle with a base 19 that 18 shorter than the sides 21. First, second and third electrodes, 22, 23 and 24 respectively, are sltuated at the ends of conductive support posts, 26, 27, and 28 respectively, which extend outward from the surface 29 of plate 13 that 18 opposite from houslng 14. First electrode 22 18 located at the apex of the trlangular plate 13 at ~hlch sldes 21 converge. Second electrode 23 is at the right hand slde of base ~9 when the probe 11 18 ln the operatlng orlentatlon shown ln the draw~ngs and third elec-trode 24 1~ at the left slde of the base.
In ~eeplng wlth the common termlnology ln the art, the flrst, second and th~rd electrodes 22, 23, 24 may be herelnafter referred to respectively as the right arm elec-trode, the left leg electrode and the right leg electrode.
Thls does not mean that the electrodes 22, 23, 24 contact those partlcular portions of the human body during use.
The trlangular plate 13 is proportioned to fit over the frontal thoraclal reglon of the human body with the right arm electrode 22 belng over the sternum 30, left leg elec-trode 23 belng over the lower ribs 31 at the left side of the body and rlght leg electrode being over the lower ribs at the right slde of the body.
Posltloning of the electrodes 22, 23, 24 over bony regions of the body allows flrmer pressure to be exerted and reduces artifact in the signals due to electrode .
-.. . ... ~ . .. ..
movement. Such placement also reduces signal degradation from non-cardial muscle actlvlty.
The spaclng of electrodes 22, 23, 24 from plate 13 by support posts 22, 23, 24 enables firm contact of the elec-trodes with the skln by accomodating to the convexity ofthe human chest. The trlangular configuration of the probe ll 18 particularly useful for women as it avoids the areas of the breasts.
Each electrode 22, 23, 24 preferably has a concave contact surface 32 and thus ls essentially cup shaped.
Pressure 18 then concentrated at a circle on the skin and this reduces electrical resistance and also reduces effects from body hair.
Referring now to FIG. 3, electronic components of the probe 11 include a first clrcuit stage 32 which is a low gain differential amplifler of the type havlng hlgh common mode re~ection. The first stage 32 has inputs 33 and 34 connected to the rlght arm electrode 22 and left leg electrode 23 respectively. The right leg electrode 24 in 20 effect const~tutes a chassis ground for the f~rst stage 32 and certain other components of the probe 11 as will here-inafter be described in more detail.
Fir~t Btage 32 produces a first analog signal indica-tive o~ voltage variations at right arm electrode 22 25 relatlve to the voltage at right leg electrode 24 and also produces a second analog slgnal indicative of voltage vari-atlons at left leg electrode 23 relative to the voltage at the right leg electrode and transmits a third analog signal lndicative of the difference between the first and second 30 analog signals to a second circuit stage 36. Sensing the voltage at electrodes 22 and 23 relative to the voltage at electrode 24 re~ects the effects of electrical artifacts, such as charges produced by nearby electrical equipment, which can appear on the body surface with a much larger 35 amplitude than ECG signals.
The second circuit stage 36 is a band pass amplifler which eliminates direct current and low frequency compon-ents of the thlrd analog signal to eliminate base line .. , ~ , . .. , . .......... , . , : .,, ........ ; . ~ -., , .
1 326~
drlft and whlch al80 ellmlnates high frequency components to further reduce electrlcal artifact such as resldual power line slgnals and signals generated by surface muscle activity. Stage 36 may typlcal ly be configured to transmit 5 only frequencies in the range from about 0.5 Hz to about 25 Hz. In this speclfic embodiment, the band pass amplifer 36 also æhifts the the signal amplitude from +/- one volt to 2.5 volts +/- one volt to accomodate to the input signal acceptance range of this particular third circuit stage 37.
The third circuit stage 37 is an analog to digital signal convertor which may be of known constructlon and receives the third analog signal from circuit stage 36.
The clock circuit 38 of this particular analog to digital convertor 37 causes sampling of the third analog signal at 15 a frequency of 250 Hz and transmits an eight bit digital output slgnal in parallel form at each such sampli,n,g.
The fourth circuit stage 39 is a parallel to serial digital slgnal convertor which may also be of known con-structlon. Convertor 39 converts the parallel elght blt 20 slgnals recelved slmultaneously on eight lnput lines 41 lnto sequent1al bit s~gnals whlch can be transmltted on a single output llne 42. The output slgnalllng rate in this partlcular embodlment is 9,600 bits per second.
Irhe serlal form signals from circuit stage 39 are 25 transmltted to the lnput circult 43 of an optical isolator or coupler 44 ~hich may also be of known internal cons-tructlon. ~he lnput clrcult 43 converts the serial slgnal blts from electrlcal to optical form and the output clrcu$t 46 of the isolator reconverts the optical slgnals back to 30 electrlcal signal bits. 'rhis electrical$y isolates the electrodes 22, 23, and 24 from the computer 47 to which the probe 11 i8 coupled thereby eliminating any risk of elec-trical shock as there is no electrically conductive path between such components.
Digitlzlng and serializing of the signals within the probe 11 prior to transmission of the signals through optical isolator 44 contributes substantially to the - : .
.
~- 1 326884 ob~ective of provldlng an inexpensive monltoring device.
Dlgltal optlcal lsolators 44 and partlcularly slngle channel lsolators are less costly than analog lsolators whlch must sensitlvely respond to slight differences in S signal voltage rather than to two distinctly different voltage levels as in the case of digital isolators.
The sequence of serlal slgnals from optical isolator 44 is transmltted to the output port 18 of probe unlt 11 through a computer lnterface drlver circult 48 within the the probe 11. Clrcuit 48 operates as an ampllfler and level shlfter which converts the signal voltages into the standardized range reguired for the serlal input ports 49 of personal computers 47.
A four conductor cable Sl provides for coupllng of the probe 11 output port 18 with the serial port 49 which is present on personal computers 47 for the purpose of-receiving digital eignals ln serial form from an external source. Cable Sl has a connector 52 at one end compatible ~ith the serial port 49 of the particular brand of computer 49 and ha~ a connector 53 at the other end that 18 engagable ~lth probe port 18 and which connects each of the standard ~our pins ~not shovn) o~ the computer serial port 49 with a ~eparate one of four contacts 54, 56, 57 and 58 of probe port 18. The probe port 18, mating connector 53 and cable Sl may, if de~ired, be of the low cost type u6ed for telephone recei~er installations as four conductors are used ln each case.
Cable Sl connects contacts 56 and 57 with the nreceive data~ and ~signal groundn pins, respectlvely of the computer serial port 49 and connects contacts 54 and 58 wlth the nterminal ready~ and ~transmit data" pins, respectively, of the computer port. Output signals from the interface dri~er 48 are transmitted to the computer 47 through contact 56 with contact 57 being the slgnal ground conductor.
It is a characterlstic of standard personal computer serlal ports 49 that a a D.C. voltage of +5 volts is .: , : ~ ~ . - ; .
, .
, - ~
- , . ~ : ~
-lo- 1 32~(8~
present on the "termlnal ready" pin durlng operation and a D.C. voltage o~ -5 volts i8 present at the "transmit data"
pin when lt 1~ not transmitting. These voltages are used to provide operatlng power for the interface driver 48 and output clrcult 46 of the optical isolator of the present ~nventlon by connecting the power terminals such circuits 48 and 46 across contacts 54 and 58.
The lnput clrcult 43 of optical isolator 44 and clrcult stages 36, 37, 38 and 39 are provided with an inde-pendent D.C. power source 59. In particular, the probe 11 includes a battery 61 connected to a voltage regulator 62 ln series wlth the probe on-off swltch 16. Regulato~ 62 has posltive and negative outputs B+ and B- whlch apply op-eratlng power, at constant voltages relative to the chassls ground deflned by right leg electrode 24, to clrcult stages 32 and 36. Only posltlve voltage from terminal B+ ~ 8 18 applled to stagee 37 and 39 and isolator lnput clrcuit 43 whlch do not require blpolar power ln thls embodlment.
Use of D.C. voltage derlved from the computer 47 for operating th~ lnter~ace drlver 48 and output clrcult 46 of optical. lsolator 43 while the other components of the probe 11 operate fro~ ~n lndependent self-contalned power 8upply 59 re6ults ln there belng no electrlcally conductive path between the co~puter 47 and the electrodes 22, 23, 24. ThUE;
the computer 47 18 not a source of possible electrlcal shock and cant transmlt signal artifact to the electrodes.
FIG. 4 deplcts ~ultable clrcuit detail for the first and second clrcult stageB 32 and 36. In particular, right leg electrode 22 and left leg electrode 23 are connected to the non-invertlng inputs of a first palr of ampllflers 63 and 64 resp~ctlvely whlch ampllfy the mlnute voltages that are sensed by the electrodes. The output of ampllfier 63 18 connected to the output of ampllfier 64 through three - serles connectod resistors 66, 67 and 68. The circuit ~unctlon 69 between resistors 66 and 67 18 connected to the inverting input of ampllfler 63 and the clrcuit junction 71 between resistors 67 and 68 connects to the inverting lnput ,: , ., - ;,., ,' , ' ; - ~ , . .
.
of amplifier 64.
The amplified voltage signals from amplifiers 63 and 64 are respectively applled to the inverting and non-in-verting lnputs of a dlfferentlal amplifier 73 through input re61stors 74 and 76 respectively. A feedbac~ resistance 77 is connected across the lnverting input and output of amp-lifier 73 and an ad~ustable resistance 78 is connected between the non-lnvertlng lnput and ground. Resistanc~ 78 may be ad~usted to compensate for offset in amplifier 73 and to nu~l any common mode output.
~ he flrst and second analog signal voltages produoed by ampllflers 63 and 64 are proportional to the voltages sensed by electrodes 22 and 23 respectively at any glven time. Differentlal ampllfier 73 produces a third analog ~ignal voltage ~hlch varles ln accordance wlth variatlons of the dlfference between the flrst and second analog signals.
~ he secona clrcuit stage 36 or band pass fllter amp-llfier may include another ampllfier 79 havlng a non-ln-verting lnput coupled to the output of the dlfferentlal ampllfler 73 through a capacltor 81 and which 18 also connected to ground through a reslstor 82. Capacltor 81 and resl~tor 82 form a hlgh pass fllter whlch blocks dlrect current and supresses low rrequency slgnal varlatlons.
Another reslstor 83 and capacltor 84 are connected ln parallel across the lnvertlng lnput and output of amplifler 79 and functlon as a hlgh pass fllter which eliminates hlgh ~requency artlfact from the slgnal. An additlonal reslstor 86 connected between the lnverting lnput and ground operates ln con~unctlon ~lth reslstor 83 to establish the galn of the ampllfler 79 to provlde a signal voltage range compatlble wlth the partlcular analog to dlgital convertor 37 to ~hlch the ampllfler 18 coupled. Reslstor 85 whlch connect~ the lnvertlng lnput to B- provides offset.
aeferrlng now to FIG. 5, the input circuit 43 of optlcal lsolator 44 has a llght emlttlng dlode 87 connected between the power source terminal B+ and ground in series with a resistor 88 and receives the serial form digital ,:
.
: .:
1 732b~8~
slgnals from parallel to serial signal convertor 39 at the circult ~unction bet~een the diode and re~istor. The output circult 46 of lsolator 44 lncludes a photosensltive transl6tor 89 of the type ~hich exhlblts a variable gain ln response to changes ln the llght output of dlode 87 produced by the lncoming signals.
The interface drlver 48 may have still another amplif-ier 91 which has an output connected to the receive data contact 56 of the pro~e output port 18. The positive and negatlve pover lnputs of amplifier 91 are respectively connected to the transmit data contact 58 and terminal ready contact 54 of the output port 18 to supply operating voltage derlved from the computer. A capacitor 92 ls con-nected across 57 and 58 and another capacitor 93 is con-nected across contacts 54 and 57 to provide energy storage for the relatlvely hlgh impedance power supply form"ed by ,transmlt data and data terminal ready pins of the computer port.
The photosenslt1ve translstor 89 of optlcal lsolator 44 18 connected acro~s contacts 57 and 58 ln serles wlth a flxed res1~tor 94. The non-lnvertlng lnput og amplifler 91 connect~ to the clrcult ,~unctlon 96 between reslstor 94 and photosensltlve transistor 89 and also connects to ground contact 57 through a palr of 6eries resi6tors 97 and 98.
The lnvertlng lnput o~ the amplifier 91 connects to the clrcult ,~unctlon 99 bet-reen resistors 97 and 98.
Ampli~ler 91 ln con~unction ~,rith resistors 97 and 98 act~ as a co~parator whlch converts the voltage varlations across photosen~ltlve transistor 89 to a voltage range that 30 is compatlble ~lth the computer, for example to +/- 5 ' ' volts ~or the EIA RS-232 format.
Re~err~ng agaln to FIG. 1, the signals transmitted to computer 47 ~ay var10usly ~e utilized to provide a graphic-'' al dlsplay 100 of succe~sive voltage fluctuations indica-tive of heart activity and/or to provide a print out of an ECG at a prlnter 101 coupled to the computer or for other purposes. The data may, lf deslred, be ~tored on a disc - . . ~ , , :
, . :-,. ~ . .: . , .
by the computer 47.
FIGS. 6 through ll descrlbe a suitable detalled program for enabllng computer graphc display of data produced by the probe. FIG. 12 describes an alternate program which may also be used for the purpose.
~ he inventlon has been herein described with respect to the monitoring of heart activity but can also be used for monitoring voltage variations between spaced areas on a surface ln other contexts.
Whlle the lnventlon has been described with respect to a slngle preferred embodiment for purposes of example, many varlatlons ln the construction are possible and it is not intended to llmlt the invention except as defined in the ~ollowlng clalms.
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8ackaround of the Invention Electrocardiographs which visually display the heart actlvlty of llving sub~ects are well recognized to be of great value in the diagnos~s and treatment of medical patients. Instruments of this type are also useful for a number of other purposes such as ln the monitoring of cardlac act~vity in persons undergoing exercise training or for the display of an ECG for educational purposes.
The conventional electrocardiograph i8 a complex, costly and usually bulky assembly which must be operated by professional medical personnel or highly skilled technicians. Conseguently, usage of such equipment has more or less been restricted to hospitals, medical clinics, and medicial emergency vehicles. Compact and economical cardlac monltors have been developed but in general these produce only an audible signal or otherwise do not provide the type of data that is available f rom an ECG.
A more compact and economical cardiac monitor would be 3~ ' ,.
.
. , , - . :: ~ , . : ' ,.. . . . .
: --- , - ~ . .
highly advantageous not only in medical facilities but also for usage elsewhere. Such a device would for example, enable persons with cardiovascular problems to monitor their heart activity in their homes. Such apparatus should not require that the operator have specialized skills or undergo extensive training and should not expose the user to potential hazards such as electrical shock.
Instruments for obtaining electrocardiograms include spaced apart electrodes which contact the persons skin in the thoracic region in order to sense the minute voltage changes which accompany heart activity. The sensed voltage changes are amplified and displayed on the screen of an oscilloscope and/or are applied to a chart recorder or printer type of readout device to provide the electrocardiogram. The sensed voltage signals have also heretofore been digitized and transmitted to a computer which may variously be programmed to detect abnormal activity, to determine average values for specific phases of the cyclic heart activity or to analyze the data in a variety of other ways.
Prior computer aided heart monitoring systems do not resolve the problems discussed above. The computer typically functions only as a permanent component of the electrocardiograph and is not used for any other purpose.
Thus it further increases the cost and often the bulk of the heart activity monitoring installation. The prior computer aided systems, like older types of electrocardiograph/ require highly trained operators.
The present invention is directed to overcoming one or more of the problems discussed above.
.. .....
Summarv of the Invention In accordance with one aspect of the invention there is provided a unitary probe for producing and transmitting computer compatible serial form digital signals indicative of heart activity of a subject to a spaced apart digital computer of the general purpose type at which software may be changed by the operator to run any of a variety of different computer programs and which has a serial data input port, comprising: a probe housing having a configuration adapted for disposition at the thoracic region of said subject and having signal output means for transmitting said digital signals to said serial data input port of said computer; first, second and third electrodes secured to said housing and extending outward from a surface thereof, said electrodes being mutually spaced apart; first circuit means for producing a first analog signal which varies in accordance with variations of the electrical potential at said first electrode relative to the electrical potential at said third electrode: second circuit means for producing a second analog signal which varies in accordance with variations of the electrical potential at said second electrode relative to the electrical potential at said third electrode; third circuit means for producing a third analog signal which varies in accordance with variations of the difference between said first and second analog signals;
sign~l conversion circuit means for converting said third analog signal to sequences of serial form digital signal bits:
each of said circuit means being within said probe housing;
an electrical power supply disposed within said probe housing and being coupled to each of said circuit means to supply operating current thereto; and isolating means for transmitting said sequences of signal bits to said serial data input port of said computer through said output means of said probe housing and which converts said signal bits to non-electrical form and then back into electrical form to electrically isolate said subject from said computer.
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The invention provides a compact and economical instrument which enables minute voltage variations between spaced apart areas of a surface, such as the human skin, to be sensed and converted into serial form digital signals which may be applied to a personal computer to provide a visual display indicative of the voltage variations at the monitor screen of the computer. Among other uses, the invention enables unskilled persons to monitor their own heart activity away from medical facilities as the construction can be inexpensive, safe and easy to operate and connects to a commonly available display, a personal computer, rather than a specialized electrocardiograph.
, .
Brief Description of the Drawings FIG. 1 depicts a cardiac activity probe and an associated computer in accordance with a preferred embodiment of the invention.
FIG. 2 is an end view of the cardiac activity probe of FIG. 1 taken along line II-II thereof.
FIG. 3 is a schematic circuit diagram of electronic components of the probe of the preceding figures.
FIG. 4 is a detailed circuit diagram of the differential amplifier and band pass filter amplifier components of the probe which are shown in block form in FIG. 3.
; FIG. 5 is a detailed circuit diagram of the optical isolator and interface driver circuits shown in block form in FIG. 3.
:~ . .:
, FIGS. 6 through 11 described a detailed computer pro-gram for enabling computer graphic display of data produced by the probe of the preceding figures.
FIG. 12 describes another suitable computer program for displaying data transmitted to a computer by the probe.
FIG. 13 depicts a print out of an ECG from data produced by the probe.
, Detalled Descrlption of the Preferred Embodiment Referrlng inltially to FIGS. 1 and 2 of the drawings in con~unction, a cardiac probe unit 11 in accordance with this particular embodiment of the invention has a housing member 12 which includes a triangular plate portion 13 and thic~er housing 14 at one surface of the plate. The hous- -ing 14 contains electronic components which will herelnafter be descrlbed. Externally visible components of the housing 14 include a manually operable on-off switch 16, an openable battery compartment lid 17 and a signal output port 18.
Plate portlon 13 defines an isosceles triangle with a base 19 that 18 shorter than the sides 21. First, second and third electrodes, 22, 23 and 24 respectively, are sltuated at the ends of conductive support posts, 26, 27, and 28 respectively, which extend outward from the surface 29 of plate 13 that 18 opposite from houslng 14. First electrode 22 18 located at the apex of the trlangular plate 13 at ~hlch sldes 21 converge. Second electrode 23 is at the right hand slde of base ~9 when the probe 11 18 ln the operatlng orlentatlon shown ln the draw~ngs and third elec-trode 24 1~ at the left slde of the base.
In ~eeplng wlth the common termlnology ln the art, the flrst, second and th~rd electrodes 22, 23, 24 may be herelnafter referred to respectively as the right arm elec-trode, the left leg electrode and the right leg electrode.
Thls does not mean that the electrodes 22, 23, 24 contact those partlcular portions of the human body during use.
The trlangular plate 13 is proportioned to fit over the frontal thoraclal reglon of the human body with the right arm electrode 22 belng over the sternum 30, left leg elec-trode 23 belng over the lower ribs 31 at the left side of the body and rlght leg electrode being over the lower ribs at the right slde of the body.
Posltloning of the electrodes 22, 23, 24 over bony regions of the body allows flrmer pressure to be exerted and reduces artifact in the signals due to electrode .
-.. . ... ~ . .. ..
movement. Such placement also reduces signal degradation from non-cardial muscle actlvlty.
The spaclng of electrodes 22, 23, 24 from plate 13 by support posts 22, 23, 24 enables firm contact of the elec-trodes with the skln by accomodating to the convexity ofthe human chest. The trlangular configuration of the probe ll 18 particularly useful for women as it avoids the areas of the breasts.
Each electrode 22, 23, 24 preferably has a concave contact surface 32 and thus ls essentially cup shaped.
Pressure 18 then concentrated at a circle on the skin and this reduces electrical resistance and also reduces effects from body hair.
Referring now to FIG. 3, electronic components of the probe 11 include a first clrcuit stage 32 which is a low gain differential amplifler of the type havlng hlgh common mode re~ection. The first stage 32 has inputs 33 and 34 connected to the rlght arm electrode 22 and left leg electrode 23 respectively. The right leg electrode 24 in 20 effect const~tutes a chassis ground for the f~rst stage 32 and certain other components of the probe 11 as will here-inafter be described in more detail.
Fir~t Btage 32 produces a first analog signal indica-tive o~ voltage variations at right arm electrode 22 25 relatlve to the voltage at right leg electrode 24 and also produces a second analog slgnal indicative of voltage vari-atlons at left leg electrode 23 relative to the voltage at the right leg electrode and transmits a third analog signal lndicative of the difference between the first and second 30 analog signals to a second circuit stage 36. Sensing the voltage at electrodes 22 and 23 relative to the voltage at electrode 24 re~ects the effects of electrical artifacts, such as charges produced by nearby electrical equipment, which can appear on the body surface with a much larger 35 amplitude than ECG signals.
The second circuit stage 36 is a band pass amplifler which eliminates direct current and low frequency compon-ents of the thlrd analog signal to eliminate base line .. , ~ , . .. , . .......... , . , : .,, ........ ; . ~ -., , .
1 326~
drlft and whlch al80 ellmlnates high frequency components to further reduce electrlcal artifact such as resldual power line slgnals and signals generated by surface muscle activity. Stage 36 may typlcal ly be configured to transmit 5 only frequencies in the range from about 0.5 Hz to about 25 Hz. In this speclfic embodiment, the band pass amplifer 36 also æhifts the the signal amplitude from +/- one volt to 2.5 volts +/- one volt to accomodate to the input signal acceptance range of this particular third circuit stage 37.
The third circuit stage 37 is an analog to digital signal convertor which may be of known constructlon and receives the third analog signal from circuit stage 36.
The clock circuit 38 of this particular analog to digital convertor 37 causes sampling of the third analog signal at 15 a frequency of 250 Hz and transmits an eight bit digital output slgnal in parallel form at each such sampli,n,g.
The fourth circuit stage 39 is a parallel to serial digital slgnal convertor which may also be of known con-structlon. Convertor 39 converts the parallel elght blt 20 slgnals recelved slmultaneously on eight lnput lines 41 lnto sequent1al bit s~gnals whlch can be transmltted on a single output llne 42. The output slgnalllng rate in this partlcular embodlment is 9,600 bits per second.
Irhe serlal form signals from circuit stage 39 are 25 transmltted to the lnput circult 43 of an optical isolator or coupler 44 ~hich may also be of known internal cons-tructlon. ~he lnput clrcult 43 converts the serial slgnal blts from electrlcal to optical form and the output clrcu$t 46 of the isolator reconverts the optical slgnals back to 30 electrlcal signal bits. 'rhis electrical$y isolates the electrodes 22, 23, and 24 from the computer 47 to which the probe 11 i8 coupled thereby eliminating any risk of elec-trical shock as there is no electrically conductive path between such components.
Digitlzlng and serializing of the signals within the probe 11 prior to transmission of the signals through optical isolator 44 contributes substantially to the - : .
.
~- 1 326884 ob~ective of provldlng an inexpensive monltoring device.
Dlgltal optlcal lsolators 44 and partlcularly slngle channel lsolators are less costly than analog lsolators whlch must sensitlvely respond to slight differences in S signal voltage rather than to two distinctly different voltage levels as in the case of digital isolators.
The sequence of serlal slgnals from optical isolator 44 is transmltted to the output port 18 of probe unlt 11 through a computer lnterface drlver circult 48 within the the probe 11. Clrcuit 48 operates as an ampllfler and level shlfter which converts the signal voltages into the standardized range reguired for the serlal input ports 49 of personal computers 47.
A four conductor cable Sl provides for coupllng of the probe 11 output port 18 with the serial port 49 which is present on personal computers 47 for the purpose of-receiving digital eignals ln serial form from an external source. Cable Sl has a connector 52 at one end compatible ~ith the serial port 49 of the particular brand of computer 49 and ha~ a connector 53 at the other end that 18 engagable ~lth probe port 18 and which connects each of the standard ~our pins ~not shovn) o~ the computer serial port 49 with a ~eparate one of four contacts 54, 56, 57 and 58 of probe port 18. The probe port 18, mating connector 53 and cable Sl may, if de~ired, be of the low cost type u6ed for telephone recei~er installations as four conductors are used ln each case.
Cable Sl connects contacts 56 and 57 with the nreceive data~ and ~signal groundn pins, respectlvely of the computer serial port 49 and connects contacts 54 and 58 wlth the nterminal ready~ and ~transmit data" pins, respectively, of the computer port. Output signals from the interface dri~er 48 are transmitted to the computer 47 through contact 56 with contact 57 being the slgnal ground conductor.
It is a characterlstic of standard personal computer serlal ports 49 that a a D.C. voltage of +5 volts is .: , : ~ ~ . - ; .
, .
, - ~
- , . ~ : ~
-lo- 1 32~(8~
present on the "termlnal ready" pin durlng operation and a D.C. voltage o~ -5 volts i8 present at the "transmit data"
pin when lt 1~ not transmitting. These voltages are used to provide operatlng power for the interface driver 48 and output clrcult 46 of the optical isolator of the present ~nventlon by connecting the power terminals such circuits 48 and 46 across contacts 54 and 58.
The lnput clrcult 43 of optical isolator 44 and clrcult stages 36, 37, 38 and 39 are provided with an inde-pendent D.C. power source 59. In particular, the probe 11 includes a battery 61 connected to a voltage regulator 62 ln series wlth the probe on-off swltch 16. Regulato~ 62 has posltive and negative outputs B+ and B- whlch apply op-eratlng power, at constant voltages relative to the chassls ground deflned by right leg electrode 24, to clrcult stages 32 and 36. Only posltlve voltage from terminal B+ ~ 8 18 applled to stagee 37 and 39 and isolator lnput clrcuit 43 whlch do not require blpolar power ln thls embodlment.
Use of D.C. voltage derlved from the computer 47 for operating th~ lnter~ace drlver 48 and output clrcult 46 of optical. lsolator 43 while the other components of the probe 11 operate fro~ ~n lndependent self-contalned power 8upply 59 re6ults ln there belng no electrlcally conductive path between the co~puter 47 and the electrodes 22, 23, 24. ThUE;
the computer 47 18 not a source of possible electrlcal shock and cant transmlt signal artifact to the electrodes.
FIG. 4 deplcts ~ultable clrcuit detail for the first and second clrcult stageB 32 and 36. In particular, right leg electrode 22 and left leg electrode 23 are connected to the non-invertlng inputs of a first palr of ampllflers 63 and 64 resp~ctlvely whlch ampllfy the mlnute voltages that are sensed by the electrodes. The output of ampllfier 63 18 connected to the output of ampllfier 64 through three - serles connectod resistors 66, 67 and 68. The circuit ~unctlon 69 between resistors 66 and 67 18 connected to the inverting input of ampllfler 63 and the clrcuit junction 71 between resistors 67 and 68 connects to the inverting lnput ,: , ., - ;,., ,' , ' ; - ~ , . .
.
of amplifier 64.
The amplified voltage signals from amplifiers 63 and 64 are respectively applled to the inverting and non-in-verting lnputs of a dlfferentlal amplifier 73 through input re61stors 74 and 76 respectively. A feedbac~ resistance 77 is connected across the lnverting input and output of amp-lifier 73 and an ad~ustable resistance 78 is connected between the non-lnvertlng lnput and ground. Resistanc~ 78 may be ad~usted to compensate for offset in amplifier 73 and to nu~l any common mode output.
~ he flrst and second analog signal voltages produoed by ampllflers 63 and 64 are proportional to the voltages sensed by electrodes 22 and 23 respectively at any glven time. Differentlal ampllfier 73 produces a third analog ~ignal voltage ~hlch varles ln accordance wlth variatlons of the dlfference between the flrst and second analog signals.
~ he secona clrcuit stage 36 or band pass fllter amp-llfier may include another ampllfier 79 havlng a non-ln-verting lnput coupled to the output of the dlfferentlal ampllfler 73 through a capacltor 81 and which 18 also connected to ground through a reslstor 82. Capacltor 81 and resl~tor 82 form a hlgh pass fllter whlch blocks dlrect current and supresses low rrequency slgnal varlatlons.
Another reslstor 83 and capacltor 84 are connected ln parallel across the lnvertlng lnput and output of amplifler 79 and functlon as a hlgh pass fllter which eliminates hlgh ~requency artlfact from the slgnal. An additlonal reslstor 86 connected between the lnverting lnput and ground operates ln con~unctlon ~lth reslstor 83 to establish the galn of the ampllfler 79 to provlde a signal voltage range compatlble wlth the partlcular analog to dlgital convertor 37 to ~hlch the ampllfler 18 coupled. Reslstor 85 whlch connect~ the lnvertlng lnput to B- provides offset.
aeferrlng now to FIG. 5, the input circuit 43 of optlcal lsolator 44 has a llght emlttlng dlode 87 connected between the power source terminal B+ and ground in series with a resistor 88 and receives the serial form digital ,:
.
: .:
1 732b~8~
slgnals from parallel to serial signal convertor 39 at the circult ~unction bet~een the diode and re~istor. The output circult 46 of lsolator 44 lncludes a photosensltive transl6tor 89 of the type ~hich exhlblts a variable gain ln response to changes ln the llght output of dlode 87 produced by the lncoming signals.
The interface drlver 48 may have still another amplif-ier 91 which has an output connected to the receive data contact 56 of the pro~e output port 18. The positive and negatlve pover lnputs of amplifier 91 are respectively connected to the transmit data contact 58 and terminal ready contact 54 of the output port 18 to supply operating voltage derlved from the computer. A capacitor 92 ls con-nected across 57 and 58 and another capacitor 93 is con-nected across contacts 54 and 57 to provide energy storage for the relatlvely hlgh impedance power supply form"ed by ,transmlt data and data terminal ready pins of the computer port.
The photosenslt1ve translstor 89 of optlcal lsolator 44 18 connected acro~s contacts 57 and 58 ln serles wlth a flxed res1~tor 94. The non-lnvertlng lnput og amplifler 91 connect~ to the clrcult ,~unctlon 96 between reslstor 94 and photosensltlve transistor 89 and also connects to ground contact 57 through a palr of 6eries resi6tors 97 and 98.
The lnvertlng lnput o~ the amplifier 91 connects to the clrcult ,~unctlon 99 bet-reen resistors 97 and 98.
Ampli~ler 91 ln con~unction ~,rith resistors 97 and 98 act~ as a co~parator whlch converts the voltage varlations across photosen~ltlve transistor 89 to a voltage range that 30 is compatlble ~lth the computer, for example to +/- 5 ' ' volts ~or the EIA RS-232 format.
Re~err~ng agaln to FIG. 1, the signals transmitted to computer 47 ~ay var10usly ~e utilized to provide a graphic-'' al dlsplay 100 of succe~sive voltage fluctuations indica-tive of heart activity and/or to provide a print out of an ECG at a prlnter 101 coupled to the computer or for other purposes. The data may, lf deslred, be ~tored on a disc - . . ~ , , :
, . :-,. ~ . .: . , .
by the computer 47.
FIGS. 6 through ll descrlbe a suitable detalled program for enabllng computer graphc display of data produced by the probe. FIG. 12 describes an alternate program which may also be used for the purpose.
~ he inventlon has been herein described with respect to the monitoring of heart activity but can also be used for monitoring voltage variations between spaced areas on a surface ln other contexts.
Whlle the lnventlon has been described with respect to a slngle preferred embodiment for purposes of example, many varlatlons ln the construction are possible and it is not intended to llmlt the invention except as defined in the ~ollowlng clalms.
' . ' .:
. ~ , .
.. . .
Claims (8)
1. A unitary probe for producing and transmitting computer compatible serial form digital signals indicative of heart activity of a subject to a spaced apart digital computer of the general purpose type at which software may be changed by the operator to run any of a variety of different computer programs and which has a serial data input port, comprising:
a probe housing having a configuration adapted for disposition at the thoracic region of said subject and having signal output means for transmitting said digital signals to said serial data input port of said computer;
first, second and third electrodes secured to said housing and extending outward from a surface thereof, said electrodes being mutually spaced apart;
first circuit means for producing a first analog signal which varies in accordance with variations of the electrical potential at said first electrode relative to the electrical potential at said third electrode;
second circuit means for producing a second analog signal which varies in accordance with variations of the electrical potential at said second electrode relative to the electrical potential at said third electrode;
third circuit means for producing a third analog signal which varies in accordance with variations of the difference between said first and second analog signals;
signal conversion circuit means for converting said third analog signal to sequences of serial form digital signal bits;
each of said circuit means being within said probe housing;
an electrical power supply disposed within said probe housing and being coupled to each of said circuit means to supply operating current thereto; and isolating means for transmitting said sequences of signal bits to said serial data input port of said computer through said output means of said probe housing and which converts said signal bits to non-electrical form and then back into electrical form to electrically isolate said subject from said computer.
a probe housing having a configuration adapted for disposition at the thoracic region of said subject and having signal output means for transmitting said digital signals to said serial data input port of said computer;
first, second and third electrodes secured to said housing and extending outward from a surface thereof, said electrodes being mutually spaced apart;
first circuit means for producing a first analog signal which varies in accordance with variations of the electrical potential at said first electrode relative to the electrical potential at said third electrode;
second circuit means for producing a second analog signal which varies in accordance with variations of the electrical potential at said second electrode relative to the electrical potential at said third electrode;
third circuit means for producing a third analog signal which varies in accordance with variations of the difference between said first and second analog signals;
signal conversion circuit means for converting said third analog signal to sequences of serial form digital signal bits;
each of said circuit means being within said probe housing;
an electrical power supply disposed within said probe housing and being coupled to each of said circuit means to supply operating current thereto; and isolating means for transmitting said sequences of signal bits to said serial data input port of said computer through said output means of said probe housing and which converts said signal bits to non-electrical form and then back into electrical form to electrically isolate said subject from said computer.
2. The probe of claim 1 wherein said isolation means includes an optical isolator coupled between said signal conversion circuit means and said output means.
3. The probe of claim 2 wherein said optical isolator has an electrically energized signal input circuit in which said signal bits are converted from electrical form to optical form and has an electrically energized signal output circuit in which said signal bits are converted back to electrical form and wherein said serial data input port of said computer includes a conductor having a direct current voltage thereon, further comprising:
means for energizing said output circuit of said optical isolator from said conductor of said serial data input port of said computer; and means for independently energizing said input circuit of said optical isolator from said electrical power supply.
means for energizing said output circuit of said optical isolator from said conductor of said serial data input port of said computer; and means for independently energizing said input circuit of said optical isolator from said electrical power supply.
4. The probe of claim 1 wherein said signal conversion circuit means includes:
an analog to digital signal convertor having a signal input coupled to said third circuit means for receiving said third analog signal there from and having a signal output for transmitting a corresponding signal in parallel digital form;
a parallel to serial digital signal convertor having signal inputs coupled to said output of said analog to digital signal convertor for receiving said parallel form signal therefrom and having an output for transmitting said signal in serial form.
an analog to digital signal convertor having a signal input coupled to said third circuit means for receiving said third analog signal there from and having a signal output for transmitting a corresponding signal in parallel digital form;
a parallel to serial digital signal convertor having signal inputs coupled to said output of said analog to digital signal convertor for receiving said parallel form signal therefrom and having an output for transmitting said signal in serial form.
5. The probe of claim 4 wherein said isolating means includes an optical isolator coupled between said output of said parallel to serial signal convertor and said output means of said probe housing.
6. The probe of claim 5 further including a computer interface driver circuit located in said probe housing said optical isolator being coupled to said output means through said interface driver circuit.
7. The probe of claim 1 wherein said probe housing has a substantially isosceles triangle configuration with sides that are longer than the base, said second and third electrodes being situated at the apexes which are at said base and said first electrode being situated at the apex which is remote from said base.
8. A unitary probe for detecting voltage variations at the thoracic region of a subject and for transmitting computer compatible serial form digital signals indicative of said voltage variations to a spaced apart general purpose digital computer of the type at which programming can be changed by the operator and which has a serial data input port, said serial data input port having a conductor at which a direct current voltage is present, comprising:
a probe housing having a configuration adapted for emplacement of said housing at said thoracic region of said subject and having a signal output port for connection to said serial data input port of said computer;
first, second and third mutually spaced apart electrodes extending outward from said probe housing for contact with said surface;
first circuit means for producing a first analog signal indicative of voltage at said first electrode relative to the voltage at said third electrode;
second circuit means for producing a second analog signal indicative of voltage at said second electrode relative to the voltage at said third electrode;
third circuit means for producing a third analog signal indicative of the difference between said first and second analog signals:
fourth circuit means for converting said third analog signal into parallel form digital signals:
fifth circuit means for converting said parallel form digital signals into serial form digital signals:
each of said circuit means being disposed within said probe housing;
an optical isolator within said probe housing, said optical isolator having an input side coupled to said fifth circuit means to receive said serial form digital signals and having an output side for transmitting said serial form digital signals;
a computer interface driver disposed within said probe housing and being coupled between said output said of said optical isolator and said signal output port of said probe housing to transmit said serial form digital signals thereto;
a direct current power supply disposed in said probe housing and being coupled to each of said circuit means and to said input side of said optical isolator to supply operating current thereto, and means for connecting said conductor of said computer serial data port to said output side of said optical isolator and to said interface driver to supply operating current thereto.
a probe housing having a configuration adapted for emplacement of said housing at said thoracic region of said subject and having a signal output port for connection to said serial data input port of said computer;
first, second and third mutually spaced apart electrodes extending outward from said probe housing for contact with said surface;
first circuit means for producing a first analog signal indicative of voltage at said first electrode relative to the voltage at said third electrode;
second circuit means for producing a second analog signal indicative of voltage at said second electrode relative to the voltage at said third electrode;
third circuit means for producing a third analog signal indicative of the difference between said first and second analog signals:
fourth circuit means for converting said third analog signal into parallel form digital signals:
fifth circuit means for converting said parallel form digital signals into serial form digital signals:
each of said circuit means being disposed within said probe housing;
an optical isolator within said probe housing, said optical isolator having an input side coupled to said fifth circuit means to receive said serial form digital signals and having an output side for transmitting said serial form digital signals;
a computer interface driver disposed within said probe housing and being coupled between said output said of said optical isolator and said signal output port of said probe housing to transmit said serial form digital signals thereto;
a direct current power supply disposed in said probe housing and being coupled to each of said circuit means and to said input side of said optical isolator to supply operating current thereto, and means for connecting said conductor of said computer serial data port to said output side of said optical isolator and to said interface driver to supply operating current thereto.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/095,314 US4858617A (en) | 1987-09-10 | 1987-09-10 | Cardiac probe enabling use of personal computer for monitoring heart activity or the like |
| US95,314 | 1987-09-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1326884C true CA1326884C (en) | 1994-02-08 |
Family
ID=22251334
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000576941A Expired - Fee Related CA1326884C (en) | 1987-09-10 | 1988-09-09 | Cardiac probe enabling use of personal computer for monitoring heart activity or the like |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4858617A (en) |
| AU (1) | AU2530288A (en) |
| CA (1) | CA1326884C (en) |
| WO (1) | WO1989002247A1 (en) |
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-
1987
- 1987-09-10 US US07/095,314 patent/US4858617A/en not_active Expired - Lifetime
-
1988
- 1988-09-08 AU AU25302/88A patent/AU2530288A/en not_active Abandoned
- 1988-09-08 WO PCT/US1988/003086 patent/WO1989002247A1/en unknown
- 1988-09-09 CA CA000576941A patent/CA1326884C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US4858617A (en) | 1989-08-22 |
| AU2530288A (en) | 1989-04-17 |
| WO1989002247A1 (en) | 1989-03-23 |
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