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HANNING FILTER: A(0) = 1/4 [X(0) + 2X(-1) + X (-2) ]
FIRST ORDER HIGH PASS UR FILTER:
HIGH PASS = SIGNAL-LOW PASS
C (0) = A (0) - B (0) / m WHERE
m = 4 AND B (0) = A (-4) - A (0) - B (-1)
FILTER FREQUENCY = 3 db @ 9 Hz.
HANNING FILTER: D (0) = 1/4 [C(0) + 2G (-1) + C(-2)]
FIRST ORDER HIGH PASS IIR FILTER:
HIGH PASS = SIGNAL - LOW PASS
F (0) = D (0) - E (0) / m WHERE
m = 4 AND E (0) = D (-4) - D (0)-E (-1)
FILTER FREQUENCY = 3 db @ 9 Hz.
WRIST WORN ECG MONITOR
This is a divisional continuation of application Ser. No. 07/816,389 filed Dec. 26,1991 now U.S. Pat No. 5 5,289,824.
BACKGROUND AND SUMMARY OF THE
The invention generally relates to wrist-worn cardiac 10 monitors. More particularly, the invention concerns a wrist-worn ECG monitor having integral electrodes for recording and teletransmitting ECG data to a remote site for analysis by a diagnostician.
Known wrist-worn cardiac monitors are extremely 15 limited in functionality. For example, some conventional monitors simply monitor and display pulse rate and thus provide no ECG data recording capability at all. Others record ECG data and provide only for the local playback of recorded data and thus provide no 20 remote diagnostic capability. Still others require external electrodes on the ends of a cable for detection of an ECG signal near the heart of the cardiac patient—often necessitating the use of messy conductive gels—and thus are difficult to hook up and use, especially for 25 long-term monitoring of a relatively active patient. Problems abound in producing small, lightweight ECG monitors that provide for long-term cardiac event recording and remote professional diagnostic and prescriptive patient care. 30
Accordingly, it is a principal object of the present invention to provide a self-contained, wrist-worn ECG monitor that provides at least single event recording and telecommunication of ECG data to a remote site for professional diagnosis. 35
It is another important object of the invention to provide such a monitor with the greatest possible functionality in an extremely compact, integral housing.
Yet another object is to provide such a monitor that reliably detects and records ECG signals without the 40 use of external electrodes or messy gels or other skin preparation.
It is also an object of the invention to provide an improved dry skin electrode system that is an integral part of the housing of such a monitor. 45
Another object is to render such a wrist-worn monitor that easily and conveniently can be used by a cardiac patient without assistance by another, for long-term ambulatory patient care.
Still another object is to make such a wrist-worn 50 ECG monitor the multiple functions of which readily can be operated with the patient's other hand.
One equally important object is to provide such functionality in a lightweight, compact, wrist-worn monitor that yet has the capacity to record multiple events that 55 may occur over a long period of time, e.g. days.
One other object of the invention is to make such a monitor easily manufactured and maintained, and cost effective.
Briefly summarizing the invention in its preferred 60 embodiment, a wrist-worn monitor is provided that, without external connections of any kind, enables local, multiple event ECG data recording and telecommunication to a remote site, as well as providing the time and date functions normally provided by a wristwatch. The 65 monitor is housed in an extremely compact and lightweight housing and is operable by the patient's simply placing the other palm over a portion of the monitor's
face to contact an upper skin electrode. Custom verylarge-scale integrated (VLSI) circuit components contained within the housing include ECG signal and abnormal event detection circuitry, analog-to-digital (AD) and digital-to-analog (DA) conversion circuitry, memory and processor circuitry for scanning the pushbuttons and displaying selected chronometric, cardiac and status information. Circuitry is also provided to drive an integral speaker for the telecommunication of ECG signal or cardiac event data via telephone lines to a remote site for so-called "over-read" diagnosis and archival recording
The monitor's housing includes dual, integral dry skin electrodes located on a wrist-contacting, inner or rear base plate and on an outer or front surface contactable by the palm of the patient's other hand. The electrodes preferably are formed by plating a region of a stainless steel or other base metal expanse with a thin layer of titanium nitride (TiN), titanium carbide (TiC) or titanium carbo-nitride (TiCN). The microprocessor and associated electronics, including firmware executed thereby, employs a digital bandpass filter reliably to detect ECG signals characterized by QRS complexes or pacer and defibrillator pulses but to ignore noise and motion artifacts. A current draw measuring method implemented by the microprocessor and associated electronics monitors usage and predicts the end of life of the integral battery beyond which monitoring is halted, thereby to maximize long-term monitoring capacity, to avoid potentially inaccurate ECG data recording and to inform the patient when the battery should be replaced.
These and other objects and advantages of the invention will be more clearly understood from a consideration of the accompanying drawings and the following description of the preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of the wrist-worn ECG monitor made in accordance with the preferred embodiment of the invention.
FIG. 2 is an exploded frontal isometric view of the ECG monitor corresponding with that of FIG. 1, with the wrist band removed for clarity.
FIG. 3A is an exploded isometric view of the ECG monitor corresponding with that of FIG. 2, but showing it generally from the rear instead of the front.
FIG. 3B is an enlarged, fragmentary cross-sectional view of the lower electrode shown in FIG. 3A.
FIG. 4 is a schematic block diagram of the monitor shown in FIG. 1.
FIG. 5 is a flowchart illustrating the battery life prediction method of the invention.
FIG. 6 is a flowchart illustrating the digital filtering method of the invention.
DETAILED DESCRIPTION OF THE
Referring first and briefly to FIG. 1, the apparatus of the invention made in accordance with its preferred embodiment is indicated in isometric view at 10. It may be seen from FIG. 1 that apparatus 10, which is drawn generally in enlarged but otherwise accurate scale, is am extremely compact and lightweight, extremely full function cardiac monitor that conveniently and comfortably can be wrist-worn by a cardiac patient, because the form factor and size of the monitor's housing relative to the conventional wrist band is only slightly
larger than a traditional digital watch. The full functionality of apparatus 10, which provides unprecedented functional density and convenience due to its fully integrated dry skin electrodes, will be described in detail by reference to FIGS. 2-6. 5
Referring now to FIG. 2, apparatus 10 is shown in exploded isometric view. Wrist-worn ECG, or cardiac data, monitoring apparatus 10 comprises a housing 12 including first and second dry skin electrodes 14, 16 unitarily connected therewith and forming an integral 10 part thereof for making conductive contact with a cardiac patient's skin surface and a bezel 18 (with associated gasket 18a) also forming an integral part thereof; plural pushbutton switches 20, 22, 24, 26 (with associated O-ring gaskets 20a, 206, 22a, 22b, 24a, 246, 26a, 15 26b); a conventional watchband 28 of any suitable size and structure (see FIG. 1); and, entirely contained within housing 12, electronics indicated generally at 30.
Turning briefly to FIG. 4, electronics 30 include an ECG signal amplifier 32 including hardware filters 34 20 coupled with electrodes 14,16 for producing an analog signal representative of the electrical field on the surface of the patient's skin and between electrodes 14,16. Electronics 30 also include analog-to-digital signal conversion means, or analog-to-digital converter (ADC), 25 36 connected with amplifier 32 for producing digital data representing the patient's ECG waveform over a predefined interval of time. Electronics 30 preferably include 32-kilobytes (32-kb) of static read-and-write memory (SRAM) 38 that operates as means for record- 30 ing digital data produced by ADC 36. Electronics 30 also include means 40 (preferably including a microcontroller with 8-kb of read-only memory (ROM) 42, a digital-to-analog converter (DAC) 44, a voltage-controlled oscillator (VCO) 46 and a speaker 48) for wire- 35 lessly, and preferably audibly, communicating data recorded in SRAM 38 to a remote site for verification or so-called "over-read", real-time diagnosis and/or archival recording.
Because in its preferred embodiment wrist-worn car- 40 diac data monitor 10 comprises electronics 30 providing at least all of the functions described immediately above, an extremely high level of functional density is achieved by the invention. By functional density is meant a measure of the functionality per unit volume, 45 whether the volume is that contained within housing 12 or is that contained within and including housing 12 (of which electrodes 14,16 form an integral part: electrode 14 integrally molded therein and electrode 16 by the use of screws S turned into corresponding tapped holes 50 formed therein). In accordance with the preferred embodiment of the invention, and as measured by conventional water displacement means, the interior, or contained, predetermined volume within housing 12 does not exceed approximately 0.75 -inches3, and is prefera- 55 bly equal to or less than approximately 0.625-inches3. Similarly measured, the exterior predetermined volume within and including housing 12 (and integral electrodes 14, 16 and bezel 18) does not exceed approximately 15-inches3 and is preferably equal to or less than approx- 60 imately 1.25-inches3.
Dry skin electrodes 14, 16 are designed for use with equipment capable of producing or monitoring changing electrical conditions (indicative of changing cardiography conditions) at the surface of a patient's skin, and 65 are particularly suitable in cardiac monitoring, e.g. by apparatus 10. As illustrated in FIG. 3B, an electrode such as electrode 14 preferably comprises an expanse
14a formed of a base metal such as stainless steel, with expanse 14a being electrically connectable with such monitoring equipment, as illustrated in FIGS. 1 and 2. Plating an outer, skin-contactable region or surface 14a' of expanse 14a is a composition 146 (shown in greatly enlarged thickness in FIG. 3B relative to that of expanse 14a) including a first component of a preferably biocompatible, conductive (e.g. metallic) element such as titanium, and at least a second component chosen from a group including nitrogen and carbon. It will be understood that electrode 16 of apparatus 10 is of identical material content and cross-sectional structure as electrode 14, but is of much greater surface area.
Those of skill in the arts will appreciate that such electrode 14 might be connectable with stimulus/response equipment by any suitable means including an electrical conductor or wire, e.g. the coil spring used in connection with apparatus 10 having such electrode 14 integrally housed therewith. Those skilled also will appreciate that such electrode 14 comprising such plated expanse obviates use of a messy, conductive gel, and even the so-called "residue-free" self-adhesive gelatinous pads that often are used to enhance conductivity between an electrode and a patient's skin. Finally, those of skill in the arts will appreciate that stimulus/response equipment with which such invented electrode 14 is believed to be useful includes not only electrical conditions change-monitoring, or response, equipment but also electrical conditions change-producing, or stimulus, equipment such as neural, muscular or other anatomical electrostimulation equipment.
Preferably base metal-plating composition 146 is in order of preference a titanium nitride (TIN), titanium carbide (TiC) or titanium carbo-nitride (TiCN) layer approximately 3-microns (0.003-inch) thick. Such composition can be plated by known chemical or physical vapor deposition techniques, and preferably the plating composition is polished to a smooth finish primarily for aesthetic reasons. Such plating of base metal expanse 14 a has been found to protect, and thus to greatly extend the life, of a dry skin electrode such as electrode 14 by producing an extremely hard, exterior, skin-contactable surface. Such plating also has been found to provide high conductivity and thus to produce a high quality electrical interface between an electrode such as electrode 14 and the patient's skin surface, which may be very dry
Referring now briefly to FIGS. 2 and 3A, necessary details of the structure of apparatus 10 made in accordance with its preferred embodiment will be described. Electronics 30 may be seen to be implemented preferably in various discrete and integrated circuits surfacemounted or ultrasonic wire bonded onto a multi-layer printed circuit board (PCB) 50 supported within housing 12 by a perimeter support member 52. Thus, PCB 50, which preferably comprises plural adhered, copperclad epoxy layers, may be seen physically to mount and interconnect the various circuitry shown schematically in FIG. 4, including on its bottom side a microcontroller (with integral ROM) chip 42, interconnecting and mounting support members 54a, 546 for connection with one terminal of battery B, a double-leaf spring member 56 for connection with the other terminal of battery B and a "land" or circuit pad, 58 for connecting lower electrode 16 via a coil spring 60 to one signal input terminal of ECG amplifier 32.
Upper electrode 14 is connected to the other signal input terminal of ECG amplifier 32 via a generally