AU1241888A - Portable physiological monitor - Google Patents

Description

PORTABLE PHYSIOLOGICAL MONITOR FIELD OF INVENTION The present invention relates to a portable monitor and, in particular, to a portable monitor suitable for acquiring, analysing, storing and displaying vital physiological signs.

BACKGROUND OF THE INVENTION Prior art devices for obtaining and recording vital physiological signs exist. However, the devices have tended to be specialised devices designed typically for only one physiological sign. Also, the majority of the devices have not been truly portable.

Typically therefore, in practice, particularly in hospital situations, a plurality of instruments is used in order to obtain information concerning the physiological status of the patient. Some of these instruments are attached to free standing equipment and require cables for inter-connection from the patient to the separate free standing devices.

Known prior art includes US 4,606,352 to Geddes et al. This specification discloses a "pocket-sized, self-contained electrocardiogram monitor with a dot-matrix, liquid-crystal display". This unit is limited to sensing and display of ECG signals only. Whilst useful, an ECG waveform is but one of the vital signs available from the human body. A multiplicity of vital signs is typically required to be monitored for medical personnel to obtain a clear understanding of a patient's condition. GB 2,142,727 to Turner et al discloses a similar device which suffers from the same drawbacks associated with limited presentation of information.

US 3,848,582 to Milani et al and US 3,858,576 to Dehnert et al disclose similar but cruder devices.

US 4,250,889 to Levin, US 4,230,127 to Larson, US 3,792,700 to Sarnoff and US 4,083,366 to Gombrich disclose dedicated devices for monitoring ECG which are designed to be worn by a user for extended periods of time or otherwise require some form of semi-permanent connection to the user.

There is a great deal of prior art available concerning detailed aspects of the processing of ECG signals and the display of those signals. Representative specifications include US 3,809,071 to Davolos et al, US 4,346,378 to Shanks and US 4,250,503 also Shanks.

Distortion of waveforms, intentional or otherwise, has not always been considered from the user's point of view in the prior art.

The manner in which information is communicated to the user is also very important. For example medical personnel have made use of conventional stethoscopes for many years and have been trained in and are used to interpreting sounds from conventional stethoscopes. Similarly medical practitioners have been trained and have become skilled in interpreting "unprocessed" ECG signals obtained directly from the patient and displayed on a high resolution monitor. It is important, even if the technology by which the information is obtained varies, that the information be continued to be presented in a way which allows the practitioner to use experience already gained on prior art instrumentation. It is an object of the present invention to provide a monitoring device which is portable and which is adapted to measure and display a plurality of vital signs at the same time.

It is a further object of the present invention to provide a monitoring device which, whilst using electronic aquisition equipment, none theless, presents information to the experienced user in such a way that previous experience obtained on prior art instrumentation can be utilised.

Finally, it is an object of the present invention to provide a portable monitor capable of monitoring a plurality of vital physiological signs which will substantially overcome, or ameliorate, the above mentioned disadvantages.

SUMMARY OF THE INVENTION

In one broad form there is provided a portable, self-contained, physiological monitor said monitor including multifunctional electrodes arranged in a planar configuration on a first surface of said monitor, said monitor further including data processing means to receive and analyse signals received from said multifunctional electrodes, said monitor further including output means to output information analysed by said data processing means to a user, said monitor adapted to sense and display a plurality of vital signs at the same time in real time. Preferably said multifunctional electrodes comprise first, second and third electrodes arranged in planar, triangular configuration.

Preferably said first electrode includes a sound sensor and said second electrode includes a thermal sensor.

Preferably all sides of said planar, triangular configuration are less than 10 cm.

Preferably said electrodes at a skin contacting surface have a diameter in the range 1.5 cm to 3.5 cm.

Preferably said output means includes a video display adapted to display ECG waveforms and digital data.

Preferably said electrodes comprise stainless steel, more preferably with a platinum coating on skin contacting surfaces.

Preferably information is sampled at at least 200 Hz in order to provide information acquisition at a diagnostic quality bandwidth of 100 Hz.

Preferably said video display comprises a LCD display having an effective bandwidth of approximately 50 Hz.

In a further preferred form there is provided a method of monitoring the vital signs of a living human being comprising applying a portable physiological monitor to a chest region of a patient, said monitor comprising a portable, self-contained, physiological monitor said monitor including multifunctional electrodes arranged in a planar configuration on a first surface of said monitor, said monitor further including data processing means to receive and analyse signals received from said multifunctional electrodes, said monitor further including output means to output information analysed by said data processing means to a user, said monitor adapted to sense and display a plurality of vital signs at the same time in real time.

In accordance with yet a further aspect of the present invention there is provided a portable physiological monitor comprising three electrodes in a planar, triangular, configuration, together with data processing means to analyse signals received from said electrodes and output means to output analysed information to a user, said monitor adapted to sense and display a plurality of vital signs at the same time in real time.

In one preferred form, said triangular configuration is an isosceles triangular configuration with a reference electrode forming an apex of said isosceles triangular configuration.

Preferably said device further includes additional physiological sensors including a sound sensor and/or a thermal sensor.

Preferably, said additional physiological sensors are embedded in a skin contacting surface of one or more of said electrodes.

Preferably, all sides of said triangular configuration are less than 10 cm.

Preferably, the diameter of said electrodes at a skin contacting surface is in the range 1.5 cm to 3.5 cm.

Preferably, said output means includes a video display to display ECG waveforms and digital data. DRAWINGS

Embodiments of the present invention will now be described with reference to the drawings in which :

Figure 1 discloses an idealised ECG waveform;

Figure 2 discloses a functional block diagram of the preferred embodiment;

Figure 3 discloses the external features of a first preferred embodiment; and

Figure 4 shows a typical output on the video output device of the first preferred embodiment.

Figure 5 discloses the external features of a second preferred embodiment;

Figure 6 shows a typical output on the video output device of the second preferred embodiment;

Figure 7 shows a hardware based block diagram of the second embodiment;

Figure 8 shows block schematic diagrams of input buffer circuits suitable for use with either the first or second embodiment;

Figure 9 shows a software logic flow diagram for the ECG and heart rate display;

Figure 10 shows a software logic flow diagram for the respiration display; and

Figure 11 shows the software logic flow diagram for the temperature display suitable for programming of either the first or second embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To set the context of the invention Figure 1 shows an idealised ECG waveform. The dominant features P, Q, R, S, T and the relationship between them is used by ECG monitoring equipment and medical personnel skilled in interpretation to give an indication of the behaviour of a patient's heart beat. The device of the first and second preferred embodiments of the present invention analyses the features of this waveform according to algorithms known in the art as well as presenting the specific patients waveform as sensed on a video display forming part of the unit of either the first or second embodiments. Additionally, the device of either the first or second preferred embodiments senses other vital signs at the same time. These other vital signs are also displayed on the video display device in real time.

To place the device of the preferred embodiment in context, it should be noted that whilst ECG sensing systems have been available in the past, these typically have required the attachment of separate electrodes to the body. The device of the present invention allows one unit to be placed upon the body and directional ECG waveforms and other waveforms to be displayed on that same unit. This is in part due to the compact, offset electrode configuration of the device. The multifunctional electrodes further allow a plurality of physiological signs to be obtained and displayed at the same time, in real time, thereby providing a powerful diagnostic tool. Referring to Figure 2 the device, 1, of the first and second preferred embodiments can be described functionally as follows:

Physiological Sensors Block (2)

The device acquires various physiological signals from the living body by way of sensor/buffer circuits 22 (not shown), which are displayed and analysed in real time. The sensors which connect to the body to gather these signals consist of three multifunctional sensors which are placed against the external skin of the chest wall. These sensors combine the function of ECG electrodes to detect the electrical signal of the heart, a microphone to detect heart sounds, a thermal sensor to measure temperature and an impedance measuring technique to sense respiration.

Signal Conditioning Block (3)

The various electrical signals from the sensors need to be amplified and filtered, in order to be converted into digital information for later measurement and display. This block will also exclude any extraneous signals or noise. Processed signals are provided to external output block 21 for sending to external devices such as stethoscope, printer, medium, computer, etc.

Analog - Digital Conversion Block (4)

The analog electrical signals are converted to digital information which can then be more readily processed.

Measurement and Calculation Block (5)

The digital information derived from the original physiological signals needs to be processed to display parameters which are useful to the user. The heart rate is calculated by measuring the average period of the ECG. The respiration rate is calculated by measuring the average period of the respiration signals. The temperature must be scaled appropriately so the temperature in degrees can be displayed.

Display Block (6) The waveforms and calculated values need to be available to the user. The function of this block is to display on a screen, (preferably a high resolution dot matrix LCD display) the various analog waveforms as traces on a screen, and the calculated values as numerals on the same screen. In addition, the screen can be used to warn the user of faults or problems, and of the current mode of operation. Previously stored information can also be recalled to the screen for further analysis by the user. The LCD screen has a rectangular arrangement of 240 picture elements by 220 picture elements arranged on a 2 inch diagonal display. The display is updated at a sweep rate of 12.5 mm per second. Suitable display units can be obtained from manufacturers such as EPSOM, CASIO and TOSHIBA.

Storage Block (7)

Waveforms and calculated values are stored in memory to allow later recall by the user, either to make a hard copy on a printer, which is connected via the external output, or to re-display them on the screen for further analysis.

Control Block (8)

The integrated operation of the various other blocks is controlled by this block. The user controls the operation of the device via control switches 9 which indicate to the control microprocessor exactly what signals need to be acquired, processed and displayed.

FIRST EMBODIMENT

Referring to Figure 3 the predominant external features of a first embodiment of the device are disclosed. These include electrodes 11, 12, 13 protruding from case 18. The skin contacting portions of the three electrodes 11, 12, 13 lie in the one plane. Electrode 11 incorporates a microphone 19. The receiving surface of the microphone lies flush with the skin contacting surface of the electrode 11. The microphone is arranged to pick up bodily sounds including heart and lung sounds. Electrode 13 incorporates a thermal sensor 20, for example a thermistor. Again, the sensing surface of the thermal sensor lies flush with the skin contacting surface of the electrode 13. The thermal sensor 20 can thus provide an indication of skin/body temperature whilst electrode 13 is in contact with the skin.

Preferably, electrode 12 is a reference electrode however any one of the electrodes can be used as a reference electrode so as to provide electrical signal directional sensitivity for ECG readings.

Electrodes 12 and 13 have a diameter of approximately 1.8 cm whilst electrode 1 has a diameter of approximately 3.2 cm at the skin contacting surface. The distance between centres of electrodes 11 to 12 and 12 to 13 is 6 cm whilst the distance between electrodes 11 to 13 is 3.5 cm between centres.

The casing 18 also houses a speaker 6 and a video display 17. Preferably the video display has high resolution suitable for depicting graphical output and has screen dimensions within about 6 cm square.

Additional controls are shown in Figure 3.

The additional controls/functions shown in Figure 3 comprise external input 50, display brightness control 51, earpiece output (for stethoscope) 52, stethoscope on/off control 53, power on/off switch 54, external output to recorder/monitor 55, battery recharge contacts 56 and operational controls for the video display 17 comprising record button 57, calibrate 58, sweep button 59, freeze button 60 and reset button 61.

In use, the device is typically applied to the skin surface on the chest of a patient. Observing correct orientation, the user will be able to monitor ECG waveforms directly together with heart rate, respiration, temperature and heart and lung sounds. All parameters other than the heart and lung sounds can be output to the display unit 17. The heart and lung sounds can be directed to the speaker 16 or to an external audio output.

Information derived by the unit can be stored internally on a recording medium and/or output to external monitoring means.

Functions available include calibrate, sweep, freeze and record as typically found in storage display systems.

Power for the device is provided by external means or internal (rechargeable) batteries. The device will also accept audio or electrical input from a stethoscope. The device will also accept twelve lead ECG input for more sophisticated processing and display.

Optional external devices include temperature sensors, printer, battery charger, blood pressure sensor, recorders/computers and centralised patient monitoring systems.

Figure 4 shows a typical output on the video display 17 of the preferred embodiment. The display shows an ECG waveform 23 above which is displayed, digitally, heart beat rate 24 and body temperature 25. The user is thereby able to obtain, at a glance, in real time, a plurality of the patient's vital signs so that a quick and educated assessment of the patient's condition can be made on the spot. SECOND EMBODIMENT Referring to Figure 5 a second embodiment of the monitor unit 1 iis shown. Numbers on this figure correspond with like numbers on Figure 3 and identify the same components. The essential difference between the first and second embodiment resides in the electrode configuration of electrodes 11, 12 and 13. In the second embodiment a maximum distance between electrodes 11 and 12 is arranged within the constraints of the casing as shown.

Referring to Figure 6 the device of the second embodiment provides on the display 17, in real time, an ECG waveform 23 in analog form as well as heart rate 24, temperature 25 and respiration rate 26 in digital form.

Referring to Figure 7 a block diagram of the electronic componentry of the second embodiment is shown. The components comprising the diagram are microprocessor 30, EPROM 31, RAM 32, display controller 33, address decoder 34, power supply 35 and LCD display 36 components 30 - 33 are linked by a data-bus 37 and an address-bus 38. The microprocessor unit 30 receives both analog inputs comprising respiration, temperature and ECG and digital inputs from the control switches. A serial 1/0 link 39 is provided for printer or computer connection. The microprocessor 30 is, in fact, a Motorola MC 68HC11 microcontroller chip which incorporates analog to digital conversion on board together with other functions which, combined with low power requirements, is eminently suitable for use in a deviεe where compactness is important. The LCD display 36 is, in this embodiment, a 240 pixel by 220 pixel display driven at a sweep rate of 12.5 mm per second. This provides an effective screen bandwidth of around 50 Hz which, whilst below diagnostic quality, is sufficient for bedside use.

Data acquisition by the onboard analoged digital converter of the microprocessor 30 is around 200 samples per second thereby providing data acquisition at a diagnostic quality of approximately 100 Hz bandwidth. The screen, under normal operations, scrolls the acquired ECG waveform horizontally across the screen, holding approximately 3 seconds of waveform output on the 2 inch diagonal screen. The freeze button 60 (Figs. 3, 5) allows the waveform to be frozen if desired.

The RAM 32 comprises approximately 32 K of memory of which approximately 16 K is reserved for holding the digitally acquired ECG waveform. Under normal circumstances, therefore, the memory represents a moving buffer of approximately 80 seconds of ECG waveform. If the unit is used for longer than 80 seconds then information is overwritten on a first in, first out basis. The memory contents can be dumped to a printer/ personal computer by use of the serial I/O port 39. Preferably this port comprises an infrared link whereby information can be dumped whilst the monitor l is still in use at the bedside if desired. In an alternative mode the RAM 32, or at least a portion thereof, can be used for storing specific frozen frames.

Referring to Figure 8 some exemplary input circuits are provided suitable for use with either the first or second embodiments. These include a skin temperature sensor circuit which receives a signal from the thermistor 20 embedded in electrode 13, which signal is delivered to an amplifier 40 prior to supply to the microprocessor 30. The thermometer can be a type MB supplyed to Takara. Also shown is a microphone circuit deriving a signal from microphone 19 embedded in electrode 11, which signal is delivered to buffer amplifier 41, thence to band pass filter 42 and thence to the microprocessor unit 30 and, optionally, to a buffer amplifier circuit 43 which can drove earphones 440. The earphones, if used, effectively provide an electronic stethoscope.

The electrodes typically comprise stainless steel and, in this embodiment, comprises platinum plated stainless steel to prevent DC offset problems.

The thermistor 20 in electrode 13 must be electrically isolated and thermally insulated from the surrounding electrode structure in order to ensure a rapid and reliable response to body temperature changes. For oral or rectal temperature the thermistor is contained in a probe which connects to external input port 50.

The stethoscope assembly comprising the electret microphone 19 as shown in Fig. 8 is covered by a membrane 49 which, as is usual in prior art stethoscopes, defines an acoustic chamber between the skin contacting membrane and the receiving horn of microphone 19.

Also shown in Figure 8 is a buffer input circuit for the ECG signals. The three electrodes 11, 12 and 13 provide an "ECG 1" positive from electrode 11, "ECG 2" from negative electrode 13 and reference signal to the input of the buffer circuit. The buffer circuit itself comprises a 400 MHz constant current source 44, instrumentation amplifier 45 feeding a bandpass filter 46 and final buffer amplifier 47 prior to delivery to the microprocessor unit 30. An RMS voltage detector 48 provides a direct RMS signal of the ECg waveform to the microprocessor unit 30. Flgures 9, 10 and 11 show logic flow diagrams for software for the programming of the microprocessor unit 30. Specifically figure 9 shows ECG and heart rate display driver software logic. Figure 10 shows respiration display software driver logic. Figure 11 shows the temperature display software logic. This software is contained in EPROM 31 together with other software for controlling the microprocessor unit 39.

Concerning respiration measurement specifically electrode ECG 1 (electrode 11) is used to inject a 400 KHz sinusoidal current of approximately 1 mA into the body. Variations in body impedance due to changes in oxygen content will appear as voltage fluctuations on the reference electrode. The RMS voltage detector 48 provides a RMS reading of this fluctuation to the microprocessor unit 30. Utilising the software as outlined in Fig. 10 the respiration (breathing) rate of the patient can be output to the display - item 26 in Fig. 6.

In use the device of the second embodiment functions similarly to that of the description of the first preferred embodiment. Additionally, as shown in figure 6, a respiration rate read out 26 is also provided.

The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope and spirit of the present invention.

In particular it should be noted that alternative electrode configurations can be used. It 1s Important only that the configurations and orientation of the monitor unit 1 are such that ECG waveforms displayed are displayed in an orientation which is "standard" as known in the art.

Claims (7)

1. A portable, self-contained, physiological monitor, said monitor including multifunctional electrodes arranged in a planar configuration on a first surface of said monitor, said monitor further including data processing means to receive and analyse signals received from said multifunctional electrodes, said monitor further including output means to output information analysed by said data processing means to a user, said monitor adapted to sense and display a plurality of vital signs at the same time in real time.

2. The monitor of claim 1 wherein said multifunctional electrodes comprise first, second and third electrodes arranged in planar, triangular configuration.

3. The monitor of claim 2 wherein said first electrode includes a sound sensor and said second electrode includes a thermal sensor.

4. The monitor of claims 2 or 3 wherein all sides of said planar, triangular configuration are less than 10 cm.

5. The monitor of any one of claims 2, 3, or 4 wherein said electrodes at a skin contacting surface have a diameter in the range 1.5 cm to 3.5 cm.

6. The monitor of any preceding claim wherein said output means includes a video display adapted to display ECG waveforms and digital data.

7. A method of monitoring the vital signs of a living human being comprising applying a portable physiological monitor to a chest region of a patient, said monitor comprising a portable, selfcontained, physiological monitor said monitor including multifunctional electrodes arranged in a planar configuration on a first surface of said monitor, said monitor further including data processing means to receive and analyse signals received from said multifunctional electrodes, said monitor further including output means to output information analysed by said data processing means to a user, said monitor adapted to sense and display a plurality of vital signs at the same time in real time.