REMOTE SENSING BLOOD MONITORING SYSTEMThe present invention relates to oximeters, and particularly concerns medical or veterinary oximeters which can measure blood oxygen content and pulse rate without causing trauma or discomfort to a patient. Such oximeters can be used in human or veterinary medicine for monitoring a patient's or an animal's pulse and blood oxygen, for example during a medical or veterinary operation.
Conventional pulse oximeter probes are constructed for medical use by providing a spring clamp which engages the patient's finger end, a source of light and a light detector being pressed against the finger by the spring.
Light emitted by the source passes through the patient's finger, and the pulsation of blood in the patient's blood vessels causes the amount of light transmitted to vary in synchronism with the pulse. By detecting the amount of light transmitted and measuring the variation with time, the patient's pulse rate can be calculated.
Conventionally constructed probes, as well as being difficult to clean due to their multi-component construction, have the disadvantage that they are susceptible to interference from external light sources, and for example in outdoor conditions of bright sunlight the detector is unable to discriminate between ambient light and light from the light source, thus preventing any calculation of pulse rate or blood oxygenation. In addition, the attachment of the clamp-type probe to a finger causes inconvenience, and can impede the activities of the patient.
The present invention seeks to provide a blood monitoring system, and preferably a pulse oximeter, which can be used in veterinary medicine to monitor an animal's blood parameters over a long period while the animal is unrestrained, and can also be used in human medicine for monitoring a person's blood parameters while they continue their activities. In particular, the oximeter is intended for use by fire-fighters, divers, or others working in hazardous environments and particularly where breathing apparatus is used, so that the blood parameters of the person can be monitored in real time.
A further objective is to provide an oximeter which can be used not only to measure blood oxygen levels, but can simultaneously monitor carbon monoxide levels in the blood.
The present invention thus seeks to provide a blood monitor, preferably an oximeter, having a probe which can be applied to a patient, and left in place to provide a signal to a remote monitoring station without inconvenience to the patient. The probe is to be usable in all ambient light conditions, and must be simple to use and easy to clean between uses.
According to a first aspect of the present invention, a remote sensing blood monitoring system includes a probe having a body arranged to support a light source for emitting light of a predetermined wavelength and a detector for detecting light emitted by the light source, the light source and detector being positioned, in use, adjacent a patient's skin so that light from the light source can traverse a patient's tissue and enter the detector to produce an output signal, processing circuitry to process the output signal from the detector to determine a first parameter relating to patient's blood from the output signal, and further includes signalling means to transmit a signal corresponding to the patient's blood parameter to a remote receiving station, and display means to display an indication of the patient's blood parameter at the remote receiving station.
In a preferred embodiment, the blood monitor is an oximeter and the system includes a probe having a light detector, a first light source emitting light of a first predetermined wavelength and a second light source emitting light of a second predetermined wavelength, the probe having a body arranged to support the light sources and detector adjacent a patient's skin so that light from the sources can traverse a patient's tissue and enter the detector to produce first and second respective output signals, processing circuitry to calculate the blood oxygen level from the output signals, and signalling means to transmit a signal corresponding to the patient's blood oxygen level to a remote receiving station which includes a display means.
Most preferably, the instrument functions as a pulse oximeter in the conventional way by detecting the amount of light transmitted through the patient's tissue and processing the signal to detect the frequency of the synchronous variation of the amount of transmitted light with the pulse.
By further processing the received signal, using light of two predetermined wavelengths on opposite sides of the isoblastic point (a wavelength of approximately 800nm), the amount of light of each wavelength which is absorbed during its passage through the patient's tissue can be detected and processed to calculate the amount of oxygen in the blood.
The probe body may advantageously also support a third light source emitting light of a third wavelength so that light from the third source can also traverse the patient's tissue and enter the same or a different detector, and the processing circuitry may be arranged so as to be able to calculate the blood carbon monoxide level from the output signals received from the detector, to display on the display means an indication of the patient's blood carbon monoxide level. Preferably the the third wavelength is from 860 to 1000nm.
The signal transmitted by the signalling means to the remote receiving station may be the output signal from the detector or detectors, or may be the processed output signal from the processing circuitry. In the former case the processing circuitry will be located at the remote receiving station, and in the latter case the processing circuitry will be located on the wearer, and a second display may be provided for the wearer to check his own blood parameters if desired.
The signal may be transmitted by any suitable means including radio, infra-red or ultrasound signalling methods.
In an advantageous embodiment, the processing circuitry may include a comparator which compares the patient's blood parameters with predetermined limits or ranges, and the display may include coloured light signals, and/or warning tones may be emitted, when preset limits are exceeded or when the measured value of a parameter is outside its corresponding preset range.
The probe is preferably shielded from the effects of ambient light by making the body of the oximeter probe opaque to light of the predetermined wavelengths, and the body is preferably opaque to all visible light.
The receiving station has a display means, and preferably also a recording means to provide a record of the pulse and blood oxygen level over a period of time. The display means is preferably an alphanumeric display such as an LED display, and may include indicators to show when safe values are exceeded, or when measured parameters lie in safe ranges. The recording means may be a memory device associated with the processing circuitry to which parameter values are written at discrete intervals, or may be an analogue recorder such as a paper sheet or roll on which a printing device records the parameter value continuously.
In an advantageous embodiment of the invention, there is provided a remote blood monitoring system comprising a probe mounted in a facepiece of a breathing apparatus at a position corresponding to an artery of the wearer, the probe having a light detector, a first light source emitting light of a first wavelength, control circuitry to cause light to be emitted by the light source and detected by the detector, processing means associated with the detector output to calculate a value of a blood parameter of the wearer, and signalling means to transmit a signal corresponding to the output from the detector to a remote receiving station having a display.
The probe mounted in the facepiece may further comprise a second light source emitting light of a second wavelength so that light from the second source can also traverse the patient's tissue and enter the detector, and the processing circuitry may be arranged so as to be able to calculate and display the blood oxygen level from the output signals received from the detector.
Most preferably the probe of the blood monitoring system has a first light source emitting light with a spectrum including a first wavelength susceptible to absorption by oxygenated blood, a second light source emitting light with a spectrum including a second wavelength susceptible to absorption by deoxygenated blood, and a third light source emitting light with a spectrum including a third wavelength susceptible to absorption by blood contaminated with carbon monoxide. In an advantageous embodiment, the light sources emit light in sequential timed pulses which are detected by the same detector, and the processing circuitry divides the detector output to separate the signal into signal portions relating to the detection of the different light wavelengths.
Facepieces fitted with probes having a single light source and detector are also contemplated, but in this case the probe output signal processing circuitry may only process the probe output signal to determine the wearer's pulse rate.
Embodiments of the invention will now be described in details with reference to the accompanying drawings, in which: Figure la is a sectional side view of a first surface mounted probe;Figure ib is a sectional side view of an alternative surface mounted probe; andFigure 2 is a schematic diagram of a probe placed in a facepiece of a breathing apparatus.
Referring now to Figures la and ib, the probe 1 comprises a planar body of resilient material, with sensor components mounted inside the body of the probe 1.
The body is made of a resilient, flexible, waterproof material, such as natural or synthetic rubber, and is preferably circular or elliptical in plan view. The material of the probe is preferably opaque a preferred colour being white, but may be transparent or translucent.
Figure la shows a central section along the main body 1, with a light source 2 and a detector or receiver 3 mounted within the body 1 below a window 4. The window 4 is made of an optically clear material, preferably silicone rubber, the material being equally inert and having a flexibility similar to the body of the probe 1.
The electrical components 2 and 3 are thus completely encapsulated, Electrical connections are made by wires 5 passing through the body 1 of the probe and exiting the probe at one of its ends.
The light source 2 is preferably a light emitting diode having a known emission wavelength. The light emitted is preferably red and/or infra-red with a spectrum including wavelengths between about 600 and 700 nm, most preferably about 660nm.
The preferred method of producing the probe is to place the light source 2, detector 3, window 4 and leads 5 in a mould cavity and injection mould the body 1 to embed the other components therein.
In an alternative advantageous embodiment, not illustrated, the light source and detector are positioned beneath separate transparent windows, and a partition of opaque body material between the windows prevents light from the light source passing directly to the detector.
Figure lb shows the cross section of a second probe, in which separate windows 14 are formed to cover first and second light sources 2a and 2b, and detector 3, respectively. A neoprene layer 17 and an opaque filler 18 make up the rest of the sandwich construction of this probe.
The light sources 2a and 2b and the receiver 3 are positioned such that light passes through the windows 14 which have been formed in the body of the probe 1, which may either be cast using the same inert materials as previously described, or may be produced using a sandwich technique with neoprene rubber or closed cell Plastizote.
By utilising a light source 2a having a spectrum including a first wavelength of from 600 to 700 nm, predominantly responsive to deoxygenated blood, and a second light source 2b having a second wavelength of from 900 to 980 nm, preferably about 940 nm, predominantly responsive to oxygenated blood, the monitor will be able to distinguish carboxyhaemoglobin from oxyhaemoglobin.
This will enable the oximeter to give meaningful data in the event of smoke inhalation or carbon monoxide poisoning.
The light sources 2a and 2b may be positioned equal distances either side of the receiver 3, but asymmetric arrangements may be preferred in some situations.
it is envisaged that the light sources of the probe will be controlled by control circuitry to emit light in pulses, for example by emitting a pulse from light source 2a followed by a period of darkness, then a pulse from light source 2b followed by a second period of darkness, and finally simultaneous pulses from both light sources followed by a third period of darkness. This cycle could then be repeated, with the greater magnitude of signal from the combined pulse serving to mark the receiver output, enabling the individual pulses to be identified as being either the first or second pulse following the combined pulse. When three light sources are used, sequential pulsing of the sources followed by simultaneous pulsing of two or three sources together enables the processing circuitry to distinguish the detector readings for each source.
Detection circuitry in association with the detector 3 will then analyse the signals from the detector 3, to detect the overall signal strength and thus calculate pulse rate, and also to analyse the absorption ratios for the respective wavelengths, associated with levels of oxygen and of carbon monoxide in the blood.
Figure 2 shows the probe 1 attached to the sealing flange 10 of a facepiece 11 of a breathing apparatus 12. The probe 1 is positioned close to the centreline of the facepiece, above the visor 13 in the embodiment shown, so as to be applied to the forehead of the wearer over a superficial artery such as the supraorbital artery.
Alternatively, the probe 1 may be positioned at the side of the visor to be applied for example to the anterior temporal artery on the scalp. Clearly, the probe may be of the type shown in Figure la, and may measure only blood oxygen. Alternatively the probe may be of the type shown in Figure lb, and may be removably attached to the facepiece, and a plurality of mounting sites may be provided on the facepiece so that each individual wearer can choose the site which gives the strongest output signals from the detector.
It should be noted that if the filler is made of clear silicon rubber, then the clear cover 16 is not required.
Also, by exaggerating the area of the flange of layer 16 to extend outwards well beyond the windows 14, the probe lends itself to attachment to animals using adhesive, for example an adhesive such as super glue.