GB2448323A

GB2448323A - Respiratory Rate Measuring Apparatus

Info

Publication number: GB2448323A
Application number: GB0706881A
Authority: GB
Inventors: Mark Sinclair Varney
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-10
Filing date: 2007-04-10
Publication date: 2008-10-15
Also published as: GB0706881D0

Abstract

An apparatus is provided for measuring the respiratory rate of a subject (adult, child, animal or other living / breathing subject), including; a sensor that determines the exhaled water vapour concentration; a calculating device for iteratively calculating properties of individual breath; a method for outputting the respiratory rate based on evaluation of the values produced by the device. The device may optionally transmit an alarm to a remote receiver when respiratory irregularities are detected. Claims are also included for a sensor for detecting water vapour in a gas stream which comprises a first electrode; a second electrode; an active substrate extending between the first and second electrodes, the active substrate being selective to water vapour, such that the presence of water vapour varies the electrical conductivity of the path between the first and second electrodes. The sensor is suitable for analyzing the water vapour content of breath exhaled by a subject in the assessment of respiratory rate and / or respiratory function. The sensor is enclosed within a housing such that the exhalation is unaffected, causing no back-pressure to the breath or increase in exhalation effort, thereby allowing normal tidal breathing.

Description

Aeld of Invention: The present invention generally relates to sensing

of respiratory rate, respiration monitoring and respiration monitoring equipment. More particularly, tls invention relates to a novel method and sensor for detecting exhaled breath by the analysis of water vapour. Such device may be used to detect and monitor common respiratory and potentially life-threatening respiratory events. The equipment may be used with humans and animals, extending also for use for patients in hospitals, ambulances and other paramedic situations.

Background:

Respiratory rate Is one of the most important physiological parameters reflecting the spontaneous living status of asubject. It Is a vital component of most medical and nursing records, and is used in many clinical scoring systems. Extremes of respiratory rate usually Indicate the need for urgent medical Intervention. Typically, the measurement of respiratory rate is based on human observation.

It is known in the art to monitor patients susceptible to disorders of the respiratory system, or in critical care environments to employ respiratory sensors and alarm systems. In general, a change in an individual's respiration (known as "apnea" when such a change is a transient cessation of respiration) corresponds to a change in the physical condition of that individual. In the case of individuals with obstructive sleep apnea, a change in respiration may be attributable to present or impending physical distress. Accordingly, there is a need for a simple and reliable method of sensing respiration, and changes in respiration, that will meet medical and clinical needs for monitoring individuals at risk of respiratory distress. There is an especial need to monitor new-born infants.

There have been a multitude of airflow sensors employed to measure the volume and rate of breathing. These are variously based on physical measurements (light, sound, pressure, air velocity, etc.) and chemical measurements (gas sensing, temperature, infrared light absorption, etc.) For example, EP0484174 describes a complex assembly.

For example, U5531 1875 and US7089932 describe the use of polyvinyliderie fluoride (PVDF) as suitable transducer films for sensing the temperature difference between inspired and expired breaths.

Other possible solutions include spectroscopic (infrared) end-tidal CO2 monitors, catheterization, and (simple) visual observation. Such measurements are either invasive' (and cause e.g. back-pressure and therefore change the subjects' breathing), and/or are expensive/complicated to implement into a handheld, battery-operated instrument, and/or are subject to component failure for one reason or another.

Thus there is a need in the field of medical healthcare for a simple, inexpensive, battery-operated, robust sensor for the non-invasive measurement of respiratory rate, and which does not require artificial sources of radiation or complex equipment. A basic object of the present invention is the provision of improved respiratory monitoring equipment.

The fundamental concepts of this invention will be widely applicable to many medical and non-medical applications.

Description:

The present invention overcomes the disadvantages found in the prior art by providing a respiratory rate measurement, derived from the measurement of exhaled water vapour, via an etectrochemical sensor mounted within the airstream of a living subject. (It is assumed herein that the terms "respiration rate" and "respiratory rate" are synonymous. It is also assumed herein that respiratory rate is defined as the number of breaths per minute (bpm).} Moreover, the present invention includes a sensor construction which is less susceptible to interference from the external environment, patient motion, and loss of signal.

Breathing may be wholly nasal, wholly oral, or a combination of both -and with changes between the various modes (particularly during sleep). A problem for workers in the field is ensuring that the breath always impinges upon the sensor, to avoid any false reading. The sensor may be incorporated within a breathing tube, a cannula, mask or other apparatus formed on or around the face (Figure 1).

Preferably, the sensor is mounted within a standard 20mm id tubing adaptor, such that it can be easily mounted within a mask or fitted into commercially-available breathing lines and tubing.

Whilst the use of a face mask channels respiratory flow to the sensor, a face mask may be unsuitable for some patients and/or animals in which case the arrangement in Figure 2 could provide a less intrusive solution. The sensor may also be adapted so that it can be placed adjacent to the nostrils, perhaps taped to the upper lip and oriented so that the sensor is directly underneath a nostril.

The sensor may optionally be wirelessly connected to a suitable signal recording and display unit (Figure 3).

The sensor may also be mounted within standard gas delivery lines such as oxygen (Figure 4).

The respiratory sensor monitors the extent of breathing by measuring the changes in humidity, as a function of tidal volume and/or time.

According to the present invention there is provided, in a first aspect, a sensor for detecting a target component in a gas stream, the sensor comprising: o afirstelectrode; o a second electrode; o an active substrate extending between the first and second electrodes, the active coating being selective to water vapour, such that the exhalation of water vapour varies the electrical conductivity of the path between the first and second electrodes.

The coating, by being selective in its activity to water vapour, provides the sensor with the ability to measure the quantity of water vapour in the gas stream being analysed or monitored. It follows that two or more similar sensors may be combined, each having a coating with a different activity, in order to increase the confidence of water vapour detection.

In a preferred embodiment, the coating is active with respect to water vapour, such that the conductance of the electrical path established between the electrodes is proportional to the concentration of water vapour in the gas stream.

Suitable materials for the coating include Zeolites and silicalites. Suitable Zeolites include the naturally occurring and synthetic Zeolites. The methods of preparing suitable Zeolites are well known in the art and suitable Zeolites for use in the sensor of the present invention are available commercially.

The active coating is preferably porous, with Zeolites being a particularly preferred porous material.

Zeolites, being highly porous materials belonging to the class of aluminosilicates have been found to be particularly suitable for use as or comprised in the active coating of the sensor of the present Invention. Zeolites are characterized by having a crystalline structure with a 3-dimensional pore system. The pores are precisely defined in terms of their diameter. The diameter of the pores may be controlled by subjecting the Zeolite to ion-exchange with appropriate cations, using techniques well known in the art It has been found that the speed of response of the sensor is, in part, dependant upon the relationship of the pore size of the active coating material with the diameter of the target species or molecule in the gas stream being analysed. In particular, it has been found that active coating materials, especially Zeolites, having pores with a diameter significantly greater than that of the target molecule give rise to a sluggish or slow response of the sensor to changes in the composition of the gas stream being analysed. In contrast, the speed of response of the sensor increases as the pore diameter approaches the diameter of the target molecule. Accordingly, it is preferred that the diameter of the pores of the active coating material are not substantially greater than the diameter of the target species or molecule. More preferably, the nature of the coating material can be chosen by experiment, choosing that which has the fastest speed of response.

Suitable Zeolites for use in the sensor of the present invention include the Type A, Type P and Type X Zeolites. Preferred Zeolites include Zeolite 4A and 13X. Zeolite 4A, having a pore diameter of about 4 Angstroms, is a particularly preferred Zeolite for use when the target molecule in the gas stream is water vapour, the measurement of which is particularly important in the analysis of respiratory disorders in humans and animals, as discussed hereinafter.

Suitable Zeolites for use in the sensor of the present invention are known in the art and available commercially, or may be prepared using techniques and methods well known in the art.

Synthetic aluminium-magnesium hydroxycarbonates, in particular hydrotalcite, are also suitable for use as the active substrate material.

The sensor is particularly suitable for the detection of water vapour present in the exhaled breath of a person, or animal. In addition, the sensor provides a fast and accurate response to changes in the water vapour content of the gas stream being analysed. These features make the sensor of the present invention particularly suitable for use as a respiratory rate sensor in the analysis of exhaled breath of a subject.

The present invention provides a sensor that is particularly compact and of very simple construction. In addition, the sensor may be used at ambient temperature conditions, without the need for any heating or cooling, while at the same time producing an accurate measurement of water vapour concentration in the gas being analysed.

The sensor comprises a first or working electrode and a second or counter electrode. Such a two-electrode construction is known in the art. The electrodes may comprise any suitable metal or alloy of metals, with the proviso that the electrode does not react with the electrolyte or any of the substances present in the gas stream. Preference is given to metals in Group VIII of the Periodic Table of the Elements (as provided in the Handbook of Chemistry and Physics, 62nd edition, 1981 to 1982, Chemical Rubber Company). Other suitable metals include copper, silver and gold. Preferably, each electrode is prepared from gold or platinum. Carbon or carbon-containing matersal5 may also be used to form the electrodes.

The electrodes may have any suitable shape and configuration. Suitable forms of electrode include points, lines, rings and flat planar surfaces. The effectiveness of the sensor can depend upon the particular arrangement of the electrodes and may be enhanced in certain embodiments by having a very small path length between the adjacent electrodes. This may be achieved, for example, by having each of the first and second electrodes comprise a plurality of electrode portions arranged in the form of an array of interdigitated electrode portions, in particular arranged in a concentric or rectangular pattern.

The electrodes are preferably oriented as close as possible to each other, to within the resolution of the manufacturing technology. The first and second electrode can be between 10 to 1000 microns in width, preferably from 50 to 500 microns. The gap between the first and second electrodes can be between 20 and 1000 microns, more preferably from 50 to 500 microns. The optimum track-gap distances are found by routine experiment for the particular electrode material, geometry, configuration, and substrate under consideration. In a preferred embodiment the optimum first (or working) electrode track widths are from 50 to 250 microns, preferably about 100 microns, and the second (or counter) electrode track widths are from 50 to 750 microns, preferably about 500 microns. The gaps between the first and second electrodes are preferably about 100 microns.

The first electrode and second electrode may be of equal size. However, in one preferred embodiment, the surface area of the second or counter electrode is greater than that of the first or working electrode to avoid restriction of the current transfer. Preferably, the counter electrode has a surface area at least twice that of the working electrode. Higher ratios of the surface area of the counter electrode and working electrode, such as at least 3:1, preferably at least 5.1 and up to 10:1 may also be employed. The thickness of the electrodes is determined by the manufacturing technology, but has no direct influence on the electrochemistry. The magnitude of the resultant electrochemical signal is determined principally by exposed surface area, that is the surface area of the electrodes directly exposed to and in contact with the gaseous stream. Generally, an increase in the surface area of the electrodes will result in a higher signal, but may also result in increased susceptibility to noise and electrical interference. However, the signals from smaller electrodes may be more difficult to detect.

In its simplest form, the sensor consists of the electrodes in combination with the active coating. For example, the electrodes may be applied to the surface of the coating material or encapsulated within or underneath the coating material.

In a preferred embodiment, the sensor comprises an inert support, upon which is deposited the active coating. The inert substrate may be any suitable material, with the proviso that it does not react or interact with the coating, the electrodes or the components in the gas stream to be analysed. Suitable inert substrates include glass, polymers, ceramics and the like. The use of an inert substrate offers the advantage of providing strength and rigidity to the sensor assembly. In addition, the inert substrate allows the thickness of the active coating to be reduced and the path length of the gas components entering the coating and the conductive path between the electrodes to be more closely controlled. This in turn provides for a sensor that is robust, more accurate and more responsive.

In one arrangement, the active coating is deposited on top of the electrodes applied to the substrate layer. An alternative arrangement is to have at least one of the electrodes applied directly to the surface of the inert substrate and the active coating applied as a layer over both the electrode and substrate. In this way at least one or both of the electrodes is disposed between the coating and the inert substrate.

To improve the electrical insulation of the electrodes, the portions of the electrodes that are not disposed to be in contact with the gaseous stream (that is the non-operational portions of the electrodes) may be coated with a dielectric material, patterned in such a way as to leave exposed the active portions of the electrodes.

While the sensor operates welt with two electrodes, as hereinbefore described, arrangements with more than two electrodes, for example including a third (or reference) electrode, as is well known in the art. The use of a reference electrode provides for better potentiostatic control of the applied voltage, or the galvanostatic control of current, when the "jR drop" between the counter and working electrodes is substantial. Dual 2-electrode and 3-electrode cells may also be employed.

A further electrode, disposed between the counter and working etectrodes, may also be employed.

The temperature of the gas stream may be calculated by measuring the end-to-end resistance of the electrode. Such techniques are known in the art.

The electrodes of the sensor of the present invention may be formed by printing the electrode material in the form of a thick film screen printing ink onto the substrate. The ink consists of four components, namely the functional component, a binder, a vehicle and one or more modifiers. In the case of the present invention, the functional component forms the conductive component of the electrode and comprises a fine powder of one or more of the aforementioned metals used to form the electrode.

The binder holds the ink together on the substrate and merges with the substrate during high temperature firing. The vehicle acts as the carrier for the powders and comprises both volatile components, such as solvents, and non-volatile components, such as polymers. Both the binder and vehicle materials evaporate during the early stages of drying and firing respectively. The modifiers comprise small amounts of additives, which are active in controlling the behaviour of the inks before and after processing.

Screen printing requires the ink viscosity to be controlled within limits determined by rheological properties, such as the amount of vehicle components and powders in the ink, as well as aspects of the environment, such as ambient temperature.

The printing screen may be prepared by stretching stainless steel wire mesh cloth across the screen frame, while maintaining high tension. An emulsion is then spread over the entire mesh, filling all open areas of the mesh. A common practice is to add an excess of the emulsion to the mesh. The area to be screen printed is then patterned on the screen using the desired electrode design template.

The squeegee is used to spread the ink over the screen. The shearing action of the squeegee results in a reduction in the viscosity of the ink, allowing the ink to pass through the patterned areas onto the substrate. The screen peels away as the squeegee passes. The ink viscosity recovers to its original state and results in a well defined print. The screen mesh is critical when determining the desired thick film print thickness, and hence the thickness of the completed electrodes.

The mechanical limit to downward travel of the squeegee (downstop) should be set to allow the limit of print stroke to be 75 -l2Siim below the substrate surface. This will allow a consistent print thickness to be achieved across the substrate whilst simultaneously protecting the screen mesh from distortion and possible plastic deformation due to excessive pressure.

To determine the print thickness the following equation can be used: T = (Tm X A0) + Where: T = Wet thickness (i.tm); Tm = mesh weave thickness (pm); A0 = % open area; Te = Emulsion thickness (tim).

After the printing process the sensor element needs to be levelled before firing. The levelling permits mesh marks to fill and some of the more volatile solvents to evaporate slowly at room temperature. If all of the solvent is not removed in this drying process, the remaining amount may cause problems in the firing process by polluting the atmosphere surrounding the sensor element.

Most of the solvents used in thick film technology can be completely removed in an oven at 150 C when held there for 10 minutes.

Firing is typically accomplished in a conveyor belt furnace. Firing temperatures vary according to the metal powder and ink chemistry. Most commercially available systems fire at 850 C peak for 10 minutes. Total furnace time is 30 to 45 minutes, including the time taken to heat the furnace and cool to room temperature. Purity of the firing atmosphere is critical to successful processing. The air should be cJean of particulates, hydrocarbons, halogen-containing vapours and water vapour.

Alternative techniques for preparing the electrodes and applying them to the substrate or inert support, if present, include spin/sputter coating and visible/ultraviolet/laser photolithography. In order to avoid impurities being present in the electrodes, which may alter the electrochemical performance of the sensor, the electrodes may be prepared by electrochemical plating ("electroplating"). In particular, each electrode may be comprised of a plurality of layers applied by different techniques, with the lower layers prepared using one of the aforementioned techniques, such as screen-printing, and the uppermost or outer layer or layers being applied by electrochemical plating using a pure metal salt, such as gold chloride for the electroplating of gold metal.

In a further aspect, the present invention provides a method of detecting water vapour in a gas stream, the method comprising: * contacting the gas stream with an active substrate extending between first and second electrodes; * determining the variation in the electrical conductivity of the path between the first and second electrodes; and * providing an indication of the presence of water vapour in the gas stream.

The variation in the electrical conductivity of the coating may be determined by applying a voltage to the first and second electrodes. The voltage may be applied in a Continuous (dc) manner or in an ac, intermittent or pulsed form. The voltage, when applied, may be a constant voltage or may cycle between a lower (rest) voltage and a higher voltage.

The method requires that an electric potential is applied across the electrodes and conductivity estimated by the measurement of current passing between the electrodes. In one simple configuration, a voltage is applied to the counter electrode, while the working electrode is connected to earth (grounded). In its simplest form, the method applies a single, constant potential difference across the working and counter electrodes. Alternatively, the potential difference may be varied against time, for example being pulsed or swept between a series of potentials. In one embodiment, the electric potential is pulsed between a so-cafled rest' potential, at which no reaction occurs, and a reaction potential.

In operation, a linear potential scan, sinusoidal waveforms, multiple voltage steps or one discrete potential pulse are applied to the working electrode, and the resultant Faradaic reduction current is monitored as a direct function of the dissolution of water molecules in the coating bridging the electrodes.

The current that passes between the counter and working electrodes is converted to a voltage using a resistor, R, and recorded as a function of the water vapour concentration in the gaseous stream.

The measured current in the sensor element is usually small. As a result of the small current flow, careful attention to electronic design and detail may be necessary. In particular, special "guarding" techniques may be employed. Ground loops need to be avoided in the system. This can be achieved using techniques known in the art. The sensor responds faster by pulsing the potential between two voltages, a technique known in the art as Square Wave Voltammetry'. Measuring the response several times during a pulse may also be used to assess the impedance of the sensor.

The shape of the transient response can be simply related to the electrical characteristics (impedance) of the sensor in terms of simple electronic resistance and capacitance elements. By careful analysis of the shape, the individual contributions of resistance and capacitance may be calculated. Such mathematical techniques are well known in the art. Capacitance is an unwanted noisy component resulting from electronic artefacts, such as charging, etc. The capacitive signal can be reduced by selection of the design and layout of the electrodes in the sensor. Increasing the surface area of the electrodes and increasing the distance between the electrodes are two major parameters that affect the resultant capacitance. The desired Faradaic signal resulting from the passage of current due to reaction between the electrodes may be optimized, by experiment.

Measurement of the response at increasing periods within the pulse is one technique that can preferentially select between the capacitive and Faradaic components, for instance. Such practical techniques are well known in the art.

The potential difference applied to the electrodes of the sensor element may be alternately or be periodically pulsed between a rest potential and a reaction potential, as noted above Figure 8 shows examples of voltage waveforms that may be applied. Figure 8a is a representation of a pulsed voltage signal, alternating between a rest potential, V0, and a reaction potential VR. The voltage may be pulsed at a range of frequencies, typically from sub-Hertz frequencies, that is from 0.1 Hz, up to 10kHz. A preferred pulse frequency is in the range of from 1 to 500 Hz. Alternatively, the potential waveform applied to the counter electrode may consist of a "swept" series of frequencies, represented in Figure 8b. A further alternative waveform shown in Figure 8c is a so-called "white noise" set of frequencies. The complex frequency response obtained from such a waveform will have to be deconvoluted after signal acquisition using techniques such as Fourier Transform analysis.

Again, such techniques are known in the art.

One preferred voltage regime is OV ("rest" potential), 2SOmV ("reaction" potential), at a 20Hz pulse frequency.

It is an advantage of the present invention that the electrochemical reaction potential is approximately +0.2 volts, which avoids many (if not all) of the possible competing reactions that would interfere with the measurements, such as the reduction of other metal ions (such as copper ions) and atmospheric oxygen.

The method of the present invention is particularly suitable for use in the analysis of the exhaled breath of a person or animal. From the results of this analysis, an indication of the respiratory condition of the patient may be obtained.

In a further aspect, the present invention provides a method of analyzing the exhaled breath of a person or animal, the method comprising: * causing the exhaled breath to contact an active substrate extending between first and second electrodes; * determining the variation in the electrical conductivity of the path between the first and second electrodes; - * providing an indication of the water vapour content of the exhaled breath, and; l0 * providing an indication of the respiratory rate of breathing The sensor arid method of the present invention are of use in monitoring and determining the respiratory rate of breathing of a patient or an animal. The method and sensor are particularly suitable for analyzing tidal concentrations of water vapour, in the exhaled breath of a person or animal, to diagnose or monitor a variety of respiratory conditions. The sensor is particularly useful for applications requiring fast response times, for example personal respiratory monitoring of patients undergoing surgery. Water vapour measurements can be applied generally in the field of respiratory medicine, airway diseases, both restrictive and obstructive, airway tract disease management, and airway inflammation. The present invention finds particular application in the field of monitoring and management of airway diseases (such as asthma and COPD). In particular, due to the versatility of the method and speed of response that may be achieved using the sensor and method of the present invention, the results may be used to provide an early alert to the onset of respiratory disease or illness.

Preferably, the respiratory rate sensor and apparatus are easily fabricated from low-cost materials and are adaptable for use in various medical environments, and for the monitoring of various medical conditions. The respiratory rate sensor and apparatus is particularly suitable for use in hospital and primary healthcare, especially for critical care patients.

It should be understood that the examples and embodiments described herein are illustrative only arid that variations or modification or changes thereof will be suggested to persons skilled in the art, and are to be included within the spirit and purview of this application and the scope of the appended claims.

II

Drawings Embodiments of the present invention will be described, by way of example only, having reference to the accompanying drawings, in which: Figure 1. A perspective schematic view of a typical embodiment of the invention, showing the sensor placed within a face mask attached to a patients' face and connected to a suitable device to display the respiration rate.

Figure2. A perspectiveschematic view ofatypical embodiment of the invention, showingthesensor placed directly onto to the upper lip of a patients' face and connected to a suitable device to display the respiration rate. Figure 3. A perspective schematic view of a typical embodiment of the

invention, showing the sensor placed within a face mask attached to a patients' face and connected to a suitable device to display the respiration rate Figure 4. A schematic representation of the sensor adapted for use within a standard oxygen delivery gas line, worn over a patient's head. The sensor is positioned in such a way to respond to air from the nostrils (nasal breathing) and to air from the mouth (mouth breathing).

Figures. An exploded isometric sectional view of a sensor according to a first embodiment of the present invention, showing the substrate, electrodes, dielectric and coating layers.

Figure 6. An isometric schematic view of an alternative embodiment of the sensor element according to the present invention.

Figure 7.

Figures 8a, 8b and 8c are voltage versus time representations of possible voltage waveforms that may be applied to the electrodes in the method of the present invention, as discussed hereinbefore.

Figure 9. A flow-diagram providing an overview of the inter-connection of sensor elements and their connection into a suitable measuring instrument of an embodiment of the present invention.

Figure 10. Graphical representations of the response of a sensor of the present invention to changes in the water vapour composition of exhaled breath.

Figure 11. A schematic representation of the electronic components between the sensor and a display unit, comprising a wired (or wireless) communication link.

Figure 12. A schematic representation of a display unit, showing a digital output of respiratory rate and an alarm indicator

Claims

What is claimed is: A respiratory rate sensor and apparatus, comprising: * A sensor sensitive to water vapour, capable of recording water vapour concentration at a frequency of at least 50Hz, disposable between the mouth and nose of a patient and adapted to be impinged by the patient's (or animal's) inspired and expired breaths * A method of connecting the sensor to a microcontroller, that controls the sensor and acquires measurements, which may be (wired or wirelessly) connected to a monitor and/or form of display.

* A mathematical approach that conditions the signal, performs signal averaging, shaping, and autocorrelation to simplify the signature of a breath as measured by this invention.

* A method of calculation that detects and computes respiratory rate by detecting and interpreting the variations in water vapour content as a function of tidal breathing.

* A monitor, connected to said controller, that collects, stores and displays the respiratory rate signals, and which is capable of onward transmission of such information * A monitor, including means of interpreting respiratory rate and activating an alarm in the event of detecting zero signal, or abnormal variation in signal according to predetermined limits.
2 A respiration rate sensor, according to claim 1, where the sensor is adapted for use within a face mask adapted to cover a patient's nostrils and mouth.
3 A respiration rate sensor, according to claim 1, where the sensor is adapted for use within an airline connected in some way to the patient airway.
4 A respiration rate sensor, according to claim 1, where the sensor is adapted for use directly connected to the face of the patient such that the sensor is somehow disposed into the exhaled airstream, such as on the upper lip and directly below the nostril.
S A respiration rate sensor apparatus, according to claim 1, whereupon the patient breathes over the sensor and causes the sensor to respond to changes in water vapour concentration.
6 A respiratory rate sensor apparatus, according to claim 5, comprising a microcontroller connected to said sensor, capable of controlling the signals to and from the sensor and determining a rate of respiration from the readings of water vapour.
7 A respiration rate sensor apparatus, according to claim 5, further comprising means of transmitting respiration data from said microcontroller to a remote location.
8 A respiration rate sensor and respiration rate sensor apparatus, according to claims 5 and 7, further comprising an alarm function whereby if signals fall below prescribed limits or fail altogether, an alarm is activated.
9 A sensor for detecting water vapour in a gas stream, the sensor comprising: * afirstelectrode; * a second electrode; * an active coating material extending over and between the first and second electrodes, the nature of the coating material being selective to water vapour, such that the presence of water vapour varies the electrical conductivity of the path between the first and second electrodes.
The sensor according to claim 9, wherein the conductivity of the path between the first and second electrodes provides an indication of the concentration of water vapour in the gas stream.
11 The sensor according to claim 9 or 10, wherein the active coating material comprises a Zeolite or a silicate.
12 The sensor according to claim 11, wherein the active coating material comprises Zeolite 4A or Zeolite 13X.
13 The sensor according to any preceding claim, wherein the coating material comprises a porous material, having a pore diameter substantially the same as a water molecule, or less.
14 The sensor according to any preceding claim, wherein the first and second electrodes comprise a metal selected from Group VIII, gold, copper and silver.
The sensor according to any preceding claim, wherein the sensor further comprises an inert support.
16 The sensor according to claim 15, wherein the active coating is disposed on a surface of the inert support and the first and second electrodes are disposed on the surface of the coating.
17 The sensor according to claim 15, wherein at least one of the first and second electrodes is disposed between the coating and the inert support.
18 A method of detecting water vapour in a gas stream, the method comprising: * contacting the gas stream with an active coating extending between first and second electrodes; * determining the variation in the electrical conductivity of the path between the first and second electrodes; and * providing an indication of the presence of the target component in the gas stream.
19 The method of claim 18, wherein the conductance of the path between the first and second electrodes is determined and provides an indication of the concentration of the target component in the gas stream.
The method of claim 18 or 19, wherein a voltage is applied to the first and second electrodes.
21 The method of claim 20, wherein the voltage is constant or varied over time.
22 A method of analyzing the exhaled breath of a person or animal, the method comprising: * causing the exhaled breath to contact an active coating extending between first and second electrodes; * determining the variation in the electrical conductivity of the path between the first and second electrodes; and * providing an indication of the water vapour content of the exhaled breath.
23 A method of determining a person's or animal's respiration comprising the steps of: * Breathing across the surface of the water vapour sensor * Generating a signal with varying amplitude and frequency proportional to respiratory air flow and volume If, * Electronically monitoring the water vapour signal, and * Interpreting said water vapour signature to reflect the rate of breathing
24 A method of monitoring a person's or animal's respiration according to claim 23, further comprising the steps of transmitting the data to a remote location for viewing by a healthcare professional.
A method of monitoring a person's or animal's respiration according to claim 23, further comprising the steps of monitoring respiratory signals from the water vapour sensor to determine respiratory condition; and automatically activating an alarm if respiratory parameters fall outside user-selectable values (thresholds) including at least one of: i) rate fluctuations in respiration, ii) incrfeaed inhalation, iii) decreased inhalation, iv) exhalation/inhalation time ratios, and v) fluctuations in respiratory water vapour signatures.
26 A method for determining a patient's or animal's respiration according to claim 23, further comprising activating an alarm if the water vapour signal drops by a predetermined value over a predetermined period of time.