Patent Application
20140371619
Exhaled human breath typically consists of approximately 78% nitrogen, 15-18% oxygen, 4-6% carbon dioxide, and 5% water. The remaining small fraction of exhaled breath generally consists of trace levels of more than 1000 volatile organic compounds (VOCs) with concentrations ranging from parts per trillion (pptv) to parts per million (ppmv).
Acetone is a VOC in exhaled human breath that can indicate various health conditions such as diabetes, heart disease, epilepsy, and others. For example, a person with diabetes who is in a state of ketosis will have an increased breath concentration of acetone resulting from the body's production of ketone bodies. Acetone is also produced by ketosis resulting from a restricted calorie weight loss and/or exercise program. This acetone production is the result of metabolism of fat. Hence, a breath acetone content measurement can be used as an indication of a medical condition or of fat burning during a diet and/or program to show the effectiveness of the program. These examples should be considered non-limiting in that the present disclosure can be directed to any situation in which breath acetone levels are to be detected and/or monitored.
The present disclosure is directed to an acetone sensor useful for detecting various health conditions and/or for monitoring the efficacy of diet and exercise programs. The acetone level for diet and exercise is lower than that caused by diabetes. Accordingly, a more sensitive sensor is required to monitor increased acetone levels caused by diet and exercise. Thus, there is a need for an acetone sensor capable of detecting acetone levels corresponding to diet and exercise induced ketosis.
A first embodiment of a disclosed breath analyzer detects a particular breath component in a breath sample. The analyzer includes a housing defining an interior cavity and having an inlet aperture for receiving the breath sample and an outlet aperture. A sensor is disposed within the cavity for sensing the component of the breath sample. An anemometer circuit is associated with the sensor and measures a rate of flow of the breath sample within the housing. The analyzer further includes a controller operatively connected to the sensor to receive breath component information sensed by the sensor.
A second disclosed embodiment of a breath analyzer detects a breath component in a breath sample. The breath analyzer includes a housing that defines an interior cavity and includes an inlet aperture for receiving the breath sample and an outlet aperture. A metal oxide sensor is disposed within the cavity for sensing the component of the breath sample. The analyzer further includes a temperature control system integrally formed with the sensor. The temperature control system has a metal resistor with a positive temperature coefficient. The metal resistor is configured to heat the sensor to a predetermined temperature and to sense the temperature of the sensor. The metal resistor is integrally formed with a closed-loop control that selectively controls the metal resistor. The closed-loop control circuit is configured to measure a rate of flow of the breath sample within the housing. A controller operatively connected to the sensor to receive breath component information sensed by the sensor.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
This present disclosure relates to a device for detecting the concentration of a particular breath component, such as acetone, using a metal oxide sensor in combination with a temperature control system. The temperature control system uses a closed loop control both to sense the sensor operating temperature and to heat the sensor as necessary to achieve the desired sensor operating temperature. Metal oxide based gas sensors typically require operation at relatively high temperatures (e.g. 300 C). The sensitivity of the sensor to a given gas is often highly dependent on the sensor temperature. Therefore the ability to directly monitor and control sensor temperature is advantageous. Accurate thermal control becomes especially critical when attempting to detect gases that are present at very low concentrations such as with the acetone vapor found in breath as a result of diet and exercise. The present disclosure relates to the temperature control system used to achieve the desired sensor operating temperature, and the advantageous use of the heating element itself as the temperature measurement device.
While the present disclosure and exemplary embodiments are generally described with respect to devices used to detect acetone content in a breath sample, such embodiments are exemplary only and should not be considered limiting. In this regard, the described sensors can be sensors for detecting levels of gaseous breath components other than acetone, including VOCs and other gaseous compounds. Further, it will be appreciated that the sensors are not limited to sensors used for detecting components from breath samples, but can include sensors used to detect components of any other suitable gas sample.
A cavity 112 is formed in a central portion of the collector 102 in fluid communication with the inlet aperture 106 and the outlet aperture 108. A sensor assembly housing 114 is positioned between the first and second ends of the elongate body and defines a sensor assembly cavity 116 in fluid communication with the cavity 112 of the elongate body 104. A sensor assembly 200 is disposed within the sensor assembly housing 114.
The sensor assembly 200 is operatively connected to a processor 118. As described in further detail below, the processor 118 receives data from the sensor assembly 200 related to sensed breath components, breath flow, sensor temperature, and other operating characteristics. In one contemplated embodiment, the processor 118 processes the data and selectively displays the information received from the sensor assembly 200 on a display (not shown) for the user. In yet another contemplated embodiment, the processor 118 stores the data locally, or makes the data available for transfer to a remote storage location or processor, such as a home computer, tablet, smart phone, etc. These and other processor functions suitable for receiving and processing diagnostic data are contemplated and should be considered within the scope of the present disclosure.
The disclosed configuration is suitable for collecting a breath sample from a user and exposing the breath sample to the sensor assembly 200 for analysis. For acetone detection, it is preferable that the analyzed breath sample be alveolar air, i.e. air from deep within the lungs. While some alveolar air is generally exhaled during the entire exhalation, in a preferred embodiment, the sample is taken from the last third of the exhalation to maximize the amount of deep-lung air in the sample. The illustrated device 100 collects and isolates alveolar air for analysis. To utilize the device 100, a user places his mouth to the mouthpiece and blows a long, continuous breath sample into the inlet aperture 106. The breath sample flows through the cavity 112 in the direction indicated by the arrow and then exits through the outlet aperture 108. The outlet aperture 108 has a reduced geometry that limits the flow of breath out of the cavity 112. In this manner, the breath sample is contained within the device 100 until after the sensor assembly 200 has analyzed the breath sample.
In the illustrated embodiment, the substrate 202 is an alumina substrate with tungsten oxide (WO3) coating 212 deposited thereon. It will be appreciated that metal oxide gas sensors are known in the art and the described WO3 coating 212 disposed on an alumina substrate 202 is exemplary only. In this regard, other metal oxides or combination of metal oxides suitable for sensing acetone and alternate substrate materials are possible and should be considered within the scope of the present disclosure. Further, the disclosed sensor 210 is not limited to the use of metal oxide gas sensors made using any particular manufacturing method. It will also be appreciated that the substrate 202 is not limited to an aluminum oxide material, but can alternatively be formed of glass, other suitable high-temperature substrates, or a combination thereof. Exemplary metal oxide gas sensors and/or methods of forming the same are disclosed in U.S. Patent Publication Nos. 2011/0071446 and 2003/0217586, the disclosures of which are expressly incorporated herein by reference.
In the illustrated embodiment, the surface area of the sensor 210 is approximately 1 mm2; however, other embodiments are contemplated wherein the surface area of the sensor is larger or smaller than that of the illustrated embodiment. Because the surface area of the sensor is relatively small, the sensor heats-up and cools-down quickly. Metal oxide gas based sensors, such as the disclosed acetone sensor 210, typically require relatively high operational temperatures, e.g., about 300° C. The sensitivity of the sensor to a given gas is often highly dependent on the sensor temperature. Accordingly, the ability to directly monitor and control sensor temperature is advantageous.
Accurate thermal control becomes especially critical when attempting to detect gases that are present at very low concentrations such as with the acetone vapor found in breath. The presently disclosed the acetone sensing device 100 incorporates a heating element to achieve the desired sensor operating temperature, and uses of the heating element itself as the temperature measurement device. Utilizing the temperature control system 220 enables the operating temperature of the acetone sensing device 100 to be maintained within a range of approximately 300° C. to 450° C. It will be appreciated that this range is exemplary only and that the actual range of the sensor operating temperature can be modified to be suitable for a particular type of sensor. Further, the operating temperature of the sensor can be maintained within a narrower range to provide increase accuracy.
Still referring to the embodiment of
In order to minimize self-heating, typical RTD resistance sensing is conducted in a manner that minimizes the power applied to the RTD. Moreover, platinum is generally not used as a base material for resistive heaters due to its high cost. However, the disclosed temperature control system 220 requires a relatively small heater so that it is feasible to use the RTD itself as the resistive heating element. Integrating a resistive heating element with a temperature sensor in a single temperature control system 220 allows for significant advantages, including reduced cost, reduced sensor complexity, fewer interconnecting leads, and intimate thermal contact between heater and temperature sensor.
The operational amplifier 402 controls the voltage so that the temperature of the RTD is such that the resistance of the RTD balances the circuit. With the R1, R2, and RVAR having known values, the circuit is balanced when the resistance or the RTD, is at a specific value, as defined in equation (2) below.
The value of RRTD corresponds closely to a specific RTD temperature, so that the equation is balanced when the RTD is at a predetermined temperature. In this manner, the operational amplifier 402 controls the voltage to maintain a predetermined RTD temperature.
The circuit works by the operational amplifier 402 continuously balancing its inputs, VIN+ and VIN−, as shown below in Equation 3.
When the RTD is below the temperature setpoint, its resistance is lower. Accordingly, the operational amplifier 402 input VIN− is lower than VIN+, which causes VOUT to increase. When VOUT increases, more power is delivered to the RTD, raising its temperature. Conversely, when the RTD is above the temperature setpoint, its resistance is higher. In this case, the operational amplifier 402 input VIN− is higher than VIN+, which causes VOUT to decrease, delivering less power to the RTD and cooling it. Accordingly, the known value of R1 can be used along with the measured values of VIN− and VOUT to calculate the resistance and, therefore, the temperature, of the RTD.
In addition to providing the ability to maintain a particular RTD temperature and also to sense the temperature of the RTD, the disclosed circuit 400 is also suitable for use as an anemometer. When used with the acetone sensing device 100, the heater/temperature sensor circuit 400 is subjected to a breath sample being blown past the sensor. As the breath flows past the sensor circuit 400, the effects of forced convective heat transfer requires more power to the RTD to maintain a constant temperature. Because the characteristics of the exhaled breath are known, e.g., 37° C. (body temperature for a human) with a relative humidity of ˜100%, the added power used to maintain a constant RTD temperature, which is related to cooling rate due to forced convective heat transfer, can be used to calculate the rate of flow of the breath sample as the user breathes into the acetone sensing device. Other embodiments of constant temperature anemometers are disclosed in U.S. Pat. No. 5,069,066, the disclosure of which is expressly incorporated herein.
Using the anemometer features of the disclosed temperature control system 220, it is possible to provide an acetone sensing device 100 that senses whether or not a breath sample is suitable for analysis. As previously discussed, it is preferable that the breath sample to be analyzed is from approximately the last third of a full, breath expiration. In one contemplated embodiment, the acetone sensing device 100 senses the flow rate of breath through the device and requires that the user maintain a minimum breath flow rate for a threshold amount of time before beginning acetone detection.
The circuit 500 includes an RTD connected in series with a shunt resistor, Rshunt. A microprocessor 502 provides an excitation voltage (Vexcitation) to the RTD. The junction between the microprocessor 502 and the RTD is connected to an analog input of the microprocessor 502 feeding Vexcitation back to the microprocessor. In addition, the junction between the RTD and Rshunt is connected to a second analog input of the microprocessor 502 feeding Vshunt to the microprocessor. The circuit acts as a resistive divider, wherein the relationship of Vshunt to Vexcitation is shown in equation (4).
As previously noted, for a given RTD, a particular value RRTD corresponds closely to a particular temperature of the RTD. To achieve a known RRTD-SETPOINT and the corresponding target RTD temperature, the microprocessor 502 controls Vexcitation according to equation (5).
The closed-loop feedback provided through the microprocessor 502 combined with the close correlation between the resistance and the temperature of the RTD allows for the circuit 500 to also be used as a temperature sensor and as an anemometer in the manner previously described with respect to the circuit 400 of
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/834,647, filed Jun. 13, 2013, the entire disclosure of which is hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61834647 | Jun 2013 | US |
