Method and Apparatus for Effective Detection of Respiratory Blockage Using CO2 Monitor

Abstract

A system and method are provided to detect a possible respiratory blockage by using personalized carbon dioxide (CO.sub.2) concentration change patterns without concerning its absolute values. The personalized change patterns can intelligently learn new change pattern to increase its accuracy. Advanced pattern recognition is used to detect abnormal CO.sub.2 concentration change pattern by comparing to personalized patterns, and allowing the system to trigger alarm to alert a caregiver or a guardian.

Claims

1. A method for detecting respiratory blockage, comprising: attaching a housing with a carbon dioxide (CO.sub.2) sensor to a region of a person's skin; warming said region of said person's skin to a preset temperature; collecting non-dissolved CO.sub.2 gas emitted from said region of said person's skin; determining, by a processing circuit, the change pattern of said collected non-dissolved CO.sub.2 gas by analyzing its concentration waveforms and slopes without relying on its absolute CO.sub.2 concentration values; comparing the determined change pattern of said collected non-dissolved CO.sub.2 gas to a set of stored personalized CO.sub.2 change patterns; and signaling an alarm when the difference from said compared result is beyond a preset threshold.

2. The method of claim 1, wherein said analyzing waveforms and slopes of said collected non-dissolved CO.sub.2 includes tracking the occurrence of a beginning slope and an ending slope of a CO.sub.2 concentration curve and the time between said beginning slope and said ending slope.

3. The method of claim 1, wherein said set of personalized CO.sub.2 change patterns include a plurality of CO.sub.2 change patterns created under different types of personal activities.

4. The method of claim 3, wherein said different types of personal activities include quiet activities, mild physical activities and vigorous physical activities.

5. The method of claim 3, further comprising using heart rate change information to identify activity and select appropriate activity type of personalized CO.sub.2 change patterns for comparison.

6. The method of claim 1, further comprising adding said change pattern of said collected non-dissolved CO.sub.2 gas to said set of stored personalized CO.sub.2 change patterns when said alarm is determined to be false.

7. A system for detecting respiratory blockage, comprising a housing with a carbon dioxide (CO.sub.2) sensor for attaching to a region of a person's skin; a device in said housing warming said region to a temperature to a preset temperature; an vacuum pump collecting said non-dissolved CO2 gas emitted from said region of said person's skin for CO2 sensor's detection; a processing circuit connected to said CO2 sensor and operates to: determine the change pattern of said collected non-dissolved CO2 gas by analyzing the waveforms and slopes of said collected non-dissolved CO2 concentration without relying on its absolute CO2 concentration values; compare the determined changed pattern of said collected non-dissolved CO2 gas to a set of stored personalized CO2 change patterns; and trigger an alarm when the difference from said compared result is beyond a preset threshold.

8. The system of claim 7, wherein said analysis of waveforms and slopes of said collected non-dissolved CO.sub.2 includes tracking the occurrence of a beginning slope and an ending slope of a CO.sub.2 concentration curve and the time between said beginning slope and said ending slope.

9. The system of claim 7, wherein said set of personalized CO.sub.2 change patterns include a plurality of CO.sub.2 change patterns created under different types of personal activities.

10. The system of claim 9, wherein said different types of personal activities include quiet activities, mild physical activities and vigorous physical activities.

11. The system of claim 7, further comprising a heart rate sensor configured to detect heart rate change to identify activity and select appropriate activity type of personalized CO.sub.2 change patterns for comparison.

12. The system of claim 7, wherein said system adds said change pattern of said collected non-dissolved CO.sub.2 gas to said set of stored personalized CO.sub.2 change patterns when said alarm is determined to be false.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0006] The present disclosure is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0007] FIG. 1 is a generalized block diagram illustrating a CO.sub.2 monitor system applied to human skin, according to an embodiment;

[0008] FIG. 2A illustrates a graph of CO.sub.2 concentration level measured under different activities, according to an embodiment;

[0009] FIG. 2B illustrates another graph of CO.sub.2 concentration level measured under different activities, according to an embodiment;

[0010] FIG. 3 is a flow chart illustrating steps for the operation of a monitor system, according to an embodiment;

[0011] FIG. 4 is a flow chart illustrating steps for the operation of a monitor system, according to an embodiment;

[0012] FIG. 5 is a flow chart illustrating steps for the operation of a monitor system, according to an embodiment.

[0013] FIG. 6 is a block diagram illustrating a signal processing circuit, according to an embodiment.

DETAILED DESCRIPTION

[0014] It is desirable to have a wearable, portable monitor that can monitor internal blood CO.sub.2 levels of humans in order to prevent deaths caused by respiratory blockage, such as by choking or by asthma. Currently, there are no known device designs that allow continuous monitoring of the blood CO.sub.2 levels of a patient or individual outside of an intensive care unit or by allowing individuals to partake in everyday activities, and this disclosure is aimed at solving this problem. In addition, the present disclosure tries to overcome the problem of residual CO.sub.2 from environment when using CO.sub.2 sensors to detect diffused CO.sub.2 emitted from a person's skin by not relying on its absolute concentration values.

[0015] In the following description, numerous specific details are set forth to provide a thorough understanding of the methods and mechanisms presented herein. However, one having ordinary skill in the art should recognize that the various embodiments may be practiced without these specific details. In some instances, well-known structures, components, signals, computer program instructions, and techniques have not been shown in detail to avoid obscuring the approaches described herein. It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements.

Advantages of Measuring Arterial pCO.sub.2

[0016] The analysis of the partial pressure of carbon dioxide in arterial blood, pCO.sub.2, is of great significance in medical diagnosis because pCO.sub.2 is an indicator of alveolus ventilation and the acid-base balance of the human body. In particular, the continuous monitoring of arterial pCO.sub.2 is essential for surgical and serious patients who depend on an artificial ventilator. However, the blood-sampling method has restrictions, which makes it very invasive to patients, and needs much time for analysis because blood is directly obtained from the human body. In other cases of emergency in which patients require noninvasive analysis, arterial p CO.sub.2, is inferred from end-tidal carbon dioxide, EtC02, analysis, which does not accurately determine the arterial pC02 and is very inconvenient because patients should breathe through a catheter. On the other hand, it is known that transcutaneous pC02 measurement results agree with those of arterial blood pC02 measurement, which is determined by blood-sampling method. Moreover, it has merits such as the arterial pC02 in a capillary vessel can be measured in real time.

Basic Components of a CO.SUB.2 .Monitor System

[0017] FIG. 1 illustrates a general block diagram of the basic components used for collecting and measuring diffused CO.sub.2 from skin. In an embodiment, a CO.sub.2 monitor system 100 comprises a skin-mount pad 101 warming the skin and capable of adjusting temperature between 37 C. and 42 C. to obtain diffused CO.sub.2 gas. The warming pad 101, such as thin metal strip or coiled wire sandwiched between non-conductive material that allows heat to pass through, is inside a cover 106 and not directly in contact with skin, but could warm the skin to allow CO.sub.2 diffusion. The CO.sub.2 monitor system 100 also includes a Non-Dispersive Infrared (NDIR) CO.sub.2 sensor 102 for measuring the pCO.sub.2 level. NDIR CO.sub.2 sensor 102 is used here for its sensitivity, accuracy and miniature size but other types of CO.sub.2 sensor may be used as long as they can serve the same purpose. A vacuum pump 103 with adjustable flow rate is connected to a NDIR CO.sub.2 sensor to move the collected diffused CO.sub.2 gas to the CO.sub.2 sensor for measurement. The circulation rate of vacuum pump should be close to the pCO.sub.2 diffusion rate of skin. If the CO.sub.2 sensor is sufficiently close to the skin and can sense CO.sub.2 gas emitted from the skin quickly, the vacuum pump 103 may not be needed. In other words, the CO.sub.2 gas to be measured is collected outside a person skin, not dissolved below a person's skin or in human tissue. Depending on the types of CO.sub.2 sensor, a vacuum pump may or may not be used. A signal processing circuit 104 connected to NDIR CO.sub.2 102 sensor is used to continuously record and calculate the changing pattern of pCO.sub.2 level and trigger an alarm when an unusual pattern occurs, a pattern that indicates a likelihood of respiratory blockage, such as choking or asthma attack. The alarm signal is transmitted to the guardian of an infant or a child or to a caregiver. The alarm may be an audio signal to alert nearby help or a wireless signal transmitted to guardian's or caregiver's mobile devices or emergency centers such as 911 or hospital. In another embodiment, skin-mount pad 101 with temperature control 105, vacuum pump 103, CO.sub.2 sensor 102, signal processing circuit 104 and alarm (not shown) may be integrated together as one portable unit, such as a small electronic patch on skin, and be made waterproof. Additionally, a heart rate sensor 108 may be optionally used to detect the heart rate change, which will be described in more detail later.

Mechanism of Respiratory Blockage Detection

[0018] In order to trigger alarm for abnormal CO.sub.2 changes, the detected CO.sub.2 level does not have to be accurate in its absolute value but needs to be consistent. Therefore, a high temperature may not be necessary to obtain a large amount of diffused CO.sub.2 gas, and thus a lower temperature of 40 C. or below may be sufficient. Consequently, the CO.sub.2 monitor system can be worn by an individual for a considerable time or even 24 hours without causing any discomfort.

[0019] When a person is in healthy condition and behaving normally, the detected pCO.sub.2 level should stay roughly the same. It may also move to a different level and then stabilize when the person engages in a different activity, such as dancing, walking or exercise. However, when a respiratory blockage occurs, the detected pCO.sub.2 level would show a continuously changing pattern as the arterial CO.sub.2 continues to build up, such as an upward trend. It is this changing pattern that helps to identify the early sign of respiration problem. Since the CO.sub.2 change is more pronounced than the O.sub.2 change when a person experiences a respiration problem, CO.sub.2 detection would be more effective in achieving an early detection of the problem.

CO.SUB.2 .Measurement and Data

[0020] FIGS. 2A and 2B illustrate the change of CO.sub.2 level in various conditionsnormal and blockage of air passage. Normal condition may include quiet activity, mild activity and rigorous activity. In FIG. 2A, the CO.sub.2 monitor system 100 is calibrated to open air as illustrated in section 202 of the graph. Once the CO.sub.2 monitor system 100 is applied to a test subject (e.g. a person) in a way that does not obstruct the person's daily activity, such as wrist, arm or shoulder, the CO.sub.2 level increases gradually and eventually stabilizes as shown in section 204. When the person engages in a mild activity that increase the heart rate such as walking, the CO.sub.2 level changes again and then stabilizes as shown in section 206. Occasionally, when a person engages in an vigorous activity such as running or biking, the CO.sub.2 level may jump in a short period of time and fall back to normal level when the heart rate decreases as shown in dash line of section 208.

[0021] In FIG. 2B, section 202 illustrates the calibration period to open air. When a person, the test subject, is in a quiet activity such as sitting and reading a book, the CO.sub.2 level is stabilized as in section 204. When respiratory blockage occurs, (or the test subject holds his/her breath), the CO.sub.2 level starts to change and continues to increase for a prolonged period of time, as in section 210, as long as the blockage condition is not cleared. When this changing pattern continues for a certain amount of time, an alarm may be triggered to notify guardians or caregivers.

[0022] Typically, the CO.sub.2 concentration of calibrated value to open air is around 400 parts per million (ppm) at sea level as shown in section 202 of FIGS. 2A & 2B. When the CO.sub.2 monitor system is applied to a human skin, the CO.sub.2 concentration could rise up to a few thousand ppm (e.g. 1,0005,000 ppm) and stabilize as shown in section 204 of FIGS. 2A & 2B. However, when a person engages in a vigorous activity, the CO.sub.2 concentration could increase a few thousand ppm in just tens of seconds and then stabilize as shown in section 208 of FIG. 2A. When a respiratory blockage occurs, CO.sub.2 concentration may increase between tens to hundreds of ppm continuously for a long period of time depending on severity of the blockage condition as shown in section 210 of FIG. 2B.

[0023] The CO.sub.2 concentration values in FIGS. 2A and 2B are for illustration only, not absolute values since these values may vary depending on person's health condition, measuring devices and environmental conditions. However, the general trends (or patterns) illustrated in FIGS. 2A and 2B are substantially the same and consistent for different persons.

[0024] In order to detect the changing pattern or trend of CO.sub.2 level, a moving average may be used for this purpose. The moving average calculates an average value of a subset of data within a certain period of time or window, for example, the data collected within the past 2 seconds or 5 seconds. The calculation repeats on different subsets of data as the window moves (i.e. center of the subset changes). To make the CO.sub.2 monitor system more sensitive to the change or shorter trend, the system can be configured to use a smaller window. Likewise, the CO.sub.2 monitor system can be configured to use a larger window to detect longer trend.

[0025] Alternatively, the slopes of a changing curve of CO.sub.2 level may be used. For example, the beginning slope and the ending slope of a curve together with the time between these two slopes may be used to recognize the trend of CO.sub.2 level change. Typically, the CO.sub.2 curve of a vigorous activity is steep and stabilizes within a short period of time. In addition to the previously discussed methods, other methods for detecting CO.sub.2 level change may be contemplated.

[0026] Since each person may have unique CO.sub.2 level patterns, the CO.sub.2 monitor system may create a personalized database for each user and use advanced pattern recognition techniques to quickly detect an abnormal CO.sub.2 level change. In one embodiment, the CO.sub.2 monitor system may request a user to perform a few basic daily activities such as quite activity (e.g. lying still), mild activity (e.g. walking), and vigorous activity (e.g. running) for one to two minutes each. Then the system can record CO.sub.2 level patterns associated with these activities for the particular user and store as a personalized database for future comparison. In another embodiment, the CO.sub.2 monitor system may intelligently learn the user's daily activities through the user's interaction (e.g. when user indicates a false alarm) and categorize the corresponding CO.sub.2 level patterns for future use, to be illustrated later.

Configuration Modes of CO.SUB.2 .Monitor System

[0027] The CO.sub.2 monitor system 100 may be configured to provide different levels of alerts when detecting a likely respiratory problem. In one embodiment, as shown in FIG. 3, the monitor may be configured to trigger an alarm for any abnormal change in CO.sub.2 level for early warning and the warning level can be set to yellow color to indicate a possible concern. For example, when a CO.sub.2 level pattern deviates from recorded basic personalized patterns in the database at any time, the system may trigger a warning. Once the guardian or caregiver confirms it is a false alarm, the system can learn from this pattern and add it to the personalized database. For example, when the alarm is triggered and the guardian determines that no health problem occurs or the user's activity creates an unusual CO.sub.2 pattern, it would be deemed a false alarm and the new CO.sub.2 pattern is added to the personalized database.

[0028] In FIG. 3, at step 302, they system pre-records personalized CO.sub.2 patterns under different conditions and activities (e.g. quiet activity, mild activity and vigorous activity), as described earlier referring to FIG. 2A. At step 304, the system detects a CO.sub.2 pattern change, then it compares the change to the pre-recorded personalized patterns stored in database as in step 306. At step 308, if the change pattern matches the personalized data, the system continues to monitor and detect any future pattern change. If the change pattern does not match the personalized data, the system triggers an alarm at step 310. At step 312, a caregiver or a guardian or the user can check whether it is a false alarm. If it is a false alarm, the user can simply acknowledge and allow the system to add the pattern to the personalized database. If it is not a false alarm, the emergency alarm has achieved its purpose at step 314. Since the recorded CO.sub.2 pattern is a personalized data, the system should not trigger too many false alarm, and the accuracy increases dramatically after learning a few unusual patterns.

[0029] In another embodiment, as shown in FIG. 4, the monitor can be configured to trigger an alarm when it detects a trend of abnormal changes, for example a steady increase in moving average of CO.sub.2 level beyond a certain period of time. Yet in another embodiment, the trend of change can be set to duration of 10 seconds, 20 seconds or 30 seconds, etc. Usually, such prolonged trend of CO.sub.2 level change is a likely indicator of respiratory blockage and the alarm level can be set to red to indicate a severe condition for immediate attention. Yet in another embodiment, the CO.sub.2 monitor system may record visual information of the CO.sub.2 changing pattern for a certain period of time, so the guardian or caregiver can review the history that contributes to the trigger of an alarm.

[0030] In FIG. 4, at step 402, the CO.sub.2 monitor system detects a pattern change. At step 404, the system can utilize one of the methods mentioned earlier to determine the CO.sub.2 change trend within a certain period of time. At step 406, if the system detects the relation between the change trend and time duration is beyond a preset threshold, the system triggers an alarm at step 408. Otherwise, the system continue to monitor any CO.sub.2 pattern change or deviation.

Consideration of Human Factors

[0031] As discussed earlier, different human activities may create different CO.sub.2 level and one factor that associates with these activities is the heart rate. Therefore, in one embodiment, the CO.sub.2 monitor system may incorporate a heart rate sensor to help interpret CO.sub.2 level changes besides checking personalized CO.sub.2 pattern database. For example, when heart rate increases, decreases or stay constant, there will be corresponding changes in patterns of CO.sub.2 level, which may be stored as standard patterns. If a detected CO.sub.2 level pattern is different from expected patterns (either standard patterns or personalized patterns or both), it is likely that respiratory problem has occurred and an alarm may be triggered. FIG. 5 illustrates the use of both standard heart rate CO.sub.2 patterns and personalized CO.sub.2 patterns in CO.sub.2 monitor system.

[0032] At step 502, the CO.sub.2 monitor system incorporates some standard heart rate CO.sub.2 patterns that normally occur in human body. At step 504, the system pre-records some personalized CO.sub.2 patterns. By taking into account the heart rate change of the user to further supplement the personalized patterns, the system has further knowledge about the activities of the user and can select the appropriate pattern category, such as quiet, mild or vigorous category, for comparison. Alternatively, the system can separate these standard heart rate patterns and personalized patterns, and allows to select either one for use. At step 506, the system monitors and detects any CO.sub.2 pattern changes in the user's body. At step 508, the system compares the monitored pattern to the hybrid patterns to detect any deviation. At step 510, if there is a match, the system continues to monitor body CO.sub.2 pattern change. If there is a mismatch or substantial difference, the system triggers an alarm at 512. At step 514, a caregiver or a guardian or the user can check whether it is a false alarm. If it is a false alarm, the user can simply acknowledge and allow the system to add the pattern to the personalized database, as in step 504. If it is not a false alarm, the emergency alarm has achieved its purpose at step 516.

[0033] In addition to human activities, the easy use and comfort of a CO.sub.2 monitor system are important to a wearer of such device. Besides miniaturizing the monitor system (or device) to allow a person to wear on any part of its body without noticing it, the comfort of using the device may affect a person's willingness. In one embodiment, the skin-mount pad may include several small heating apparatuses that can turn on and off alternatively to achieve constant temperature around the skin while reducing a prolonged heating of a particular spot on skin. For example, four small heating apparatuses may be used and each one may be turned on for an hour and rotate around these apparatus to avoid heating the same spot on wearer's skin.

Consideration of Environmental Factors

[0034] Since temperature and air pressure may affect CO.sub.2 concentration level, some compensation mechanisms may be used. For example, the CO.sub.2 monitor system may incorporate a temperature/pressure sensor which helps take environmental factors into account. The environmental factors may include ambient temperature change (e.g. room temperature), air pressure change (e.g. due to altitude), etc. For the purpose of consistency, in one embodiment, the CO.sub.2 monitor system may have an adjustable heating apparatus that can sense the ambient temperature and adjust its heating temperature accordingly. For example, when ambient temperature is lower than 40 C., the heating apparatus can increase heating temperature to keep the temperature inside skin-mount pad close to 40 C. for sufficient CO.sub.2 gas diffusion. However, when the ambient temperature is above 40 C., the heating apparatus may turn off and/or take into account the CO.sub.2 level change due to higher ambient temperature when determining the CO.sub.2 level pattern. Similarly, higher or lower air pressure may also change the CO.sub.2 concentration level. However, the change is minor and the long term CO.sub.2 level will stabilize and should not affect the detection of respiratory blockage.

[0035] FIG. 6 illustrates an exemplary signal processing circuit 600. The processing circuit 600 includes a processing unit 602 that has access to a storage subsystem 604 containing memory for storing information, and connects to I/O subsystem 606 and communications subsystem 608. The processing unit may execute a variety of programs in response to program codes residing in storage subsystem 604 to analyze CO.sub.2 patterns and adjust heating temperature. The I/O subsystem 606 may include user interface devices and user interface output devices. The communications subsystem 608 provides an interface for receiving data from and transmitting data to sensors (e.g. CO.sub.2 sensors and heart rate sensors) or wireless network.

[0036] In the foregoing description, embodiments of the present disclosure have been described with reference to numerous specific details that may vary from implementation to implementation. The descriptions and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the present disclosure, and what is intended by the applicants to be the scope of the present disclosure, is the literal and equivalent scope of the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction.