Non-invasive estimation of arterial blood gases
First Claim
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1. A non-invasive arterial gas partial pressure determination system, comprising:
- expiratory gas sampling means for taking one or more samples of expiratory gases from a patient;
means for assessing said gas partial pressure with respect to expiratory volume for said sampled gas;
means for evaluating said sampled gas in terms of said assessed gas partial pressure and expiratory volume iteratively during an exhale cycle to develop a multi-variable relationship; and
gas sampling data processing means for receiving data input representative of said multi-variable relationship and selectively processing said data input to determine at least one arterial gas partial pressure value for that patient.
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Abstract
A non-invasive system and procedure for deriving the blood gas content for a patient. The system measures the carbon dioxide concentration of the expiratory breath relative to volume. This data is then processed to derive arterial blood gas levels of carbon dioxide. If data sampling is in the time domain, the processing shifts the data from the time domain to the volume domain. The processing also iteratively assesses the significance of numerous variables. The resulting relationship provides a fast and accurate measure of blood gas content for both healthy and diseased lung patients.
68 Citations
19 Claims
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1. A non-invasive arterial gas partial pressure determination system, comprising:
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expiratory gas sampling means for taking one or more samples of expiratory gases from a patient; means for assessing said gas partial pressure with respect to expiratory volume for said sampled gas; means for evaluating said sampled gas in terms of said assessed gas partial pressure and expiratory volume iteratively during an exhale cycle to develop a multi-variable relationship; and gas sampling data processing means for receiving data input representative of said multi-variable relationship and selectively processing said data input to determine at least one arterial gas partial pressure value for that patient. - View Dependent Claims (2, 3)
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4. A computer controlled data collection and processing method for monitoring arterial gas values for at least one gas, comprising:
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sampling a patient'"'"'s exhaled breath to determine a partial pressure of said at least one gas in said exhaled breath as a function of incremental breath volume during an exhale cycle; segregating data from said functional determination into three distinct phases representative of gas concentration of said at least one gas during said exhale cycle; extracting functional variables from at least two of said three distinct phases in terms of slope and intercept values; recalling from memory a matrix of weighting parameters associated with said extracted functional variables; creating a vector based on said extracted functional variables modified by said recalled weighting parameters; and determining an arterial gas value for said at least one gas based on said vector. - View Dependent Claims (5, 6, 7, 8)
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9. A system for deriving blood gas concentration for a patient for at least one gas, comprising:
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a) data acquisition means for measuring exhaled breath from said patient and determining concentration of at least one gas fraction thereof at volumetric increments of said exhaled breath; and b) data processing means for receiving data representative of said at least one determined concentration and extracting select parameters therefrom to form a relationship, and implementing said relationship to derive said blood gas concentration for said at least one gas. - View Dependent Claims (10, 11, 12, 13)
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14. A non-invasive method of determining blood gas content based on volume domain, comprising:
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a) taking time domain measurements of a plurality of a patient'"'"'s expiratory breath during at least one respiratory cycle using a pneumotachometer, and a gas sensor for sensing the concentration of said blood gas in said breath, said measurements being at a frequency approximately between 10 and 1000 Hz; b) converting said time domain measurements to the volume domain; c) mapping said volume domain data to form a curve; d) determining a threshold point having a value for said concentration of said blood gas in said breath, whereat said curve transcends from a value below said threshold point value to a value above said threshold point value; e) calculating a first phase slope for said curve wherein said threshold point is an initial phase point, plotting subsequent points until said points deviate from a linear path, said deviation indicating the termination of said first phase; f) calculating a second phase slope for said curve by taking a last data point of expiration during said at least one respiratory cycle and regressing toward the termination point of said first phase; g) extracting first phase and second phase slope values to create an expiratory relationship; h) combining said expiratory relationship with stored arguments into at least one vector; i) using said at least one vector to produce an estimate of the concentration of said blood gas in said blood; and j) visually displaying said gas content in said blood. - View Dependent Claims (15, 16, 17)
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18. A non-invasive method of determining a dissolved gas content of an arterial portion of a patient'"'"'s pulmonary vasculature expressed as a partial pressure comprising:
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a) taking time domain measurements of a plurality of said patient'"'"'s expiratory breaths using a pneumotachometer and gas sensor, at a frequency of about 100 Hz; b) converting said time domain measurements to a volume domain; c) mapping a curvature relationship of gas partial pressure versus gas volume; d) determining a threshold point, said threshold point being the point where said curvature relationship transcends from a value below 0.5% of said gas partial pressure to a value above 0.5%; e) calculating a first phase slope wherein said threshold point is an initial point and including plotting subsequent points until said points deviate from a linear path, said deviation indicating termination of said first phase; f) calculating a second phase slope by taking a last data point of expiration and regressing toward the termination point of said first phase; g) using the first and second phase slopes to quantify an expiratory gas relationship; h) combining said relationship with stored arguments into at least one vector; i) using said at least one vector to estimate partial pressure of said dissolved gas; and j) visually displaying said partial pressure of said dissolved gas. - View Dependent Claims (19)
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Specification