Non-invasive determination of conditions in the circulatory system of a subject
First Claim
1. A method for non-invasively determining a condition of the circulatory system of a subject, the subject inhaling and exhaling breathing gases during breathing, said method comprising the steps of:
- (a) measuring the amount of CO2 in the breathing gases exhaled by the subject and the CO2 concentration of the breathing gases exhaled by the subject for a first (1) breathing condition of the subject;
(b) determining at least one value of the amount of CO2 released from the circulatory system of the subject (VCO21) using the amount of CO2 in the breathing gases exhaled when the subject is in the first condition;
(c) determining at least one value for a quantity indicative of the end capillary blood CO2 content of the subject using the CO2 concentration of the breathing gases exhaled when the subject in the first condition;
(d) altering the CO2 concentration in the lungs of the subject;
(e) measuring the amount of CO2 in the breathing gases exhaled by the subject and the CO2 concentration of the breathing gases exhaled by the subject for at least one breath of the subject under a second (2) breathing condition of altered CO2 in the lungs of the subject;
(f) determining at least one value for the amount of CO2 released from the circulatory system of the subject (VCO22), the determination of the value being carried out in a time period less than that required for blood leaving the lungs of the subject to pass through the circulatory system of the subject and return to the lungs, the determination of the value using the amount of CO2 in the exhaled breathing gases for the second breathing condition;
(g) determining at least one value for a quantity indicative of the end capillary blood CO2 content of the subject, the determination of the value being carried out in a time period less than that required for blood leaving the lungs of the subject to pass through the circulatory system of the subject and return to the lungs, the determination of the value using the CO2 concentration of the breathing gases exhaled for the second breathing condition;
(h) performing a regression analysis using the determined VCO21, VCO22, and end capillary blood CO2 quantity values to establish a regression line;
(i) extrapolating the regression line to obtain a value for the end capillary blood CO2 quantity when the amount of CO2 released from the circulatory system of the subject (VCO2) is zero;
determining a further value for the quantity indicative of the end capillary blood CO2 content for breathing of the subject in the first breathing condition;
forming a relationship between the value for the quantity indicative of the end capillary blood CO2 content for breathing in the first breathing condition used in the regression analysis and the value obtained by extrapolating the regression line in step (i); and
applying the relationship to the further determined value for a quantity indicative of the end capillary blood CO2 content to provide a new value for the value which was obtained by the extrapolation of the regression line in step (i).
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Accused Products
Abstract
A method for non-invasively determining functional cardiac output (FCO) and/or venous blood CO2 partial pressure (PvCO2). The amount of CO2 (VCO2N) released from the blood and end capillary blood CO2 content (CcCO2N) are determined from measurements from exhaled breathing gases. The CO2 content of the breathing gases inhaled by the subject is increased and values for VCO2R and CcCO2R are obtained. A regression analysis is performed using the obtained VCO2N, VO2R, CcCO2N, and CcCO2R values. The regression line is extrapolated to obtain a value for CcCO2 when (VCO2) is zero so that CvCO2 becomes known. The CvCO2 thus determined can be inserted in a non-differential form in the Fick equation, along with VCO2 and CcCO2 values from normal breathing, to determine FCO. To determine PvCO2, CvCO2 is altered in accordance with the amount of oxygen in the venous blood, to correctly indicate PvCO2. The continuing validity of the FCO measurement can be examined on a breath-by-breath basis by noting changes in an indicator variable, such as VCO2 or end tidal CO2 amounts.
39 Citations
63 Claims
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1. A method for non-invasively determining a condition of the circulatory system of a subject, the subject inhaling and exhaling breathing gases during breathing, said method comprising the steps of:
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(a) measuring the amount of CO2 in the breathing gases exhaled by the subject and the CO2 concentration of the breathing gases exhaled by the subject for a first (1) breathing condition of the subject; (b) determining at least one value of the amount of CO2 released from the circulatory system of the subject (VCO21) using the amount of CO2 in the breathing gases exhaled when the subject is in the first condition; (c) determining at least one value for a quantity indicative of the end capillary blood CO2 content of the subject using the CO2 concentration of the breathing gases exhaled when the subject in the first condition; (d) altering the CO2 concentration in the lungs of the subject; (e) measuring the amount of CO2 in the breathing gases exhaled by the subject and the CO2 concentration of the breathing gases exhaled by the subject for at least one breath of the subject under a second (2) breathing condition of altered CO2 in the lungs of the subject; (f) determining at least one value for the amount of CO2 released from the circulatory system of the subject (VCO22), the determination of the value being carried out in a time period less than that required for blood leaving the lungs of the subject to pass through the circulatory system of the subject and return to the lungs, the determination of the value using the amount of CO2 in the exhaled breathing gases for the second breathing condition; (g) determining at least one value for a quantity indicative of the end capillary blood CO2 content of the subject, the determination of the value being carried out in a time period less than that required for blood leaving the lungs of the subject to pass through the circulatory system of the subject and return to the lungs, the determination of the value using the CO2 concentration of the breathing gases exhaled for the second breathing condition; (h) performing a regression analysis using the determined VCO21, VCO22, and end capillary blood CO2 quantity values to establish a regression line; (i) extrapolating the regression line to obtain a value for the end capillary blood CO2 quantity when the amount of CO2 released from the circulatory system of the subject (VCO2) is zero; determining a further value for the quantity indicative of the end capillary blood CO2 content for breathing of the subject in the first breathing condition; forming a relationship between the value for the quantity indicative of the end capillary blood CO2 content for breathing in the first breathing condition used in the regression analysis and the value obtained by extrapolating the regression line in step (i); and applying the relationship to the further determined value for a quantity indicative of the end capillary blood CO2 content to provide a new value for the value which was obtained by the extrapolation of the regression line in step (i). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A method for determining a change in a measured condition of the circulatory system of a subject, said method comprising the steps of:
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(a) non-invasively obtaining, from the subject, an initial value for at least one selected variable comprising at least one of exhaled CO2 amount, end tidal CO2 amount, heart rate, and the amount of CO2 released from the circulatory system of the subject (VCO2); (b) carrying out a discrete measurement of a circulatory system condition of a subject; (c) obtaining a further value for the at least one selected variable subsequent to carrying out the discrete measurement; (d) comparing the further value of the variable with the initial value of said variable to determine whether the obtained variable has changed in value; and (e) initiating a carrying out of a further discrete measurement of a circulatory system condition of the subject responsive to a change in the value of the variable. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56)
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57. Apparatus for determining a change in a measured condition of the circulatory system of a subject, said apparatus comprising:
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(a) means for non-invasively obtaining, from the subject, an initial value and subsequent value for at least one selected selected variable comprising at least one of exhaled CO2 amount, end tidal CO2 amount, heart rate, and the amount of CO2 released from the circulatory system of the subject (VCO2); (b) means for carrying out a discrete measurement of a circulatory system condition of a subject; (c) means for comparing the subsequent value of the variable with the initial value of said variable to determine whether the obtained variable has changed in value and for causing said means for carrying out a discrete measurement to carry out a further discrete measurement of a circulatory system condition of the subject responsive to a change in the value of the variable. - View Dependent Claims (58, 59, 60, 61, 62, 63)
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Specification