Hemometrix temperature compensation
First Claim
1. A method for determining a partial pressure of oxygen of blood at a predefined reference temperature of blood during an in vivo blood gas measurement, comprising the steps of:
- (a) measuring in vivo a partial pressure of oxygen of blood at an arbitrary temperature that is substantially different than the reference temperature of blood, as a function of a physical parameter that changes to indicate the partial pressure of oxygen of blood at a measurement site, said step of measuring including the steps of;
(i) producing a first signal indicative of the partial pressure of oxygen of blood, in response to changes in the physical parameter;
(ii) producing a second signal indicative of the arbitrary temperature of blood at the measurement site; and
(iii) processing the first signal to determine the partial pressure of oxygen of blood at the arbitrary temperature;
(b) determining an estimate of a partial pressure of oxygen of blood at the predefined reference temperature of blood as a function of the partial pressure of oxygen of blood at the arbitrary temperature of blood, and of the second signal;
(c) determining a more accurate estimate of the partial pressure of oxygen of blood at the predefined reference temperature as a function of;
(i) the partial pressure of oxygen of blood at the arbitrary temperature of blood;
(ii) the second signal; and
(iii) the estimate of the partial pressure of oxygen of blood at the predefined reference temperature; and
(d) iteratively repeating step (c), each iteration using said more accurate estimate of the partial of oxygen of blood from a previous iteration as a value for said estimate in (c)(iii), until a predefined number of such iterations have been completed, a more accurate estimate that results from a last of such iterations approximating the partial pressure of oxygen of blood at the predefined reference temperature corresponding to the measurement of the partial pressure of oxygen of blood made at the arbitrary temperature of blood.
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Accused Products
Abstract
A method for converting a value for the partial pressure of oxygen (pO2) in blood at a measurement temperature to a corresponding value at a reference temperature (37° C.). A value for pO2 is determined by measurements made in a patient'"'"'s blood stream using a phosphorescent compound that is sensitive to the concentration of oxygen. The phosphorescent compound is illuminated with a short pulse of light, causing it to produce a phosphorescent emission having a rate of decay that varies as the function of the partial pressure of oxygen in the blood surrounding the phosphorescent compound. A detector produces an electrical signal corresponding to the intensity of the phosphorescent emission, and the electrical signal is converted to a corresponding digital value for input to a microcomputer. Also supplied to the microcomputer in digital form is a signal indicative of the temperature at the measurement site where the phosphorescent compound is disposed. The microcomputer determines the phosphorescent decay rate and from that value, determines the pO2 at the measurement site for the temperature at which the measurement was made. An initial estimate of a corresponding value for pO2 at the reference temperature is made as a function of the measurement temperature and the pO2 at that temperature. A more accurate estimate of pO2 at the reference temperature is iteratively determined by successively evaluating an expression that is a function of the initial measurement and a previous more accurate estimate. If the measurement temperature is less than the reference temperature, the current more accurate estimate is replaced by the average of the previous two estimates. A final more accurate estimate representing the value for pO2 at the reference temperature is then displayed.
38 Citations
20 Claims
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1. A method for determining a partial pressure of oxygen of blood at a predefined reference temperature of blood during an in vivo blood gas measurement, comprising the steps of:
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(a) measuring in vivo a partial pressure of oxygen of blood at an arbitrary temperature that is substantially different than the reference temperature of blood, as a function of a physical parameter that changes to indicate the partial pressure of oxygen of blood at a measurement site, said step of measuring including the steps of; (i) producing a first signal indicative of the partial pressure of oxygen of blood, in response to changes in the physical parameter; (ii) producing a second signal indicative of the arbitrary temperature of blood at the measurement site; and (iii) processing the first signal to determine the partial pressure of oxygen of blood at the arbitrary temperature; (b) determining an estimate of a partial pressure of oxygen of blood at the predefined reference temperature of blood as a function of the partial pressure of oxygen of blood at the arbitrary temperature of blood, and of the second signal; (c) determining a more accurate estimate of the partial pressure of oxygen of blood at the predefined reference temperature as a function of; (i) the partial pressure of oxygen of blood at the arbitrary temperature of blood; (ii) the second signal; and (iii) the estimate of the partial pressure of oxygen of blood at the predefined reference temperature; and (d) iteratively repeating step (c), each iteration using said more accurate estimate of the partial of oxygen of blood from a previous iteration as a value for said estimate in (c)(iii), until a predefined number of such iterations have been completed, a more accurate estimate that results from a last of such iterations approximating the partial pressure of oxygen of blood at the predefined reference temperature corresponding to the measurement of the partial pressure of oxygen of blood made at the arbitrary temperature of blood. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for determining a partial pressure of oxygen in a patient'"'"'s blood, at a predefined reference temperature, comprising the steps of:
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(a) transmitting a light signal to a measurement site in the patient'"'"'s body, said light signal causing a material sensitive to the light signal to emit a return light signal having a parameter that varies as a function of the partial pressure of oxygen that is present in the blood at the measurement site; (b) detecting the return light signal, producing an electrical signal corresponding thereto, said electrical signal being indicative of the partial pressure of oxygen at a temperature of the blood at the measurement site; (c) producing a temperature signal indicative of the temperature of the blood at the measurement site at the time the return light signal is produced, said temperature being substantially different that the reference temperature; (d) digitizing the temperature signal and the electrical signal; (e) determining an estimate of a partial pressure of oxygen at the predefined reference temperature as a function of the digitized electrical signal, which represents the partial pressure of oxygen at the temperature of blood at the measurement site, and as a function of the digitized temperature at the measurement site; (f) determining a more accurate estimate of the partial pressure of oxygen at the predefined reference temperature as a function of; (i) the digitized electrical signal; (ii) the digitized temperature at the measurement site; and (iii) the estimate of the partial pressure of oxygen at the predefined reference temperature; and (g) iteratively repeating step (f), each iteration using said more accurate estimate of the partial pressure of oxygen from a previous iteration as a value for said estimate in (f)(iii), until a predefined number of such iterations have been completed, a more accurate estimate that results from a last of such iterations approximating the partial pressure of oxygen at the predefined reference temperature corresponding to the measurement of the partial pressure of oxygen made at the temperature of blood at the measurement site. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A method for determining a partial pressure of oxygen at a predefined reference temperature at a measurement site disposed on a distal end of an optical fiber within a patient'"'"'s cardiovascular system, a temperature at said measurement site being substantially different than the reference temperature, comprising the steps of:
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(a) conveying a pulse of light through the optical fiber toward its distal end, said light exciting a phosphorescent material disposed on the distal end of the optical fiber into phosphorescence that is quenched at a rate dependent upon the partial pressure of oxygen at the measurement site, producing a return light signal that travels through the optical fiber; (b) determining a decay time for the return light signal, and based upon the decay time, the partial pressure of oxygen at the measurement site at the temperature of the measurement site; (c) sensing the temperature of the measurement site, producing a temperature signal indicative of said temperature; (d) determining a first estimate of the partial pressure of oxygen at the predefined reference temperature as a function of the partial pressure of oxygen that was determined from the decay time and as a function of the temperature signal; (e) determining a more accurate estimate of the partial pressure of oxygen at the predefined reference temperature as a function of; (i) the partial pressure of oxygen that was determined from the decay time; (ii) the temperature signal; and (iii) the first estimate of the partial pressure of oxygen at the predefined reference temperature; and (f) iteratively repeating step (e), a first such iteration substituting the more accurate estimate of the partial pressure of oxygen at the predefined reference temperature for the first estimate of step (e)(iii), and a subsequent iteration substituting the more accurate estimate of the partial pressure of oxygen determined from the previous iteration for the value previously used in step (e)(iii) in the iteration before, the more accurate estimate from the last of a predefined number of such iterations closely approximating the partial pressure of oxygen at the predefined reference temperature. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification