Apparatus and method for monitoring respiration with a pulse oximeter
First Claim
1. A method for monitoring a patient'"'"'s respiration through changes in the patient'"'"'s blood concentrations, said method comprising the steps of:
- monitoring a portion of perfused tissue to obtain at least one plethysmographic signal;
processing said at least one plethysmographic signal to obtain pulsatile AC signal component information and substantially non-pulsatile DC signal component information, wherein said non-pulsatile DC signal component information reflects a variability separate from a pulse of a patient;
determining a relative concentration of arterial blood and venous blood in said tissue based on said DC signal component information; and
monitoring said relative concentration of arterial and venous blood based on said DC signal component information over time to determine a respiration frequency from increases and decreases in said relative concentration.
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Abstract
An apparatus and method for monitoring a secondary physiological process through variations caused by the secondary process in an optical signal used to calculate values related to blood oxygen levels. In particular, the optical signal may be divided into distinct portions such that a portion more directly affected by a particular secondary physiological process may be isolated and the secondary physiological process monitored. The apparatus and method is particularly useful for photoplethysmographically monitoring a patient'"'"'s respiration frequency through changes in relative concentrations of blood oxygen related values that are proportionally related to the amounts of venous and arterial blood in a portion of tissue.
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Citations
22 Claims
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1. A method for monitoring a patient'"'"'s respiration through changes in the patient'"'"'s blood concentrations, said method comprising the steps of:
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monitoring a portion of perfused tissue to obtain at least one plethysmographic signal;
processing said at least one plethysmographic signal to obtain pulsatile AC signal component information and substantially non-pulsatile DC signal component information, wherein said non-pulsatile DC signal component information reflects a variability separate from a pulse of a patient;
determining a relative concentration of arterial blood and venous blood in said tissue based on said DC signal component information; and
monitoring said relative concentration of arterial and venous blood based on said DC signal component information over time to determine a respiration frequency from increases and decreases in said relative concentration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 22)
applying electromagnetic radiation of at least two wavelengths to said portion of tissue;
detecting signals for each said wavelength applied to said portion of tissue; and
obtaining said substantially non-pulsatile DC signal component information for each of said at least two wavelengths.
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5. The method of claim 1, wherein said step of determining a relative concentration further comprises:
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determining a first quantitative value associated with arterial blood in said tissue; and
determining a second quantitative value associated with venous blood in said tissue.
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6. The method of claim 5, wherein said first quantitative value is associated with oxygenated hemoglobin (HbO2) and said second quantitative value is associated with de-oxygenated hemoglobin (Hb).
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7. The method of claim, 6 wherein said relative concentration is a ratio HbO2/Hb of said oxygenated hemoglobin and said de-oxygenated hemoglobin.
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8. The method of claim 7 wherein said ratio is calculated using the following:
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wherein, ε
1Hb and ε
2Hb represent extinction coefficients of said de-oxygenated hemoglobin for a first and second wavelengths of said signal plethysmographic, respectively, and ε
1HbO2 and ε
2HbO2 represent extinction coefficients of said oxygenated hemoglobin for said first and second wavelengths of said plethysmographic signal, respectively, and R represent the ratio of ration for said plethysmographic signal.
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9. The method of claim 1, wherein said relative concentration is monitored for said variations over a frequency range of 0 to 1.5 hertz.
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22. The method of claim, 7 wherein said relative concentration is a ratio, HbO2/Hb, of said of oxygenated hemoglobin and said de-oxygenated hemoglobin.
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10. An apparatus for monitoring respiration, using optical signals to identify changes in values related to blood oxygen levels caused by said respiration, said apparatus comprising:
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at least a first emitter for controllably emitting at least first and second wavelengths of electromagnetic radiation to a portion of living tissue;
a detector for detecting signals relative to said emitted first and second wavelengths of said electromagnetic radiation and producing a detector signal indicative thereof; and
a processor operable to receive said detector signal, said processor further operable for;
processing said detector signal to obtain pulsatile AC signal component information and substantially invariant DC signal component information; and
using said DC signal component information to determine a quantitative value related to a ratio of arterial blood to venous blood of said tissue, wherein said non-pulsatile DC signal component information reflects a variability separate from a pulse of a patient;
monitoring said value to determine variations in said ratio over a predetermined frequency range indicative of respiration; and
generating an output signal indicative of respiration. - View Dependent Claims (11, 12, 13, 14, 15, 16)
wherein, ε
1Hb and ε
2Hb represent extinction coefficients of said de-oxygenated hemoglobin for a first and second wavelengths of said plethysmographic signal, respectively, and ε
1HbO2 and ε
2HbO2 represent extinction coefficients of said oxygenated hemoglobin for said first and second wavelengths of said plethysmographic signal, respectively, and R represent the ratio of ration for said plethysmographic signal.
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17. A method for monitoring a patient'"'"'s respiration through changes in the patient'"'"'s blood concentrations, said method comprising the steps of:
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applying first and second optical signals to a portion of tissue, wherein said first and second optical signals have different wavelengths;
detecting said first and second optical signals as modulated by said tissue and generating a detector signal representative of said first and second optical signals;
processing said detector signal to obtain first and second DC signal components corresponding with said first and second optical signals;
determining a relative concentration of arterial and venous blood in said tissue based on said first and second DC signal components; and
monitoring said relative concentration to identify a variation associated with respiration. - View Dependent Claims (18, 19, 20, 21)
determining a first quantitative value associated with arterial blood in said tissue; and
determining a second quantitative value associated with venous blood in said tissue.
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21. The method of claim 20, wherein said first quantitative value is associated with oxygenated hemoglobin (HbO2) and said second quantitative value is associated with de-oxygenated hemoglobin (Hb).
Specification