US 7,072,701 B2 · Method for spectrophotometric blood oxygenation monitoring

Abstract

A method and apparatus for non-invasively determining the blood oxygen saturation level within a subject's tissue is provided that utilizes a near infrared spectrophotometric (NIRS) sensor capable of transmitting a light signal into the tissue of a subject and sensing the light signal once it has passed through the tissue via transmittance or reflectance. The method includes the steps of: (1) transmitting a light signal into the subject's tissue, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; (2) sensing a first intensity and a second intensity of the light signal, along the first, second, and third wavelengths after the light signal travels through the subject at a first and second predetermined distance; (3) determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity of the first, second, and third wavelengths; (4) determining a difference in attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength; and (5) determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength.

Claims50

Dependent claims

A method for non-invasively determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor, said method comprising the steps of:

transmitting a light signal into the subject's tissue using the sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength;
sensing a first intensity and a second intensity of the light signal, using the sensor, along the first, second, and third wavelengths after the light signal travels through the subject at a first predetermined distance and a second predetermined distance;
wherein the sensor is calibrated using empirical data that relates to the subject's tissue that is sensed by the sensor to account for light signal attenuation resulting from light signal scattering within the subject's tissue;
determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity of the first, second, and third wavelengths;
determining a difference in attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength;
determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength.

3 more elements

A method for non-invasively determining a concentration of oxyhemoglobin and a concentration of deoxyhemoglobin within a subject's tissue using a near infrared spectrophotometric sensor, said method comprising the steps of:

(a) determining a blood oxygen saturation level with the subject's tissue by
transmitting a light signal into the subject's tissue from a NIRS sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength;
sensing a first intensity and a second intensity of the light signal, using the sensor, along the first, second, and third wavelengths after the light signal travels through the subject at a first and second predetermined distances;
wherein the sensor is calibrated using empirical data that relates to the subject's tissue that is sensed by the sensor to account for light signal attenuation resulting from light signal scattering within the subject's tissue;
determining an attenuation of the light signal for each of the first, second, and third wavelengths using the first intensity and the sensed second intensity of the first, second, and third wavelengths;
determining a difference in attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength;
determining a first calibration constant and a second calibration constant using empirical data developed from the subject at or about the same time as when the sensing occurs;
determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength, and the first calibration constant and the second calibration constant;
(b) determining a photon pathlength Lb, and
(c) determining the concentration of oxyhemoglobin and the concentration of deoxyhemoglobin within the subject's tissue using the first and second calibration constants.

7 more elements

A method for non-invasively determining a concentration of oxyhemoglobin and a concentration of deoxyhemoglobin within a subject's tissue at an initial time t1 and a subsequent time t2 using a near infrared spectrophotometric sensor, said method comprising the steps of:

(a) determining a blood oxygen saturation level with the subject's tissue by
transmitting a light signal into the subject's tissue from a NIRS sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength;
sensing a first intensity and a second intensity of the light signal, using the sensor, along the first, second, and third wavelengths after the light signal travels through the subject at a first and second predetermined distances;
wherein the sensor is calibrated using empirical data that relates to the subject's tissue that is sensed by the sensor to account for light signal attenuation resulting from light signal scattering within the subject's tissue;
determining an attenuation of the light signal for each of the first, second, and third wavelengths using the first intensity and the sensed second intensity of the first, second, and third wavelengths;
determining a difference in attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength;
determining a first calibration constant and a second calibration constant using empirical data developed from the subject at or about the same time as when the sensing occurs;
determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength, and the first calibration constant and the second calibration constant;
(b) determining a photon pathlength Lb;
(c) determining the concentration of oxyhemoglobin and the concentration of deoxyhemoglobin within the subject's tissue at the initial time t1 using the equation:
[
A
Hb
A
HbO
2
]
⁢
(
L
b
)
-
1
-
[
Ψ
Hb
Ψ
HbO
2
]
⁢
(
L
b
)
-
1
=
[
Hb
HbO
2
]
where ΨHbO2 represents the first calibration constant, ΨHb represents the second calibration constant, AHbO2 represents a difference in attenuation of light signal attributable to oxyhemoglobin, and AHb represents a difference in attenuation of light signal attributable to deoxyhemoglobin;
and
(d) determining a change in the concentration of oxyhemoglobin and a change in the concentration of deoxyhemoglobin from the initial time t1 to a subsequent second time t2, determined using the equation:
[
-
log
⁡
(
I
t2
I
t1
)
λ1
/
L
λ1
-
log
⁡
(
I
t2
I
t1
)
λ2
/
L
λ2
-
log
⁡
(
I
t2
I
t1
)
λ3
/
L
λ3
]
=
[
α
Hb
⁢
⁢
λ1
α
HbO
2
⁢
λ1
α
Hb
⁢
⁢
λ2
α
HbO
2
⁢
λ2
α
Hb
⁢
⁢
λ3
α
HbO
2
⁢
λ3
]
*
[
Δ
⁢
⁢
Hb
Δ
⁢
⁢
HbO
2
]
;
and
(e) determining the concentration of oxyhemoglobin and the concentration of deoxyhemoglobin within the subject's tissue at the subsequent time t2 using the equations:
[Hb]t2=ΔHb(t2)+[Hb]t1 and
[HbO2]t2=ΔHbO2(t2)+[HbO2]t1.

136 more elements

A method for non-invasively determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor, said method comprising the steps of:

transmitting a light signal into the subject's tissue using the sensor, wherein the transmitted light signal includes a first wavelength, and a second wavelength;
sensing a first intensity and a second intensity of the light signal, using the sensor, along the first wavelength, after the light signal travels through the subject at a first and a second predetermined distances;
sensing a third intensity and a fourth intensity of the light signal, using the sensor, along the second wavelength, after the light signal travels through the subject at said first and said second predetermined distances;
wherein the sensor is calibrated using empirical data that relates to the subject's tissue that is sensed by the sensor to account for light signal attenuation resulting from light signal scattering within the subject's tissue;
determining a first attenuation of the light signal for the first wavelength using said first intensity and said second intensity;
determining a second attenuation of the light signal for the second wavelength using said third intensity and said fourth intensity;
determining a ratio of said first and said second attenuations of the light signal for the first, and second wavelengths;
determining the blood oxygen saturation level within the subject's tissue using said ratio.

5 more elements

Dependencies are inferred from the claim text.

Method for spectrophotometric blood oxygenation monitoring

Life of this patent

Method for spectrophotometric blood oxygenation monitoring

Life of this patent

Abstract

Claims50