Method for non-invasive spectrophotometric blood oxygenation monitoring

Claim 1

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 at a predetermined first intensity using the sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing 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; 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 predetermined 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 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.

Claim 2

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 at a predetermined first intensity using the sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing 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; 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 predetermined 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 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.

Claim 15

A method for determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor attached to the skin of the subject, said method comprising the steps of: transmitting a light signal into the subject's tissue at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject; determining an attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined 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.

Claim 16

A method for determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor attached to the skin of the subject, said method comprising the steps of: transmitting a light signal into the subject's tissue at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject; determining an attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined 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.

Claim 32

A method for calibrating a near infrared spectrophotometric sensor for use in determining the blood oxygen saturation level within a subject's tissue, said method comprising the steps of: transmitting a light signal into the subject's tissue at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject; determining an attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined 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; and calibrating the sensor using the first calibration constant and the second calibration constant.

Claim 33

A method for calibrating a near infrared spectrophotometric sensor for use in determining the blood oxygen saturation level within a subject's tissue, said method comprising the steps of: transmitting a light signal into the subject's tissue at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject; determining an attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined 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; and calibrating the sensor using the first calibration constant and the second calibration constant.

Claim 40

A method for calibrating a NIRS sensor, said method comprising the steps of: transmitting a light signal from a calibrated NIRS sensor into a reference sample at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal with the calibrated NIRS sensor along the first, second, and third wavelengths after the light signal travels through the reference sample; determining a first attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined first intensity and the second intensity of the light signal sensed with the calibrated NIRS sensor; transmitting a light signal from an uncalibrated second NIRS sensor into the reference sample at the predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal with the uncalibrated second NIRS sensor along the first, second, and third wavelengths after the light signal travels through the subject; determining a second attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined first intensity and the second intensity of the first, second, and third wavelengths sensed with the uncalibrated second NIRS sensor; adjusting the uncalibrated second NIRS sensor so that the second attenuation substantially agrees with the first attenuation.

Claim 41

A method for calibrating a NIRS sensor, said method comprising the steps of: transmitting a light signal from a calibrated NIRS sensor into a reference sample at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal with the calibrated NIRS sensor along the first, second, and third wavelengths after the light signal travels through the reference sample; determining a first attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined first intensity and the second intensity of the light signal sensed with the calibrated NIRS sensor; transmitting a light signal from an uncalibrated second NIRS sensor into the reference sample at the predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal with the uncalibrated second NIRS sensor along the first, second, and third wavelengths after the light signal travels through the subject; determining a second attenuation of the light signal for each of the first, second, and third wavelengths using the predetermined first intensity and the second intensity of the first, second, and third wavelengths sensed with the uncalibrated second NIRS sensor; adjusting the uncalibrated second NIRS sensor so that the second attenuation substantially agrees with the first attenuation.

Claim 42

A method for determining a blood oxygen saturation level within a subject's tissue attributable to venous blood, said method comprising the steps of: providing a NIRS sensor for sensing the subject's tissue; determining a blood oxygen saturation level with the subject's tissue using the NIRS sensor: determining a blood oxygen saturation level attributable to arterial blood within the subject's tissue using a pulse oximetry technique; and determining a blood oxygen saturation level attributable to venous blood within the subject's tissue using the equation: SvO 2 = CrSO 2 - ( Ka * SpO 2 ) Kv .

Claim 43

A method for determining a blood oxygen saturation level within a subject's tissue attributable to venous blood, said method comprising the steps of: providing a NIRS sensor for sensing the subject's tissue; determining a blood oxygen saturation level with the subject's tissue using the NIRS sensor: determining a blood oxygen saturation level attributable to arterial blood within the subject's tissue using a pulse oximetry technique; and determining a blood oxygen saturation level attributable to venous blood within the subject's tissue using the equation: SvO 2 = CrSO 2 - ( Ka * SpO 2 ) Kv .

Claim 45

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 at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject using the sensor; 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 predetermined 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 d*B; and (c) determining the concentration of oxyhemoglobin and the concentration of deoxyhemoglobin within the subject's tissue using the first and second calibration constants.

Claim 46

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 at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject using the sensor; 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 predetermined 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 d*B; and (c) determining the concentration of oxyhemoglobin and the concentration of deoxyhemoglobin within the subject's tissue using the first and second calibration constants.

Claim 48

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 at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject using the sensor; 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 predetermined 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 d*B; (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 ]  ( dB ) - 1 - [ Ψ Hb Ψ HbO 2 ]  ( dB ) - 1 = [ Hb HbO 2 ] t1 where Ψ HbO2 represents the first calibration constant, Ψ Hb represents the second calibration constant, A HbO2 represents a difference in attenuation of light signal attributable to oxyhemoglobin, and A Hb 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 are determined using the equation: [ - log   ( I t2 / I t1 ) λ  1 / ( d * B λ  1 ) - log   ( I t2 / I t1 ) λ  2 / ( d * B λ  2 ) - log   ( I t2 / I t1 ) λ  3 / ( d * B λ  3 ) ] = [ α Hb   λ  1 α HbO 2  λ  1 α Hb   λ  2 α HbO 2  λ  2 α Hb   λ  3 α HbO 2  λ  3 ] * [ ΔHb ΔHbO 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 ( t 2 )+[ Hb] t1 and [ HbO 2 ] t2 =ΔHbO 2 ( t 2 )+[ HbO 2 ] t1 .

Claim 49

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 at a predetermined first intensity, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a second intensity of the light signal along the first, second, and third wavelengths after the light signal travels through the subject using the sensor; 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 predetermined 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 d*B; (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 ]  ( dB ) - 1 - [ Ψ Hb Ψ HbO 2 ]  ( dB ) - 1 = [ Hb HbO 2 ] t1 where Ψ HbO2 represents the first calibration constant, Ψ Hb represents the second calibration constant, A HbO2 represents a difference in attenuation of light signal attributable to oxyhemoglobin, and A Hb 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 are determined using the equation: [ - log   ( I t2 / I t1 ) λ  1 / ( d * B λ  1 ) - log   ( I t2 / I t1 ) λ  2 / ( d * B λ  2 ) - log   ( I t2 / I t1 ) λ  3 / ( d * B λ  3 ) ] = [ α Hb   λ  1 α HbO 2  λ  1 α Hb   λ  2 α HbO 2  λ  2 α Hb   λ  3 α HbO 2  λ  3 ] * [ ΔHb ΔHbO 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 ( t 2 )+[ Hb] t1 and [ HbO 2 ] t2 =ΔHbO 2 ( t 2 )+[ HbO 2 ] t1 .

Claim 50

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 at a predetermined first intensity using the sensor; sensing a second intensity of the light signal along three or more selectively chosen wavelengths after the light signal travels through the subject using the sensor; 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 at least “n” number of the selectively chosen wavelengths using the predetermined first intensity and the sensed second intensity of the selectively chosen wavelengths, where “n” is an integer equal to or greater than three; determining a difference in attenuation of the light signal between a first wavelength and each of “n” number of the selectively chosen wavelengths; determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and each of the “n” number of other selectively chosen wavelengths.

Claim 51

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 at a predetermined first intensity using the sensor; sensing a second intensity of the light signal along three or more selectively chosen wavelengths after the light signal travels through the subject using the sensor; 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 at least “n” number of the selectively chosen wavelengths using the predetermined first intensity and the sensed second intensity of the selectively chosen wavelengths, where “n” is an integer equal to or greater than three; determining a difference in attenuation of the light signal between a first wavelength and each of “n” number of the selectively chosen wavelengths; determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and each of the “n” number of other selectively chosen wavelengths.

Claim 52

A method for determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor attached to the skin of the subject, said method comprising the steps of: transmitting a light signal into the subject's tissue at a predetermined first intensity; sensing a second intensity of the light signal along three or more selectively chosen wavelengths after the light signal travels through the subject; determining an attenuation of the light signal for at least “n” number of the selectively chosen wavelengths using the predetermined first intensity and the sensed second intensity of the selectively chosen wavelengths, where “n” is an integer equal to or greater than three; determining a difference in attenuation of the light signal between a first wavelength and each of “n” number of the selectively chosen wavelengths; 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 each of “n” number of the selectively chosen wavelengths, and the first calibration constant and the second calibration constant.

Claim 53

A method for determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor attached to the skin of the subject, said method comprising the steps of: transmitting a light signal into the subject's tissue at a predetermined first intensity; sensing a second intensity of the light signal along three or more selectively chosen wavelengths after the light signal travels through the subject; determining an attenuation of the light signal for at least “n” number of the selectively chosen wavelengths using the predetermined first intensity and the sensed second intensity of the selectively chosen wavelengths, where “n” is an integer equal to or greater than three; determining a difference in attenuation of the light signal between a first wavelength and each of “n” number of the selectively chosen wavelengths; 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 each of “n” number of the selectively chosen wavelengths, and the first calibration constant and the second calibration constant.