WO2019026062A1 - Procédé de mesure de la saturation en oxygène du sang artériel et appareil à cet effet - Google Patents

Procédé de mesure de la saturation en oxygène du sang artériel et appareil à cet effet Download PDF

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WO2019026062A1
WO2019026062A1 PCT/IL2018/050827 IL2018050827W WO2019026062A1 WO 2019026062 A1 WO2019026062 A1 WO 2019026062A1 IL 2018050827 W IL2018050827 W IL 2018050827W WO 2019026062 A1 WO2019026062 A1 WO 2019026062A1
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light
wavelength
tissue
wavelengths
intensity
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Meir Nitzan
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Jerusalem College of Tech
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue
    • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
    • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
    • A61B5/14552—Details of sensors specially adapted therefor
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6813—Specially adapted to be attached to a specific body part
    • A61B5/6825—Hand
    • A61B5/6826—Finger
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2560/00—Constructional details of operational features of apparatus; Accessories for medical measuring apparatus
    • A61B2560/02—Operational features
    • A61B2560/0223—Operational features of calibration, e.g. protocols for calibrating sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0233—Special features of optical sensors or probes classified in A61B5/00
    • A61B2562/0238—Optical sensor arrangements for performing transmission measurements on body tissue
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/026—Measuring blood flow
    • A61B5/029—Measuring blood output from the heart, e.g. minute volume
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/08—Measuring devices for evaluating the respiratory organs

Definitions

  • the presently disclosed subject matter relates to a method for oxygen saturation measurement in arterial blood and an apparatus therefor
  • Oxygen saturation in blood is the ratio between the concentration of oxygenated hemoglobin and total hemoglobin in the blood.
  • the value of oxygen saturation in arterial blood, Sa0 2 provides information regarding the performance of the respiratory system.
  • Total hemoglobin in the blood includes oxygenated hemoglobin (Hb0 2 ) and deoxygenated hemoglobin (Hb).
  • Pulse oximetry is a noninvasive method for the assessment of Sa0 2 by measuring the cardiac induced changes in light transmission through the tissue due to changes in the blood volume of small arteries in the microcirculation, which is known as photoplethy smography (PPG).
  • Pulse oximetry technique is based on the different light absorption spectra for Hb0 2 and Hb (Fig. 1), and on the measurement of light transmission changes in two wavelengths, which, in the commercial devices, are in the red and the infra-red (IR) regions (Farmer 1997, Wieben 1997, Moyle 2002).
  • the quantitative relationship between the PPG pulses and the Sa0 2 is derived by applying the modified Beer- Lambert equation to the transmitted light intensity, , through a tissue sample of width d which includes blood vessels, arteries and veins, with whole blood (Matcher 2002, Delpy 1988, Yoxal 1997).
  • the transmitted light intensity, I t c ⁇ m thus be expressed as:
  • Pulse oximetry is based on the application of Equation [la] to the PPG signal, by substituting for l t the values of Is, which represents the lower light transmission through the higher tissue blood volume during systole, and ID, which represents the higher transmitted light through the lower tissue blood volume at end-diastole (as shown in Fig. 2). Further assuming that the attenuation G does not change appreciably by the systolic arterial blood volume increase (Matcher 2002, Yoxal et al 1997), it can be shown that: and
  • ID-IS is the PPG signal amplitude (AM) shown in Fig. 2, and is related to the maximal blood volume change during systole (Babchenko et al 2001).
  • the pulse oximetry technique for the assessment of oxygen saturation in arterial blood is based on the assumption that the PPG signal reflects absorption in the arterial blood volume increase during systole. It should be noted that pulse oximetry is a measurement in microcirculation and its accuracy is reduced if the illuminated region includes a big artery (Mannheimer et al 2004, Reuss and Siker 2004).
  • ratios R defined by:
  • ⁇ 2 assuming that the difference in the blood concentration change AC between the two wavelengths and the difference in path-lengths between the two wavelengths can be neglected ( ⁇ , h ⁇ h).
  • the assumption that the illuminated tissue is the same for the two wavelengths seems to be valid for transmission PPG in the finger, but may be inaccurate in reflection PPG where the penetration depth for the two wavelengths may be different.
  • the assumption that the difference in path-lengths can be neglected can be acceptable when the two wavelengths are close to each other (i.e. when both are in the IR region) but not for wavelengths in the red and IR regions.
  • Equation [5] If Equation [5] is valid, the relationship between the measured parameter R and the physiological parameter Sa0 2 can be derived Nitzan et al 2000): (6a)
  • ⁇ and SD are the extinction coefficients for Hb0 2 and Hb, respectively and the subscripts 1 and 2 refer to the two wavelengths.
  • the assumption that h is not much different than h, and R can be approximated by ⁇ / ⁇ 2 can introduce error in the calculation of Sa0 2 : significant error for wavelengths in the red and IR regions and small error for two wavelengths in the IR region. In the latter case, some correction, due to the small difference between the two path-lengths, may be required (Nitzan et al 2000):
  • the maximum (ID), minimum (Is), amplitude and relative amplitude (rAM-AM/Is) are calculated (Fig. 2), and from the relative amplitude in the two wavelengths, rAMi and
  • the measured parameter R is a
  • Sa0 2 in commercial pulse oximeters which are on red and infrared light can be derived from R by means of in vitro calibration: blood is extracted from an artery and its oxygen saturation value is determined by arterial blood gas (ABG) test or by co-oximetry. As explained above the method requires calibration because of the difference in light scattering by tissue and blood between these wavelengths.
  • ABSG arterial blood gas
  • the accuracy of Sa0 2 measurement by pulse oximetry is not high, and is designated by Sp0 2 .
  • Sp0 2 accuracy is obtained by comparing Sp02 measurement to Sa0 2 measurement in extracted arterial blood by means of CO-oximeter, which is the gold-standard for Sa0 2 measurements.
  • the accuracy of Sp0 2 as declared by the manufacturers is 2%, say the standard-deviation of the Sp0 2 and CO-oximeter measurements is 2%, which means that for 5% of the examinations the deviation from the gold-standard is 4% (two standard-deviations). For Sa0 2 values below 80%, the accuracy is even lower.
  • invasive Sa02 measurement is often used instead of noninvasive Sp02 measurement.
  • maintaining a minimum Sp0 2 level of 94% or 96% in mechanically ventilated patients has been proposed, in order to ensure a minimal Sa0 2 value of 90%.
  • the limited ability of pulse oximetry to accurately determine the level of excess oxygenation is particularly important for preterm newborns receiving supplemental oxygen, due to their vulnerability to retinopathy of prematurity, induced by high oxygen partial pressure in the arterial blood.
  • the significance of accurate Sp0 2 measurement was demonstrated in three studies, SUPPORT, BOOST II and COT studies, where 4911 preterm newborns receiving oxygen supplementation were randomized to either a low (85-89%) or high (91-95%) Sp0 2 value. Increased risk of mortality was noted in the first group while an increased incidence of retinopathy of prematurity was found in the second group.
  • the authors of the meta-analysis of those studies recommend that Sp0 2 should be targeted at 90-95% in infants with gestational age ⁇ 28 weeks. Some authors suggest that pulse oximetry should not be the sole means for monitoring oxygenation in the neonatal ICU.
  • Equation (6a or 6b) The low accuracy of Sp0 2 measurement partly originates from the requirement for calibration.
  • Equation (6a or 6b) the derivation of the oxygen saturation Sa0 2 from the measured ratio R cannot be achieved directly from Equation (6a or 6b), together with the values of the extinction coefficients for oxygenated blood, ⁇ 0 , and for deoxygenated blood, Sd, because h and h are not equal, due to the different effective optical path-length of the two wavelengths.
  • Equation (6b) thus cannot be used because / 2 //i is not known.
  • the calibration process assumes constant value of / 2 //i for all persons undergoing examination, independent on the clinical variables, which is not always the case.
  • the effects of the difference in path-length between the two wavelengths, caused by the different attenuation of each of the wavelengths, can be reduced, if the two wavelengths are chosen close to one another, instead of in red and infrared. Accordingly, when two wavelengths in the infrared are chosen, the relative difference between the path- length of the first wavelength h and the path-length of the first wavelength h [say, (h- is about 3% (obtained by estimating h and h value from published data, Nitzan et al. 2000).
  • the two-infrared wavelengths pulse oximetry provides Sp0 2 value by using Equation (6b) and estimating the value of / 2 //i in Equation (6b) by a suitable correction factor.
  • the correction factor can be derived either by published data of h and h, or by comparing mean Sp0 2 value obtained, in multiple examinations, by the two-infrared wavelengths pulse oximetry to mean Sp0 2 value obtained by red-infrared pulse oximetry, that underwent extracted- blood calibration.
  • the accuracy of the individual Sp02 examinations in red- infrared pulse oximetry is low, about 4% in adults, the mean Sp02 value obtained by red- infrared pulse oximetry is expected to accurately reflect the mean of the corresponding Sp02 values.
  • the low accuracy of the individual Sp02 examinations in red-infrared pulse oximetry is partly attributed to the variability in the relative difference between h and h, which is about 10% for two wavelengths in red and infrared.
  • the technique requires the use of the values of the extinction coefficients of oxygenated and deoxygenated hemoglobin for the two wavelengths. These values were determined in several studies, using light absorption measurement in hemolyzed red blood cells (in order to eliminate the effect of scattering by the red blood cells in blood). The measurement of hemoglobin extinction coefficient in hemolyzed red blood cells is subject to errors, resulting in different curves of extinction coefficient vs. light wavelength in different studies. (Kim and Liu 2007, Nitzan et al 2013).
  • pulse oximetry is based on the difference between the spectrum of extinction coefficient (specific absorption coefficient) of Hb0 2 and that of Hb ( Figure 1).
  • the conventional pulse oximeter uses wavelengths in the red region and in the infrared region, the latter is above the isosbestic point, i.e. the point where Hb and Hb0 2 have equal extinction coefficients.
  • the Hb extinction coefficient is much higher than Hb0 2 extinction coefficient, while for wavelength above 700 nm the difference between Hb and Hb0 2 is moderate.
  • the Hb0 2 extinction coefficient is higher than that of Hb.
  • the conventional pulse oximeters use a wavelength in the red region, where the difference between Hb and Hb0 2 is high, and a wavelength in the infrared region, above the isosbestic point where the difference between the extinction coefficients is moderate.
  • the selection of this pair of wavelengths render great difference in path- length between the two wavelengths and require calibration for each type of pair of light- sources during manufacturing.
  • the calibration brings about significant measurement error because it is based on the assumption that the ratio of the path-lengths for the two wavelengths is equal for all examinees.
  • the relatively small difference between the two wavelengths results in relatively small difference in the path-length, reducing thereby the effect of path-length variability on Sp0 2 measurement between different persons and between different physiological and clinical situations. It is however preferable to choose the two wavelengths below and above the isosbestic point, such that the difference between the extinction coefficients of between Hb and Hb0 2 is high, in order to increase the signal.
  • a potential error in the pulse oximetry measurements is related to dependence of the emitted light wavelength on the temperature of the pulse oximeter light source.
  • the preferable light source is dual light emitting diode (LED), alternately emitting light in the two selected wavelengths.
  • the emitted spectrum of LED is broad (relative to laser light), generally 20-30 nm, and LED temperature difference between different examinations can affect peak wavelength and spectral width. There is therefore a need to reduce the effect of LED temperature difference between examinations on the emitted light wavelength spectrum.
  • Another potential error which originates from the broad LED spectrum, is related to dependence of the wavelength of the light, transmitted through the tissue, on the amounts of oxygenated and de-oxygenated hemoglobin through which the light has been passed.
  • Various trajectories of the photons passing through the tissue are shown in Figures 3 and 4.
  • the photons are emitted from the LED in relatively broad spectrum, having a width of 20-30 nm, and maintain the spectrum width when transmitted through the tissue in proximity of the emitting LED.
  • photons of different wavelength undergo different level of absorption and scattering.
  • the slope of the Hb0 2 extinction coefficient curve is much smaller than that of Hb, the spectrum change effect by absorption in Hb0 2 is not necessarily negligible relative to the spectrum change effect by absorption in Hb, because of the higher concentration of Hb0 2 , relative to Hb, in the finger.
  • the relative concentration of Hb0 2 in mixed venous blood is about 75%, the relative concentration of Hb0 2 in finger venous blood can reach 90% at high tissue temperature. In this case the relative concentration of Hb0 2 is 10 times higher than that of Hb.
  • photons of wavelength smaller than the peak wavelength undergo smaller absorption than photons of the peak wavelength for Hb0 2
  • the extinction coefficient is independent on the wavelength.
  • ⁇ is the extinction coefficient for the wavelength in the element
  • N is the number of photons emitted in the wavelength element
  • the effective change in the light wavelength spectrum depends on the effective path-length in the tissue, which increases with the thickness of tissue.
  • the effective path-length in the tissue can be estimated by measuring the intensity of the transmitted light, compared with the intensity of the emitted light, in one or several wavelengths.
  • the light spectrum can also change during its passage through the tissue due to scattering, both by the tissue and by the red blood cells, and due to absorption in melanin. As shown in Fig. 5, the scattering caused by the tissue and by the red blood and the absorption in melanin decrease moderately with higher wavelength.
  • the apparatus includes a first light source configured to emit infrared light into a surface of the tissue, the infrared light having a first intensity peak at a first wavelength and a second intensity peak at a second wavelength; and a detector configured to detect the transmitted light at the first and second wavelengths after passing through the tissue.
  • the first intensity peak includes light below an isosbestic point, and wherein an extinction coefficient of Hb for the light of the first intensity peak is at a proximity of a local externum point on the curve of extinction coefficient versus wavelength.
  • the second peak intensity can be above said isosbestic point and at least a portion thereof is such that an extinction coefficient of Hb for the portion is in proximity of a local maximum point on the curve of extinction coefficient versus wavelength.
  • the first wavelength can be within the range of wavelength of 756-760 nanometer, or alternatively the first wavelength is within the range of 730-734 nanometer.
  • the apparatus can further include a processor configured to calculate oxygen saturation in small arteries in the tissue by measuring a relative difference in light transmission between systole and diastole, for each of the first and second wavelengths and by calculating ratio of ratios for the first and second wavelengths wherein the ratio is a relative difference in light transmission, and the ratio of ratios is obtained by an analytical function based on modified Beer-Lambert Law.
  • the function can be any function.
  • ⁇ , SDI, ⁇ 2 and SD2 are the extinction coefficients for Hb0 2 and Hb, for the first and second wavelengths, respectively.
  • the processor can be configured to calculate oxygen saturation in small arteries in the tissue by measuring a natural logarithm of a ratio between light intensity at diastole and at systole.
  • the processor can be further configured to determine a correction factor by measuring intensity of light emitted by the light source for each of the first and second wavelength, comparing the intensity with detected intensity of light transmitted through the tissue for each of the first and second wavelength.
  • the method includes illuminating infrared light into a surface of the tissue, the infrared light having a first intensity peak at a first wavelength and a second intensity peak at a second wavelength; and detecting with a detector the transmitted light at the first and the second wavelengths after passing through the tissue.
  • the first intensity peak includes light below an isosbestic point, and wherein an extinction coefficient of Hb for the light of the first intensity peak is at a proximity of a local extremum point on the curve of extinction coefficient versus wavelength.
  • the second peak intensity wavelength can be above the isosbestic point and at least a portion thereof is such that an extinction coefficient of Hb for the portion is in proximity of a local maximum point on the curve of extinction coefficient versus wavelength.
  • the first wavelength can be within the range of wavelength of 756-760 nanometer. Alternatively, the first wavelength can be within the range of 730-734 nanometer.
  • the method can further include calculating oxygen saturation in small arteries in the tissue by measuring a relative difference in light transmission between systole and diastole, for each of the first and second peak intensity wavelengths and by calculating ratio of ratios for the first and second peak intensity wavelengths wherein the ratio is a relative difference in light transmission, and the ratio of ratios is obtained by an analytical function based on modified Beer-Lambert Law.
  • the function can be (6a)
  • ⁇ , SDI, ⁇ 2 and SD2 are the extinction coefficients for Hb0 2 and Hb, for the first and second wavelengths, respectively.
  • the step of calculating oxygen saturation in small arteries can include measuring a natural logarithm of a ratio between light intensity at diastole and at systole.
  • the step of calculating oxygen saturation in small arteries processor can include determining a correction factor by measuring intensity of light emitted by the light source for each of the first and second wavelength, comparing the intensity with detected intensity of light transmitted through the tissue for each of the first and second wavelength.
  • the step of illumination can include targeting the infrared light towards a tissue of the lungs.
  • the method can further include calculating mixed venous oxygen saturation in the tissue of the lungs.
  • the method can further include calculation of cardiac output by Fick Equation. BRIEF DESCRIPTION OF THE DRAWINGS
  • Fig. 1 is a prior art graph illustration of the extinction coefficients of the oxi- and deoxi-hemoglobin as a function of the wavelength, in the red and near-infrared regions;
  • Fig. 2 is a prior art graph of the PPG signal in the microcirculation
  • Fig. 3 is a schematic illustration of trajectories of photons transmitted via a finger tissue for a transmission mode of a pulse oximeter
  • Fig. 4 is a schematic illustration of trajectories of photons transmitted via a finger tissue for a reflection mode of a pulse oximeter
  • Fig. 5 is a graph illustration showing an absorption curves for hemoglobin and melanin and the scatter curves for the tissue and blood.
  • Figure 1 presents the extinction coefficients values for oxygenated and de- oxygenated hemoglobin, ⁇ and SD, respectively, for wavelengths between 600 nm and 900 nm.
  • the isosbestic point is for wavelength of about 800 nm.
  • the difference in extinction coefficient between Hb and Hb0 2 is relatively high, motivating the use of wavelength in the red region as the lower wavelength in conventional pulse oximetry.
  • the Hb0 2 extinction coefficient increases monotonically with the wavelength, while the Hb extinction coefficient decreases up to about 730 nm, then increases and decreases again, creating a peak at about 760 nm.
  • the light with intensity peak at a minimum or maximum of the extinction coefficient curve is less sensitive to change of extinction coefficient value due to light wavelength change.
  • the wavelength change can occur because of change of temperature or spectral change of the light passing through the tissue, due to selective absorption of photons of different wavelength, as discussed above.
  • a wavelength change of 1 nm at the minimum or at the maximum causes a relatively minor change in the corresponding extinction coefficient, with respect to a similar wavelength change of 1 nm at regions of monotonic increase or decrease of the spectral extinction coefficient curve.
  • Table 1 presents the extinction coefficients values for de-oxygenated hemoglobin, 8 D , for several wavelengths, in the neighborhood of the minimum and maximum of the extinction coefficients vs. wavelength curve, i.e. in proximity of 732 nm and 758 nm, respectively.
  • the data of the extinction coefficients values were obtained from Kim and Liu, 2007 (Ref. 11).
  • the table also presents the change in extinction coefficient when the wavelength deviated by 10 nm from the minimum or the maximum, showing that the resultant change in extinction coefficient is smaller when deviating from the minimum ,732 nm, than when deviating from the maximum , 758 nm.
  • Selecting the lower peak intensity in the two-infrared wavelengths pulse oximetry in the neighborhood of 732 nm has therefore an advantage with respect to the aspect of the deviation of extinction coefficient due to changes in the wavelength spectrum. It should be noted, however, that the selection of peak intensity having a wavelength in the neighborhood of 758 nm has two advantages in other aspects: the higher extinction coefficient for Hb results in greater difference in extinction coefficient between Hb and Hb0 2 and the difference in wavelength between the pulse oximetry lower and higher wavelengths is smaller for 758 nm, rendering smaller difference in path-length between the two wavelengths, below and above the isosbestic point.
  • the wavelength spectrum change and the resultant effective extinction coefficient change still exists. Its mean effect on the oxygen saturation can be corrected by comparing several non-invasive two- infrared Sp0 2 measurements to invasive Sa0 2 measurements, as done in commercial pulse oximeters.
  • estimation of the effective path-length in the tissue in each examination can be performed by utilizing the measurement of the intensity of the transmitted light (Is in Figure 2), compared with the intensity of the emitted light (the relative transmitted light intensity ). For each spectrum of LED and for each configuration of the pulse oximeter (reflection PPG or transmission PPG), a correction factor can be calculated in each examination, via the value of the relative transmitted light intensity in the two wavelengths.
  • an apparatus for oxygen saturation measurements in small arteries in a tissue includes a light source configured to emit light at a first and a second wavelengths into a surface of the tissue.
  • the apparatus further includes a detector configured to detect the transmitted light at the first and second wavelengths after passing through the tissue.
  • the first wavelength includes light at a wavelength for which an extinction coefficient of Hb is at a local extrema point, e.g. 732 nm.
  • the first wavelength can be below the isosbestic point, while the second wavelength is above the isosbestic point.
  • the first and second wavelengths can be selected such that the difference between an extinction coefficient of Hb and an extinction coefficient of Hb0 2 is different for each of the wavelengths. Increasing the difference increases thereby the signal.
  • the apparatus can include a processor configured to calculate oxygen saturation in small arteries in the tissue by measuring a relative difference in light transmission between systole and diastole, for each of the wavelengths.
  • the processor can be configured to calculate ratio of ratios for each of the wavelengths. More specifically the ratio of ratios can be obtained by an analytical function based on modified Beer- Lambert Law, such as: where ⁇ , SDI, ⁇ 2 and SD2 are the extinction coefficients for Hb0 2 and Hb, for the two wavelengths, respectively.
  • the processor can be configured to calculate oxygen saturation in small arteries in the tissue by measuring a natural logarithm of a ratio between light intensity at diastole and at systole, i.e.:
  • ⁇ is the extinction coefficient for the arterial blood volume increase
  • AC is the maximal increase of the hemoglobin concentration in the tissue during systole.
  • the processor can be further configured to correct errors originated from changes in wavelength spectrum of the wavelengths during transmission thereof through the tissue.
  • the processor can be configured to calculate a correction factor for each examination.
  • the correction factor can be determined by measuring the intensity of the transmitted light (Is in Figure 2), compared with the intensity of the emitted light for each of the wavelength, such that the effective path-lengths of the patient is taken into account.
  • the measurement of the oxygen saturation in the arterial systemic circulation is important in order to assess the patient's respiratory system function: lower Sa0 2 indicates respiratory dysfunction. It should be noted, that the measurement of the oxygen saturation in the arterial pulmonary circulation - the mixed venous oxygen saturation - is also of great clinical significance: it is related to the tissue metabolism and oxygen extraction and also enables the derivation of cardiac output through Fick Equation. By illuminating the thoracic wall by two wavelengths in the infrared and measuring the transmitted light in the two wavelengths through the lungs, the mixed venous oxygen saturation can be derived by Equations 6a or 6b. The technique is described in an article of Nitzan and Nitzan 2011.
  • the selection of wavelengths is also important in the measurement of the oxygen saturation in the arterial pulmonary circulation.
  • selection of the smaller wavelength of the two (below the isosbestic point) in the extrema of the Hb extinction coefficient curve is advantageous because it mitigates the effect selective absorption of the light with different wavelengths and reduces the change in the effective extinction coefficient during the passing of the light through the tissue.
  • the transmitted light through the lungs is small relative to the finger due to the greater thickness of tissue.
  • the choice of wavelength of 732 nm is preferable over that of 758 nm, because the absorption constant of the former is significantly lower.

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Abstract

L'invention concerne un appareil pour des mesures de la saturation en oxygène dans les petites artères d'un tissu. L'appareil comprend une première source de lumière conçue pour émettre une lumière infrarouge en direction de la surface du tissu, la lumière infrarouge présentant une première longueur d'onde de pic d'intensité et une seconde longueur d'onde de pic d'intensité; et un détecteur conçu pour détecter la lumière transmise aux première et seconde longueurs d'onde de pic d'intensité après avoir traversé le tissu. La première longueur d'onde de pic d'intensité comprend de la lumière en dessous d'un point isosbestique, tandis que le coefficient d'extinction de l'Hb pour la première lumière de longueur d'onde de pic d'intensité est proche d'un point externe local sur la courbe représentant le coefficient d'extinction en fonction de la longueur d'onde.
PCT/IL2018/050827 2017-07-31 2018-07-25 Procédé de mesure de la saturation en oxygène du sang artériel et appareil à cet effet Ceased WO2019026062A1 (fr)

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Cited By (4)

* Cited by examiner, † Cited by third party
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WO2020095312A1 (fr) * 2018-11-11 2020-05-14 Jerusalem College Of Technology Procédé de mesure de la concentration d'hémoglobine oxygénée et désoxygénée
CN113498326A (zh) * 2019-02-20 2021-10-12 皇家飞利浦有限公司 用于确定生理信息的设备、系统和方法
CN115721282A (zh) * 2021-08-31 2023-03-03 原相科技股份有限公司 减轻动作干扰的心律检测装置
CN115988985A (zh) * 2020-06-26 2023-04-18 艾图传感有限公司 用于补偿外周动脉张力的评估的装置和方法

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