Oximeters. Hsiao-Lung Chan, Ph.D. Dept Electrical Engineering Chang Gung University, Taiwan

Transcription

1 Oximeters Hsiao-Lung Chan, Ph.D. Dept Electrical Engineering Chang Gung University, Taiwan

2 Pulse oximeter Masimo pulse CO-oximeter ts/continuous/radical-7/ Oximeter

3 Oxygen transport in blood Hemoglobin Oxygen Hb HbO Deoxygen Hb Hb Hb+O HbO Oximeters 3

4 Arterial saturation of oxygen SaO SaO is affected by partial pressure of arterial oxygen, PO. At low partial pressures, such as tissue capillary pressure of 40 mmhg Millimeter of mercury Oxygen is released from hemoglobin, leading to a low SaO of about 75%. At high partial pressures, such as pulmonary capillary pressure of 95 mmhg Oxygen binds with hemoglobin, leading to high SaO of about 95 mmhg. Oximeters 4

5 Oxyhemoglobin dissociation curve Oximeters 5

6 Shifts of the oxyhemoglobin dissociation curve CO reacts with water to form carbonic acid HCO 3, which dissociates into hydrogen ions H + and bicarbonate ions HCO 3 When blood temperature increases, oxygen delivery to tissues is increased, making more oxygen available for binding to hemoglobin. BPG,3 biphosphoglycerate is a metabolically important phosphate compound. BPG concentration increases during hypoxic conditions of longer than a few hours. Oximeter 6

7 Carbon monoxide-hemoglobin dissociation curve A CO partial pressure of only 0.4 mmhg in alveoli causes CO to compete equally with oxygen for hemoglobin binding 1/50 of normal alveolar oxygen pressure of 100 mmhg. A CO partial pressure of only 0.6 mmhg can be lethal. Oximeter 7

8 Beer-Lambert s law Oximeters 8

9 Light interaction with absorption effect Beer-Lambert s law I x x I x di x ai x dx ax I x I x e 0 ai x x Absorbance of a wavelength of light absorption path length, l concentration, c absorbing species by ελ, molar absorptivity Oximeters 9

10 Oxygen saturation SaO, SpO measurement Relative amount of oxygen carried by the hemoglobin Two specific wavelengths : λ 1 : a red wavelength eg. 660 nm λ : a near infrared wavelength eg. 805 nm SaO C C HbO HbO C Hb Oximeters 10

11 Electromagnetic spectrum Oximeters 11

12 Light absorption signal produce AC output produce DC output Oximeters 1

13 SaO 0 10 d d C C IR Hb Hb IR HbO HbO IR I I 0 10 d d C C R Hb Hb R HbO HbO R I I Hb Hb IR HbO HbO IR Hb Hb R HbO HbO R DC IR IR DC R R C C C C I I I I IR R log log HbO R Hb R HbO IR Hb IR Hb R Hb IR Hb HbO HbO IR R IR R C C C SaO 13

14 Molar absorptivities of hemoglobin deoxyhemoglobin and oxyhemoglobin Oximeters 14

15 Total absorbance in tissue Scattering Variable absorbance not due to arterial blood Nonspecific sources of optical attenuation such as light scattering and geometric factors Oximeter 15

16 Pulse oximeter Takuo Aoyagi recognized that only pulsatile changes in light transmission through living tissues were necessary for estimating hemoglobin concentrations. Aoyagi s pulsatile observation is summarized in ratio calculations Zeros because each absorbance are constant The pulsatile path lengths for Hb and HbO are assumed to be equal Biopotential amplifiers 16

17 Arterial saturation of oxygen SaO Oximeter 17

18 Approximation of R in actual implementation AC refers to the pulsatile component of transmitted light DC refers to the nonpulsatile component of transmitted light Biopotential amplifiers 18

19 Calibration curve Scott Wilber made pulse oximetry accurate by abandoning the Beer-Lambert law R-vs.-SaO calibration curve was converted to a software lookup table for later real-time SpO estimation. Oximeter 19

20 Photodetector circuits /36086/does-this-photodiode-circuit-work

21 Wearable photoplethysmographic biosensors H.H. Asada et al, IEEE EMB, 003 Oximeter 1

22 Adaptive noise canceler Oximeter

23 Rapid desaturation-resaturation occurring during tapping motion Control A healthy volunteer inspired air from a face mask, in which the fraction of inspired oxygen was adjusted to decrease the control SpO values down from 100% to approximately 70% and up to 100% again. Masimo SET uses adaptive noise cancellation to minimize the motion effect Nellcor N 00, Nellcor N 3000 pulse oximeters Oximeter 3

24 Masimo s signal extraction technology SET adaptive noise cancellation Oximeter 4

25 Masimo s SET cont. Masimo s original signal extraction technology SET algorithm for adaptive noise cancellation. Ratios R corresponding to SpO values are input to the reference signal generator to output candidate noise sources. Each candidate noise source is input to the adaptive filter, with the filter output power then plotted A peak power corresponding to a lower SpO value may correspond to the ratio associated with saturation of venous blood rv. Oximeter 5

26 Masimo s SET cont. Because of two wavelengths, there are two input signals The reference noise source is defined as a function of the ratio Oximeter 6

27 Near-infrared spectroscopy NIRS by laser diode Uses the near-infrared region from 800 nm to 500 nm Applications in pharmaceutical and medical diagnostics including blood sugar and oximetry. OxiplexTS, ISS Inc, USA Oximeters 7

28 NIRS sensing by LEDs An sensor with central emitter and eight surrounding, detachable detectors Oximeters 8

29 Evoked cerebral function examination Electroencephalography EEG Near infrared NIR Magnetoencephalography MEG Functional MRI

30 Cerebral functional areas Oximeters 30

31 Neurovascular coupling Neurovascular coupling produces changes in blood flow and oxygen consumption Oximeters 31

32 Continuous-wave NIRS Ratio of reflected to incident light intensity, I/I 0, depends Absorption coefficient Changes of hemoglobin concentration [O Hb] [HHb] Path length L and differential path length factor B A I ln I OHb 0 u L [ O Hb] HHb [ HHb] B L Oximeters 3

33 Continuous-wave NIRS cont. Using two NIRS lights with different wavelengths for computing the change of hemoglobin concentrations ] [ ] [ Hb O HHb Hb O HHb HHb HHb Hb O HHb Hb O HHb Hb O Hb O u u HHb u u O Hb Oximeters 33

34 Application in brain oxygenation With 0% of oxygen consumption occurring in the human brain, any deficiency in oxygen supply may result in injury OxiplexTS, ISS Inc, USA Biomedical Optic 34

35 Cerebral Near-Infrared spectroscopy monitoring Monitoring of cerebral oxygenation Carotid stenosis or occlusion Brain ischemia Sleep apnea Ischemia of rat model Ischemia Cerebral response to carotid balloon inflation Obstructive sleep apnea

36 Related functional area for NIRS Prefrontal cortices PFC Premotor cortices PMC Supplement motor areas SMA Sensorimotor cortices SMC Oximeters 36

37 Brain oxygenation & reorganization in stroke patients Before rehabilitation oxyhb After rehabilitation Gait task TotalHb oxyhb deoxyhb Lesion Lesion

38 Application in peripheral vascular disease PVD PVD is a narrowing of the vessels carrying blood to the muscles in the legs and arms. Most patients report experiences of pain in the extremities due to inadequate blood flow and oxygen delivery to the exercising muscle. OxiplexTS, ISS Inc, USA Oximeters 38

39 Vessel occulsion test

40 NIRS demonstration Pulse Oximetry NEJM Muscular oxygenation under exercise Functional NIRS

41 Reference G. D. Baura, Medical device technologies, Elsevier Inc., 01. JG. Webster, Medical Instrumentation, application and design, 3rd, Houghton Mifflin, 000. JJ.Carr, JM.Brown, Introduction to Biomedical Equipment Technology, 4nd Edition, Prentice-Hall, 000.