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 Oxygen transport in blood Hemoglobin Oxygen O Deoxygen +O O Oximeters

3 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, 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 3

4 Oxyhemoglobin dissociation curve Oximeters 4

5 Beer-Lambert s law Oximeters 5

6 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 6

7 Molar absorptivities of hemoglobin and oxyhemoglobin Oximeters 7

8 Electromagnetic spectrum Oximeters 8

9 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 O O C Oximeters 9

10 Light absorption signal produce AC output produce DC output Oximeters 10

11 SaO 0 d d C C IR IR O O IR e I I 0 d d C C R R O O R e I I IR O O IR R O O R DC IR IR DC R R C C C C I I I I IR R ln ln O R R O IR IR R IR O O IR R IR R C C C SaO Oximeters 11

12 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 1

13 NIRS sensing by LEDs An sensor with central emitter and eight surrounding, detachable detectors Oximeters 13

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

15 Cerebral functional areas Oximeters 15

16 Neurovascular coupling Neurovascular coupling produces changes in blood flow and oxygen consumption Oximeters 16

17 Continuous-wave NIRS Ratio of reflected to incident light intensity, I/I 0, depends Absorption coefficient Changes of hemoglobin concentration [O ] [H] Path length L and differential path length factor B A I ln I O 0 u L [ O ] H [ H] B L Oximeters 17

18 Continuous-wave NIRS cont. Using two NIRS lights with different wavelengths for computing the change of hemoglobin concentrations ] [ ] [ O H O H H H O H O H O O u u H u u O Oximeters 18

19 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 19

20 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

21 Related functional area for NIRS Prefrontal cortices PFC Premotor cortices PMC Supplement motor areas SMA Sensorimotor cortices SMC Oximeters 1

22 Brain oxygenation & reorganization in stroke patients Before rehabilitation oxy After rehabilitation Gait task Total oxy deoxy Lesion Lesion

23 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 3

24 Vessel occulsion test

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

26 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.