BME 310 Lab 5 Pulse oximeter, John G. Webster 2/20/00
Introduction
The Criticare pulse oximeter measures arterial percent oxygen saturation (SaO2 ) and pulse rate using the principles of spectrophotometry and photoplethysmography. The anesthesiologist depends on the pulse oximeter to provide early warning of malfunction of ventilator, intubation, ventilation, cardiac output, etc.
Light from two light-emitting diodes at two different wavelengths [typically 660 nm (red) and 940 nm (infrared)] passes through the tissue and is sensed by a photodiode. As the heart ejects oxygenated blood into the tissue, the instrument ignores all absorption in the steady-state tissue and measures only the absorption in the tissue that is expanded by the pressure pulse. This expanded volume contains arterial oxygenated blood.
There are two transmitter/sensor geometries. In the transmission mode, the light source and sensor are on opposite sides of the tissue being measured (such as a finger or ear lobe); the light passes through the tissue. In the reflective mode, the sensor and light source are on the same body surface (such as the chest), and the light reflects from the tissue. The finger sensor provided operates as a transmission sensor, where the multisite sensor can be used either way.
This model of pulse oximeter has an "ultrasync" feature that use the electrocardiogram (ECG) to cancel drift and motion artifact in the SaO2 signal.
Before the lab: Read material about oxygen saturation from J. G. Webster (ed.), Bioinstrumentation, Section 3.2 at the coursepage http://www.engr.wisc.edu/cgi/courses/list/bme/310/webster/
Laboratory equipment
1. Criticare Systems, 504-US Pulse Oximeter/Ultra Sync
2. CSI 504/504/US operator’s manual
3. Finger Sensor
4. Disposable ECG snap electrodes
5. Flashlight
Procedure
1. Plug CSI Model 902 DC adapter into the power line and plug the output cable into AC CHARGER input on back of 504-US. Note front panel AC green light on. Press POWER.
2. Read operator’s manual pp. 1-6 through 1-7. Line up red dots and plug in finger sensor. Note display. Apply sensor to finger. Note display.
3. Familiarize yourself with all functions and make notes in the pulse oximeter data sheet provided, consulting the operator’s manual when needed.
4. Remove sensor from finger to obtain alarm, then replace.
5. Unplug sensor to obtain alarm, then replace.
6. Press PULSE VOLUME. Press again.
7. Press and hold PULSE VOLUME to obtain each possible number on screen.
8. Remove sensor to cause alarm, then press ALARM SILENCE key. Record time for alarm to resume.
9. Set alarm to each possible volume.
10. Press and hold ALARM SILENCE to obtain each possible number on screen.
11. Press ALARM MENU.
12. Press TREND and note change after each press.
13. Press EVENT, wait about 1 min, and note mark on screen.
14. Press MAGNIFY.
15. Scroll forward using arrow buttons.
16. Attach three (RA, LA, LL) disposable electrode as shown on operator’s manual, page 3-4. Connect leads to oximeter. Obtain display of ECG and pulse. On alarm menu, set print to 00:00. Press WAVEFORM until both ECG and pulse waveform are displayed. Press PRINT (on top). Record the time delay from the R wave to the pulse upstroke. Calculate estimated pulse wave velocity = (measured distance from heart to finger)/delay.
17. Demonstrate the effect of bright ambient light on operation using fluorescent light (which contains little red and infrared light) and tungsten light from flashlight (which contains much red and infrared light).
18. Demonstrate ultra-sync mode operation. Ultra-sync can be turned on and off by holding ALARM MENU button until second menu is reached and then toggling the ultra-sync option. Compare motion artifact with and without ultra-sync mode operation.
19. Monitor ECG on one subject, while monitoring O2 sat on a different subject. Demonstrate ultra-sync operation. Explain changes in pulse waveform as compared to a single subject setup. Look for and sketch distortions in wave shape.
20. Observe O2 saturation before, during, and after exercise. Explain any changes.
21. Exhale as far as possible. Then hold breath as long as possible. Explain any changes.
22. Breathe into plastic bag containing volume roughly equal to your chest as long as you can. Explain any changes. If available, repeat with 50% air, 50% N2 mixture.
23. Observe the effect on the pulse waveform of squeezing the finger sensor. Explain.
Results
1. The SaO2 measurement is based on absorbance. Explain how the 2-wavelength method allows accurate SaO2 measurements in people with vastly different skin pigmentation.
2. Sketch the SaO2 probe. Is it a transmission or reflective device? Explain the advantages/disadvantages of each type. Explain forehead operation versus finger operation.
3. Explain how photoplethysmography is used to obtain the pulse waveform.
4. Give the results of pulse wave velocity in procedure 16.
5. In procedure 17, explain the effect of each light source.
6. In procedure 18, explain the effect of sync mode.
7. In procedure 20, explain the result.
8. In procedure 21, explain the result.
9. In procedure 22, explain the result.
10. In procedure 23, explain the result.
11. Suggest a way to make the device more user friendly to nontechnical health care personnel.
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BME 310 Lab 5 Pulse oximeter, John G. Webster 2/20/00
Pulse oximeter data sheet. Your name:
Name / Function / Levels or limits / Control sequencePulse volume
Alarm silence
Magnify
Event
Trend
Waveform
Alarm menu
Feed
O2 sat high alarm
Pulse low alarm
Smart alarms
Show alarms
Averaging times
Ultrasync
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