• BME 210

BME 210 Lab Report - Oxygen Measurement

John Webster (lab partners Tom Edison and Carrie Nation) 1/9/18

Abstract

We constructed a PO$$_2$$ sensor from parts and used it to measure PO$$_2$$. PO$$_2$$ of inhaled air was 152 mm Hg whereas that of exhaled air was 114 mm Hg. The sensor time constant was 20 s. The PO$$_2$$ of tap water was 76 mm Hg, but increased to 85 mm Hg when stirred.

Introduction and purpose

Our metabolism requires oxygen. We need to know the partial pressure of oxygen in the arterial and venous blood to assess how well the lungs and heart are oxygenating the tissues. We will construct a PO$$_2$$ sensor from parts, measure its time constant, and use it to measure PO$$_2$$ in liquids and gases. We will measure how much the PO$$_2$$ changes between inhaled and exhaled air.

Experimental procedure

Following instructions in the notes, we assembled the Clark electrode and connected it to the variable voltage circuit shown in the notes. We used DMMs to obtain current vs. polarizing voltage. We calibrated the differential O$$_2$$ analyzer.

Results

Note results on the data sheet. Numbered answers to numbered questions follow:

1. Current vs. polarizing voltage is plotted.
2. PO$$_2$$ of our exhaled air was 114 mm Hg.
3. We excluded the first portion of the breath because the dead space has room air which does not participate in gas exchange.
4. Difference in O$$_2$$ concentration was 38 mm Hg.
5. 38 mm Hg compared well with respiratory flow experiment.
6. Decreasing time constant of response is 20 s, measured at 63% of the step change. Increasing time constant is 18 s, which compares well.
7. Time constant is determined by slow gas diffusion through plastic membrane.
8. Deionized water had PO$$_2$$ of 8 mm Hg.
9. PO$$_2$$ of fountain water was 76 mm Hg.
10. Electrode in stirred water increased to 85 mm Hg.
11. Increase was due to eliminating stagnant water near electrode and bringing fresh water near membrane.

Conclusions

Electrodes can measure PO$$_2$$ in water or air. The time constant is about 20 s. Electrodes should be moved to prevent stirring artifact.

Last updated:
January 7, 2018