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Chapter: Medical Electronics - Bio-Chemical and Non Electrical Parameter Measurement

pO2 Measurement

The term po2 is defined as the partial pressure of oxygen respectively.

pO2 MEASUREMENT

 

The term pO2 is defined as the partial pressure of oxygen respectively. The determination of  pO2  is one the most important physiological chemical measurement. The effective functioning of both respiratory and cardiovascular system can be by pO2 measurement. The partial pressure of a gas is proportional to the quantity of that gas present in the blood.

 

The platinum wire, which is an active electrode, is embedded in glass for insulation and only its tip is exposed. It is kept in the electrolyte solution in which the oxygen is allowed to diffuse. The reference electrode is made up of silver-silver chloride (Ab/AgCl). A voltage of 0.7 is applied between the platinum wire and the reference electrode. The negative terminal is connected to the active electrode through a micro ammeter and the positive terminal is given to the reference electrode.


 

Due to the negative terminal, the oxygen reduction takes place at the platinum cathode. Finally the oxidation reduction current proportional to the partial pressure of oxygen diffused into the electrolyte can be measured in the micro ammeter. The electrolyte is generally scaled in the electrode chamber by means of a membrane through which the oxygen can diffuse from the blood or sample solution.

 

There are two types of pO2 measurement. They are

 

I)                  Vitro measurement

 

II)               Vivo measurement

 

In case of dark electrode the platinum cathode and the reference electrode is present in a single unit. This electrode is used for vitro and vivo measurements.

 

In Vitro Measurements

 

In this method the blood sample is taken and the measurement for oxygen saturation is made in the laboratory. The electrode is placed in the sample blood solution and the pO2 value is determined.

 

In Vivo Measurements

 

In this method the oxygen saturation is determined while the blood is flowing in the circulatory system. A micro version of the pO2 electrode is placed at the tip of the catheter so that it can be inserted into various parts of the heart or circulatory system.

 

The pO2 measurement also has some disadvantages in it. The reduction process in the platinum cathode removes a finite amount of the oxygen from the cathode. And there is a gradual reduction of current with respect to time. However careful design and proper procedures in modern pO2 electrodes reduce the errors.

 

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