Partial pressures of oxygen and carbon dioxide

As explained in the previous section, the P02 of the atmosphere is 160 mmHg. The partial pressure of carbon dioxide (PC02) is negligible (see Table 17.1). As air is inspired, it is warmed and humidified as it flows through the conducting airways. Therefore, water vapor is added to the gas mixture. This is accounted for in the calculation of P02 in the conducting airways  

The partial pressure of the water vapor is 47 mmHg and, as a result, the P02 is slightly decreased to 150 mmHg. The PC02 remains at 0 mmHg. By the time the air reaches the alveoli, the POz has decreased to about 100 mmHg. The P02 of the alveolar gas is determined by two processes  

The PCOz of the alveoli is about 40 mmHg and is also determined by two processes  

As cellular metabolism increases, the rate of production of carbon dioxide also increases. Typically, increased activity is associated with an increase in ventilation so that the increased amounts of carbon dioxide delivered to the lungs are eliminated. Hypoventilation impairs the elimination of carbon dioxide and causes an increase in alveolar PC02. 

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List the partial pressures of oxygen and carbon dioxide in various regions of the respiratory and cardiovascular systems... 

Table 17.1 Partial Pressures of Oxygen and Carbon Dioxide...

Figure 46-10 Partial pressures of oxygen and carbon dioxide in air, blood, and tissue. Values shown are approximations in mm Hg and calculated assuming a 5% shunt. Heavy arrows show directions of gradients. (Modified from Tietz NW. Fundamentals of clinical chemistry, 3rd ed. Philadelpbla WB Saunders Co, 1987.)...

In order to achieve direct combination of carbon and oxygen at an appreciable speed it is necessary, of course, to operate at an elevated temperature. However, this does not affect the issue, because it was shown in 2 4 that the maximum useful work is independent of whether or not the system passes through intermediate temperatures different from 20 C. The real difficulty is to achieve reversibility in the reaction process itself. At any chosen operating temperature the partial pressure of oxygen and carbon dioxide above the carbon, at equilibrium, are in a constant ratio as determined by the equilibrium constant... 

EXERCISE 5.10 A 10.0-L flask contains 1.031 g O2 and 0.572 g CO2 at 18°C. What are the partial pressures of oxygen and carbon dioxide What is the total pressure What is the mole fraction of oxygen in the mixture ... 

Figure 6.7. Partial pressures of oxygen and carbon dioxide in arterial blood (y-axis) as a function of time (x-axis). At time zero, ventilation ceases, e.g. as a result of a plastic bag put over the head. Inset the oxygen dissociation curve shown for reference see text for description.

The diffusion of oxygen and carbon dioxide also depends on their partial pressure gradients. Oxygen diffuses from an area of high partial pressure in the alveoli to an area of low partial pressure in the pulmonary capillary blood. Conversely, carbon dioxide diffuses down its partial pressure gradient from the pulmonary capillary blood into the alveoli. 

This thermodynamic coupling between oxygen and carbon dioxide exhibited in water will also occur between any two gases in any solvent. A physiological example of this is the solubility of oxygen and carbon dioxide in blood, where it is found that increasing the partial pressure of Oo at fixed CO2 partial pressure results in an increased oxygen concentration in blood and decreased carbon dioxide concentration. Also, the situation is reversed if the CO2 partial pressure is increased at fixed O2 partial pressure. This phenomenon was first experimentally observed in 1914 and is referred to as the Bohr effect. 

A hybridoma can live indefinitely in a growth medium that includes salts, glucose, glutamine, certain amino acids, and bovine serum that provides essential components that have not been identified. Serum is expensive, and its cost largely determines the economic feasibihty of a particular ciilture system. Only recently have substitutes or partial replacements for serum been found. Antibiotics are often included to prevent infection of the culture. The pH, temperature and dissolved oxygen, and carbon dioxide concentration must be closely controlled. The salt determines the osmotic pressure to preserve the integrity of the fragile cell. 

Table VI summarizes the material presented in the previous discussion. It correlates the changes in oxygen and carbon dioxide partial pressures, showing the pathological causes for the imbalances. In addition, it contains the various diagnoses of acid-base abnormality (using same numbers as in Figures 1 and 2 and Table I). Considering the format of Table VI as a tic-tac-toe set-up, we can label the nine portions by the letters A-I for identification in Table VII which gives examples of various conditions associated with such blood gas abnormalities (20-30).

Snider, G. L. Interpretation of the Arterial Oxygen and Carbon Dioxide Partial Pressures A Simplified Approach for Bedside Use. Chest (1973), 6, 801 - 806. 

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