Exchange gas

When a person is exposed to a volatile organic solvent through inhalation, the solvent vapor diffuses very rapidly through the alveolar membranes, the connective tissues and the capillary endothelium and into the red blood cells or plasma. With respiratory gases the whole process takes less than 0.3 seconds. This results in almost instantaneous equilibration between the concentration in alveolar air and in blood and, therefore, the ratio of the solvent concentration in pulmonary blood to that in alveolar air should be approximately equal to the partition coefficient. As the exposine continues, the solvent concentration in the arterial blood exceeds that in the mixed venous blood. The partial pressures in alveolar air, arterial blood, venous blood and body tissues reach equilibrium at steady state. When the exposure stops, any unmetabolized solvent vapors are removed from the systemic circulation through pulmonary clearance. During that period the concentration in the arterial blood is lower than in the mixed venous blood and the solvent concentration in alveolar air will depend on the pulmonary ventilation, the blood flow, the solubihty in blood and the concentration in the 

To summarize, the uptake of solvent vapors through inhalation will depend on the following factors  

Pulmonary ventilation, i.e., the rate at which fresh air (and solvent vapor) enters the lungs. This is determined by the metabohc rate and therefore depends on physical exertion. The concentration in alveolar air approaches that in inhaled air when the physical exertion is great. When exertion is low, the alveolar air concentration approaches the concentration in mixed venous blood. 

The solubility of the vapor in the blood. The higher the blood/gas partition coefficient, the more rapidly the vapor will diffuse into the blood, imtil equilibrium is achieved. At equilibrium the net diffusion between blood and air ceases, but the concentrations in air and blood may still be different. A highly soluble vapor will therefore dononstrate a lower alveolar air concentration relative to the inhaled air concentration during exposure, and a higher alveolar concentration relative to the inhaled air concentration after exposme. 

The circulation of the blood through the Ixmgs and tissues. This depends on the cardiac output and therefore, on physical exertion. For a soluble vapor, high exertion moves blood faster, increasing uptake. 

From a pathophysiologic standpoint, it is usefiil to consider respiratoiy conditions that may result in LTMV, as those characterized by failure of the lungs as a gas-exchange unit and those characterized by a failure of the ventilatory pump (Fig. 2). In some ventilated patients, psychological factors may also contribute to their degree of impairment (34). 

PMV and LTMV (18,36,37). For instance, the mean alveolar-arterial oxygen gradient in the 1419 patients enrolled in the Ventilation Outcomes Study Group was 127 mmHg (37). 

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For optimal functionaUty, platelets require a stable and weU-balanced pH, gas exchange, ambient temperature, and gentle agitation. Special plastics have been developed for optimal storage of platelets. 

Typical heat-recuperation devices are finned gas exchangers, ceramic heat wheels, and Ljungstrom air preheaters. 

These design fundamentals result in the requirement that space velocity, effective space—time, fraction of bubble gas exchanged with the emulsion gas, bubble residence time, bed expansion relative to settled bed height, and length-to-diameter ratio be held constant. Effective space—time, the product of bubble residence time and fraction of bubble gas exchanged, accounts for the reduction in gas residence time because of the rapid ascent of bubbles, and thereby for the lower conversions compared with a fixed bed with equal gas flow rates and catalyst weights. 

An unstabilized high surface area alumina siaters severely upon exposure to temperatures over 900°C. Sintering is a process by which the small internal pores ia the particles coalesce and lose large fractions of the total surface area. This process is to be avoided because it occludes some of the precious metal catalyst sites. The network of small pores and passages for gas transfer collapses and restricts free gas exchange iato and out of the activated catalyst layer resulting ia thermal deactivation of the catalyst. 

The fundamental control on the chemical contribution of the ocean to climate is the rate of gas exchange across the air-sea interface. The flux, F, of a gas across this interface, into the ocean, is often written as... 

Loss of radon in the ocean occurs typically through radioactive decay (producing four short-lived daughters before decaying to °Pb) or loss to the atmosphere at the air-sea interface. Loss of radon owing to turbulence or diffusion at the air-sea interface leads to a depletion of radon with respect to "Ra, allowing for studies on gas exchange at this interface. ... 

What functions do the stomates serve in gas exchange with the atmosphere ... 

RESPIRABLE DUST That fraction of total inhalable dust which penetrates to the gas exchange region of the lung (usually considered to be in the range 0.5 /xm-7 /xm). 

FIGURES. 17 Gas exchange beev/een alveolar and capillary compartmencs. 

Extrapulmonary airways All airways not involved in gas exchange. These... 

Parenchyma The essential or specialized part of an organ gas exchange... 

Alveoli The small terminal air sacs in the lungs, through which gas exchange between the blood and the inhaled air takes place. 

Figure 7-5 shows a typical hot carbonate system for gas sweetening. The sour gas enters the bottom of the absorber and flows counter-current to the potassium carbonate. The sweet gas then exits the top of the absorber. The absorber is typically operated at 230°F therefore, a sour/ sweet gas exchanger may be included to recover sensible heat and decrease the system heat requirements. 

Several common arrangements have been developed to improve the efficiency and/or to accomplish specific purposes, such as furnishing hot flue gas to boilers or to process gas exchangers in addition to the simultaneous generation of power or driving equipment. Figures 14-37A-D illustrate several common arrangements or cycles. 

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