Alveolar steady state

Absorption. -Hexane is absorbed by passive diffusion in the lungs. Oral and dermal absorption have not been studied, but absorption by these routes is probably by the same process. Alveolar ra-hexane reaches a steady state with the -hexane in blood as -hexane is distributed and metabolized in the body more is absorbed from the alveolar air. In studies with humans, there was no evidence of saturation up to... 

During inhalation anesthesia, the partial pressure of the inhaled anesthetic in the brain equals that in the lung when steady-state conditions are achieved. Therefore, at a given level (depth) of anesthesia, measurements of the steady-state alveolar concentrations of different anesthetics provide a comparison of their relative potencies. The volatile anesthetic concentration is the percentage of the alveolar gas mixture, or partial pressure of the anesthetic as a percentage of 760 mm Hg (atmospheric pressure at sea level). The minimum alveolar anesthetic concentration (MAC ) is defined as the... 

Washout When the administration of an inhalation anesthetic is discontinued, the body now becomes the source that drives the anesthetic into the alveolar space. The same factors that influence attainment of steady-state with an inspired anesthetic determine the time course of clearance of the drug from the body. Thus, nitrous oxide exits the body faster than halothane. 

Ethylene oxide is readily taken up by the lung. At steady state, 20-25% of inhaled ethylene oxide reaching the alveolar space is exhaled as unchanged compound and 75-80% is taken up by the body and metabolized. Aqueous ethylene oxide solutions can penetrate human skin. 

For the calculation of arterial blood concentration, CBarteriai, it is assumed that steady state in the lung is quickly reached upon inhalation, that the exhaled concentration is in equilibrium with the concentration in the arterial blood, and that the chemical is absorbed only in the alveolar region. Consequently a species balance on TCE within the arterial blood gives... 

Oghiso Y, Kubota Y, Takahashi S, et al. 1988. Effect of 89Sr-induced monocytopenia on splenic and pulmonary alveolar macrophage populations in a normal steady state. J Radiat Res 29 189-202. 

There are two techniques used to measure diffiision capacity. In one procedure, the subject takes a single vital capacity inspiration of a dilute mixture of CO and holds his breath for 10 seconds. In the second, the subject breathes a low concentration of CO (about 0.1%) for 30 seconds until a steady state has been reached. In both methods, the rate of disappearance of the CO from the alveolar gas is calculated by measuring the concentrations of CO in the inspired and expired air with an infrared analyzer. The larger the diffiising capacity (DlCO), the more CO enters the blood and the lower the amount of CO measured in the expired gas. 

In an extension of Gray s early work, Lloyd and Cunningham (38) tried to quantify the ventilatory response at steady state in terms of the alveolar 02 and C02 tensions. By having subjects breath gas mixtures high in C02 at different alveolar oxygen partial pressures, the curves shown in Figure 5 were obtained. Based upon these observations, the steady-state ventilation was described by... 

When a person is exposed to a volatile organic solvent through inhalation, the solvent vapor diffuses very rapidly torough the alveolar membranes, fire connective tissues and the capillary endothelium and into fire 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, flierefore, the ratio of the solvent concentration in pulmonary blood to that in alveolar air should be approximately equal to the partition coefficient. As the exposure 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 fire 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 solubifity in blood and the concentration in the... 

The steady-state gas concentrations within an alveolus reflect the balance of inflow to outflow, as shown in the control volumes (dashed lines) of Fig. 4.12. For CO2 in the alveolar space, net inflow by perfusion must equal the net outflow 1 ventilation, = Va(Cac - where... 

The rate of removal of CO2 from the blood initially exceeds the rate of its production by the tissues the rate of uptake of oxygen by the blood is scarcely increased because, before hyperventilation, the haemoglobin is almost saturated with O2. The blood CO2 loss therefore initially exceeds oxygen uptake. When a new steady state is attained, CO2 loss returns to normal, with alveolar PCO2 low. 

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