Alveolar

Human evolution has taken place close to sea level, and humans are physiologically adjusted to the absolute partial pressure of the oxygen at that point, namely 21.2 kPa (159.2 mm Hg), ie, 20.946% of 101.325 kPa (760 mm Hg). However, humans may become acclimatized to life and work at altitudes as high as 2500—4000 m. At the 3000-m level, the atmospheric pressure drops to 70 kPa (523 mm Hg) and the oxygen partial pressure to 14.61 kPa (110 mm Hg), only slightly above the 13.73 kPa (102.9 mm Hg) for the normal oxygen pressure in alveolar air. To compensate, the individual is forced to breathe much more rapidly to increase the ratio of new air to old in the lung mixture. 

The onset of action is fast (within 60 seconds) for the intravenous anesthetic agents and somewhat slower for inhalation and local anesthetics. The induction time for inhalation agents is a function of the equiUbrium estabUshed between the alveolar concentration relative to the inspired concentration of the gas. Onset of anesthesia can be enhanced by increasing the inspired concentration to approximately twice the desired alveolar concentration, then reducing the concentration once induction is achieved (3). The onset of local anesthetic action is influenced by the site, route, dosage (volume and concentration), and pH at the injection site. 

Ethylene is slightly more potent as an anesthetic than nitrous oxide, and the smell of ethylene causes choking. Diffusion through the alveolar membrane is sufficiendy rapid for equilibrium to be estabUshed between the alveolar and the pulmonary capillary blood with a single exposure. Ethylene is held both ia cells and ia plasma ia simple physical solution. The Hpoid stroma of the red blood cells absorb ethylene, but it does not combine with hemoglobin. The concentration ia the blood is 1.4 mg/mL when ethylene is used by itself for anesthesia. However, ia the 1990s it is not used as an anesthetic agent. 

In an animal study of rats exposed by inhalation to ethylene oxide at 10, 33, or 100 ppm for approximately two years (245), and in a separate chronic rat study in which rats were exposed to 50 or 100 ppm of ethylene oxide (240), increased incidences of mononuclear cell leukemia, peritoneal mesothelioma, and various brain tumors have been reported. In an NTP (246) two-year inhalation study of mice at 50 and 100 ppm, alveolar/bronchiolar carcinomas and adenomas, papillary cystadenomas of the harderian gland, and malignant lymphomas, uterine adenocarcinomas, and mammary gland tumors were increased in one or both exposure groups. 

Fig. 7-2. Particle deposition as a function of particle diameter in various regions of the lung. The nasopharyngeal region consists of the nose and throat the tracheobronchial region consists of the windpipe and large airways and the pulmonary region consists of the small bronchi and the alveolar sacs. Source Task Group on Lung Dynamics, Health Phys. 12, 173 (1966).

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

TABLE 5.6 Effect of Dead Space Volume, Tidal Volume, and Breathing Frequency on Alveolar >fentllation at a Fixed Minute Ventilation (V = 58.0 Umin). Modified from Chemiack. ... 

Alveolar ventilation supplies O2 to the bloodstream while alveolar capillary perfusion provides alveolar gas with COj. Resting individuals consume approximately 250 mL 02/min and produce approximately 200 ml. COi/min because, stoichiometrically, metabolic processes require a greater supply of O, than the quantity of CO2 produced. Defining the respiratory exchange ratio, R, as... 

Alveolar duct Airway distal to respiratory bronchiole leading to individual alveoli and alveolar sacs. 

Alveolar gas transport Exchange of oxygen and carbon dioxide between al-... 

Alveolar sac Group of alveoli originating from an expansion of the alveolar... 

Alveolar ventilation Volume of air passing through the alveoli and alveolar... 

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