Blood-gas barrier

The lung contains more than 40 different types of cells, amongst which epithelial cells are vital for maintenance of the pulmonary blood-gas barrier. The epithelium also provides absorptive and secretive functions. The diversity of epithelial cell types is summarized as airway epithelium and alveolar epithelium cells. 

Fig. 1 Schematic representation of the blood-gas barrier at the level of the alveolus-pulmonary capillary...

In other applications of CT, orally administered barium sulfate or a water-soluble iodinated CM is used to opacify the GI tract. Xenon, atomic number 54, exhibits similar x-ray absorption properties to those of iodine. It rapidly diffuses across the blood brain barrier after inhalation to saturate different tissues of brain as a function of its lipid solubility. In preliminary investigations (99), xenon gas inhalation prior to brain CT has provided useful information for evaluations of local cerebral blood flow and cerebral tissue abnormalities. Xenon exhibits an anesthetic effect at high concentrations but otherwise is free of physiological effects because of its nonreactive nature. 

The thickness of the blood-gas interface is normally less than 0.5 (im. This extremely thin barrier promotes the diffusion of gases. The thickness may increase, however, under conditions of interstitial fibrosis, interstitial edema, and pneumonia. Fibrosis involves the excess production of collagen fibers by fibroblasts in the interstitial space. Edema is the movement of fluid from the capillaries into the interstitial space. Pneumonia causes inflammation and alveolar flooding. In each case, the thickness of the barrier between the air and the blood is increased and diffusion is impaired. 

The ability of the anesthetic agent to function is related to the partial pressure of the drug in the brain. Two major factors dictate the concentration of anesthetic agent in the neural tissue (1) the pressure gradients from lung alveoli to the brain (i.e., inhaled gas —> alveoli — bloodstream —> brain) and (2) the lipid solubility of the drug that enables it to pass between the blood-brain barrier to the central nervous system. 

Gao B, Hagenbuch B, Kullak-Ublick GA, Benke D, Aguzzi A, Meier PJ. Organic anion-transporting polypeptides mediate transport of opioid peptides across blood-brain barrier. J Pharmacol Exp Ther 2000 294(l) 73-79. 

Rosenberg GA, Kornfeld M, Estrada E, Kelley RO, Liotta LA, Stetler-Ste-venson WG. TIM P-2 reduces proteolytic opening of blood-brain barrier by type IV collagenase. Brain Res 1992 576 203-207. 

All inhaled anaesthetic drugs must be soluble in blood and brain in order to pass across the alveolar-capillary membrane and the blood-brain barrier. The term used to quantify solubility is partition coefficient. For anaesthetic purposes this is defined as the ratio of the concentration of dissolved gas/vapour in the blood to the concentration in the alveoli at... 

Nitrous oxide is rapidly absorbed from the alveoli. Due to its low blood/gas solubility equilibrium is rapidly established between the alveoli and the blood, and across the blood-brain barrier (Figure 3.1). The vast majority of... 

Rosenberg GA, Estrada EY, Dencoff JE (1998) Matrix metal-loproteinases and TIMPs are associated with blood-brain barrier opening after reperfusion in rat brain. Stroke 29 2189-2195... 

When oedema fluid collects in the tissues of the skin, it gives a puffy look to the skin of the face. In the lung, the capillaries run close to the alveoli, and reduction in plasma oncotic pressure can result in fluid accumulation in the alveolar wall and in the alveoli. This fluid increases the diffusion distance for oxygen between blood and alveolar air and acts as a diffusion barrier, reducing gas exchange. If severe, lung (pulmonary) oedema can result in development of abnormal blood gas concentrations. Treatment of pulmonary oedema is critical as it can develop into a life-threatening situation. 

Pfefferkom T, Rosenberg GA (2003) Closure of the blood-brain barrier by matrix metalloproteinase inhibition reduces rtPA-mediated mortality in cerebral ischemia with delayed reperfusion. Stroke 34 2025-2030... 

Rosenberg GA, Dencoff JE, Correa N Jr., Reiners M, Ford CC (1996b) Effect of steroids on CSF matrix metaUoproteinases in multiple sclerosis relation to blood-brain barrier injury. Neurology 46 1626-1632... 

Pozzilli C, Bemai di S, Mansi L, Picozzi P, lannotti F, Alfano B, Bozzao L, Lenzi GL, Salvatore M, Conforti P, Fieschi C (1988) Quantitative assessment of the blood-brain barrier permeability in multiple sclerosis using 68-Ga-EDTA and positron emission tomogi aphy. J Neurol Neurosurg Psych 51 1058—1062. 

Persidsky Y, Heilman D, Haorah J, Zelivyanskaya M, Persidsky R, Weber GA, Shimokawa H, Kaibuchi K, ficezu T (2006) Rho-mediated regulation of tight junctions during monocyte migration across blood-brain barrier in HIV-1 encephalitis (HIVE). Blood 107 4720 730. 

Diffusion Carbon monoxide diffusing capacity Measurement of efficiency of alveolar gas exchange decreases with thickening of alveolar blood-air barrier... 

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