Respiratory tract diffusion

Acute benzene poisoning results in CNS depression and is characterized by an initial euphoria followed by staggered gait, stupor, coma, and convulsions. Exposure to approximately 4000 ppm benzene results in complete loss of consciousness. Insomnia, agitation, headache, nausea, and drowsiness may persist for weeks after exposure (126). Continued inhalation of benzene to the point of euphoria has caused irreversible encephalopathy with tremulousness, emotional lability, and diffuse cerebral atrophy (125). In deaths arising from acute exposure, respiratory tract infection, hypo- and hyperplasia of sternal bone marrow, congested kidneys, and cerebral edema have been found at autopsy. 

Airstream neutralization of acid aerosols by NH3 present in the airway-lumen reduces the health risk associated with acid particles by reducing the acid concentration prior to particle deposition.- In addition, the liquid lining of the respiratory tract probably acts as a chemical buffer," further reducing the health hazard posed by inspired acid particles. Principal factors controlling airstream neutralization of acid aerosols, which is considered to be a diffusion-limited process, are particle surface area, and particle... 

It is essentially a 2-stage process, as shown in Figure 3-5. First, there is a dissociation (dissolution) of particles then the dissolved molecules or ions diffuse across capillary walls and are taken up by the blood. Immediately following dissolution, rapid absorption is observed. For some elements, rapid absorption does not occur because of binding to respiratory-tract components. In the absence of specific data for specific compounds, the model uses the following default absorption rate values for those specific compounds that are classified as Types F (fast), M (medium), S (slow), and V (instantaneous) ... 

The Bureau of Mines, Denver Research Center and the Department of Energy, Environmental Measurement Laboratory, developed through parallel efforts, two closely related techniques for the measurement of 218p0 (RaA) diffusion coefficient spectra. This work was prompted by reports in the past 5 years indicating that the diffusion coefficient of unattached 218Po may vary due to various physical and chemical factors in different environments. The diffusion coefficient is important because it affects the amount and site of 218Po deposition in the respiratory tract. 

The acid-base chemistry of nicotine is now well known and investigations have shown that nicotine in tobacco smoke or in smokeless tobacco prodncts can exist in pH-dependent protonated or nnprotonated free-base forms. In tobacco smoke, only the free-base form can volatilize readily from the smoke particnlate matter to the gas phase, with rapid deposition in the respiratory tract. Using volatility-based analytical measurements, the fraction of nicotine present as the free-base form can be quantitatively determined. For smokeless tobacco products, the situation differs because the tobacco is placed directly in the oral cavity. Hence, the pH of smokeless tobacco prodncts can be measured directly to yield information on the fraction of nicotine available in the nnprotonated free-base form. It is important to characterize the fraction of total nicotine in its conjugate acid-base states as this dramatically affects nicotine bioavailability, because the protonated form is hydrophilic while the nnprotonated free-base form is lipophilic and thus readily diffuses across membranes (Armitage and Turner 1970 Schievelbein et al. 1973). As drug delivery rate and addiction potential are linked (Henningfield and Keenan 1993), increases in delivery rate due to increased free-base levels affect the addiction potential. 

Because the respiratory tract is an initial target of any air pollutant challenge, it usually receives primary attention in tests to determine irritant effects of exposure. Other aspects of interest include hematology, blood enzyme biochemistry, eye irritation, and p chomotor performance. Constriction of the large airways, maldistribution of ventilation due to narrowing in some small airways, constriction of peripheral lung units, and mechanical or gas diffusion impairment due to edema are possible effects of insult by pollutants. A variety of pulmonary tests is required to examine the possibilities. 

Workers exposed to an airborne fluoride concentration of 5mg/m complained of eye and respiratory tract irritation and nausea. The lethal oral dose of sodium fluoride for humans has been estimated to be 32-65 mg F/kg of body weight. Effects from ingestion are diffuse abdominal pain, diarrhea, and vomiting excessive salivation, thirst, and perspiration painful spasms of the limbs and sometimes albuminuria." Gastrointestinal effects produced after the acute ingestion of toxic amounts of fluoride likely arise from the corrosive action of hydrofluoric acid, which is produced within the acidic environment of the stomach. Cardiac arrest after accidental exposure to high levels of fluoride has been attributed to the development of hypocalcemia and/or hyperkalemia. ... 

Because of its pharmacokinetic features (pronounced bioaccessability upon oral use, diffusion to tissues and permeation into them, broad spectrum of antibacterial activity, and so on), fluoroquinolones have considerable potential for treating infections of practically any anatomic localization. Fluoroquinolones are very effective in treating infections of the respiratory tract, urinary tract, bones, skin, soft tissues, and so on. 

Any volatile material, irrespective of its route of administration, has the potential for pulmonary excretion. Certainly, gases and other volatile substances that enter the body primarily through the respiratory tract can be expected to be excreted by this route. No specialized transport systems are involved in the loss of substances in expired air simple diffusion across cell membranes is predominant. The rate of loss of gases is not constant it depends on the rate of respiration and pulmonary blood flow. 

It is important to know the diffusivities of decay products, whether as ions, neutral atoms or molecules, or as cluster ions, in order to calculate deposition in the respiratory tract. One way of doing this is to measure deposition on the walls of a tube in laminar flow. 

Unattached decay products have diffusivity appropriate to dp about 1 nm, and are almost completely retained in the respiratory tract... 

Van Zyl et al. reported on the diffusion of ipratropium through porcine bronchial epithelium tissue [74], In principle, ipratropium is administered via the respiratory tract by inhalation to treat pulmonary diseases associated with bronchoconstriction. Therefore, pulmonary absorption by bronchial tissue determines its local efficacy and was thus investigated in a diffusion cell in vitro. Bronchial epithelium was equilibrated in PBS and discs of 4 mm2 were mounted on that diffusion cell separating the donor and receiver compartment. The donor compartment contained the drug dissolved in PBS (1 mg/ml) and the receiving chamber was permanently flushed with a low flow (1.5 ml/h) of PBS thus allowing time-resolved fractionation for subsequent direct analysis by LC-ESI MS/MS in MRM mode. Transition to the product ion at m z 124 was monitored for quantification (Table 9). The transfer of ipratropium was characterized by the flux (about 220 ng/cm2/min) and the permeability coefficient calculated to be 1.6 x 10-8 cm/s. 

Most of the Al absorbed from the respiratory tract accumulates in the lungs. Pulmonary lesions have been described in employees of Al processing or manufacturing industries and encephalopathy after Al inhalation has been reported. Al is widely distributed and has many industrial uses, and toxicity from occupational exposure is assumed to be extremely rare [2, 177]. Nevertheless, a recent study investigating adverse effects on the central nervous system of Al welders found an Al-exposure-related increase in blood and urine Al concentrations, deficits in neuropsychological test performance and mild diffuse EEG abnormalities. Therefore, the potential for Al-induced neurotoxicity in those occupationally exposed to Al fumes may be greater than previously suspected [177]. 

S. pneumoniae is a common cause of acute bacterial conjunctivitis in children (Figure 25-5). Concurrent upper respiratory tract infections and otitis media, especially in children younger than 4 years, are common. In moderate climates S. pneumoniae is often the cause of acute bacterial conjunctivitis epidemics. This condition commonly presents with diffusely scattered petechial hemorrhages, especially on the superior bulbar conjunctiva, a mucopurulent discharge in the lower fornix, and transient marginal corneal infiltrates. Pseudomembranes may form. 

Aerosol particles used for inhalation deposit within the lower respiratory tract mainly by inertial impaction, sedimentation, and diffusion. Loose fractal aerosols were found to settle slower and therefore had more time to increase gravitational coagulation with other floes leading to much more rapid particle growth. This will increase the chance of the aerosol floes settling on the airway walls before reaching the end of the airways. 

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