Respiratory physiology alveolar

Voisin C, Aerts C, Pommery-Dutriez N, et al. 1981. Effects of gaseous pollutants on alveolar macrophages An in-vitro cytotoxicity test using cellular cultures in gas phase. In Meeting European Society for Clinical Respiratory Physiology, Gothenburg, Sweden, June 2-5, 1981. Eur J Respir Dis Suppl 62 187-188. 

Various conventional medical applications for infrared gas analyzers have been described in the literature continuous analysis of COj in respired air (Domhorst et a/., 1953) alveolar CO2 measurement (Collier et al., 1955) measurement of CO2 in respired gas mixtures (Cullen et al., 1956) measurement of CO2 in respired gases containing cyclopropane and ether (Linde and Lurie, 1959) and application to anesthesia and respiratory physiology (Powell, 1965). 

These results show that retinyl esters in respiratory epithelium and in alveolar cells form a pool of vitamin A, which can be used physiologically by the tissue. The formation of retinol and at least RA from retinyl esters is strictly controlled. So far an unphysiological formation of RA and a subsequent toxicity seems not possible. Retinyl esters, however, are biochemically inert with respect to gene expression or vitamin A activity as long as they are not hydrolyzed. Consequently, the inhalative application, especially in cases of insufficient lung development, could represent a true alternative. The oral contribution is hardly successful because of the poor RBP s)mthesis of the liver and the lack of availability of a parenteral solution is currently not available. 

The partial pressure of CO is important in connection with a number of physiological problems. For example, respiratory acidosis is the result of an abnormally high p... CO . The value of arterial pC O varies directly with changes in the metabolic production of CO and indirectly with the amounl of alveolar ventilation. The problem is more commonly ihe result of decreased alveolar ventilation caused by abnormally low CO excretion by the lungs (alveolar /ivpoveniilulion). 

Figure 27.6. Ultrastructure of the alveolar respiratory membrane shown in cross section. (Adapted from Guyton, A. C., and Hall, J. E. Textbook of Medical Physiology, 10th edition, W.B. Saunders, Philadelphia, 2000. This figure was completely redrawn by the author from materials cited.)...

Particles much greater than 5 to 10 pm in diameter are usually removed by the upper respiratory system, and those smaller than 5 pm can penetrate deep into the alveolar spaces of the lung. Thus 5 to 10 pm is often considered to be the upper diameter for aerosols of physiological interest. 

Markers of physiological effects can be useful in identifying early changes in respiratory functions of the lung due to inhaled material. Biomarkers are available to measure lung mechanical properties, ventilation, expiratory flow, intrapulmonary gas distribution, alveolar-capillary gas exchange, and perfusion. Such measurements have been used to test the effects of exposure to an array of inhaled toxicants. These assays can reveal functional manifestation of structural changes in the respiratory system, whether... 

Careful patient selection prevents unsafe levels of alveolar hypoventilation with subsequent hypoxemia and hypercapnea, especially if the tidal volume leakage is >20%. Any compensatory increase in respiratory rate and shortened expiratory time, attributable to the air leakage, may aggravate dynamic hyperinflation, especially among patients with airflow obstruction (15). Ventilator-supported speech has been reported in patients with neuromuscular diseases (NMD) and intact bulbar function (16-19). The physiologic characteristics that enable this population to tolerate ventilator-supported speech include little or no decrease in chest wall or lung compliance and the absence of airflow obstmction. Therefore, patients with NMD may be ventilated with a deflated or cuffless tracheostomy tube accepting the modest compromise in alveolar ventilation (16,20-22). Patient populations, such as those with chronic obstructive pulmonary disease may be able to tolerate cuff deflation for short periods provided there is adequate supervision. 

The clearance of particles from the respiratory tract may be viewed as the first line of defense of the respiratory tract to protect the body from toxic effects of the deposited particles. The responses of the respiratory tract will also vary depending on where the particles are deposited, extending from the nares to the alveolar spaces (see Fig. 8). Although the clearance of particles and related activities are initiated as physiologically adaptive responses, they can progress and become pathological responses, as will be discussed later. 

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