CO diffusing capacity

Respiratory function tests should be conducted before exposure and, at least, after the final exposure and at the end of a recovery period. Components that may be studied include compliance, total lung capacity, functional residual capacity, forced vital capacity, resistance, and CO diffusing capacity (Harkema et al., 1982 Sun et al., 1987). 

Breathing rates and CO diffusing capacity were not affected, but residual volume was significantly... 

The CO diffusing capacity, DPco, of sheep was measured at various 02 tensions in a hyperbaric chamber using a method similar to that outlined above (12). DPco varied as a function of the oxygen tension. In Figure 2 the reciprocal of DPco is plotted as a function of the reciprocal of the diffusing capacity of the maternal and fetal red blood cells. From the plot the slope is the reciprocal of the value of V, the maternal and fetal capillary blood volume while the intercept is the reciprocal of Dmco- From these studies we calculated that the resistance of maternal and fetal red blood cells was approximately one-third of the total resistance while the resistance of the placental membrane per se was about two-thirds of the total resistance to 02 diffusion (12). This is in contrast to previous studies which assumed that the placental membrane per se constituted the total resistance to diffusion. 

The CO diffusing capacity, DLCO, is calculated by measuring the difference in alveolar CO concentrations at the beginning and end of a period of breath holding. The test begins by having die patient exhale completely to RV and then inspiring rapidly to TLC a breath of gas with a known CO concentration. After a 10-second breath-hold, the patient exhales rapidly (Fig. 21.14). The initial portion of this exhalation is discarded, as it contains gas from die dead space, and a portion of the subsequently exhaled gas, assumed to be well-mixed alveolar gas, is analyzed for CO content The initial alveolar concentration of CO is not the inspired concentration, as the inspired gas is diluted... 

Primary pulmonary diseases (e.g. primary pulmonary hypertension, pulmonary fibrosis, chronic obstructive respiratory diseases) cause chronic hepatic congestion due to chronic pulmonary heart disease, possibly leading to insufficiency. Hypoxaemia as a result of acute or chronic respiratory insufficiency can impair metabolic liver functions considerably. In 40—70% of patients with cirrhosis, hypoxaemia can be found in about 50% of cases with advanced cirrhosis, a reduced diffusion capacity for CO is detectable. Furthermore, pulmonary tissue contains a high level of glutamine synthetase, so that ammonia detoxification is possible (ultimately by perivenous hepatocytes) before the blood reaches the systemic circulation. In existing pulmonary diseases, localized ammonia detoxification is impaired. 

The diffusing capacity of the lung for carbon monoxide (CO) is a measure of the ability of the alveolar capillary membrane to transfer or conduct gases from the alveoli to the blood. This transport process is entirely a passive one brought about by diffusion. As described previously in Section 2.2, the barriers for diffusion consist of surfactant, alveolar epithelium, interstitital fluid, capillary endothelium, plasma, and the red blood cell membrane. 

The normal diffusing capacity value for an adult at rest is about 25 ml/min-ute/mm Hg for CO. This value is reduced, however, when diffusion is impaired as a result of certain pathologic states that lengthen the barrier for diffusion (e.g., interstitial edema, alveolar edema, and fibrous tissue deposition) or decrease the area for diffusion (e.g., emphysema and nonventilated alveoli). 

Inhaled NO can be used during cardiac catheterization to evaluate safely and selectively the pulmonary vasodilating capacity of patients with heart failure and infants with congenital heart disease. Inhaled NO also is used to determine the diffusion capacity (Dl) across the alveolar-capillary unit. NO is more effective than CO in this regard because of its greater affinity for hemoglobin and its higher water solubility at body temperature. 

Most of the patients with allergic alveolitis show decreased lung function with a typical restrictive pattern (Rankin et al. 1962 Bishop et al. 1963 Williams 1963 Hapke et al. 1968). Obstructive changes have been described, however (Pepys and Jenkins 1965 Warren et al. 1978 Bourke et al. 1989). In addition, there is a decrease in the diffusion capacity (the transfer factor of the lung for carbon monoxide TL,CO) due to the inflammatory infiltration in the alveolar septa (Williams 1963 Seal et al. 1968 Warren et al. 1978). Lung... 

The airflow limitation will be mirrored by a reduction in the FEVi/FVC ratio, FEVi and expiratory flow. In patients with symptomatic COPD, and especially with emphysema, the diffusion capacity (TL,CO, Kco) is reduced. Reduction in Kco is associated with the severity of the emphysema assessed by CT scanning (Gould et al. 1991). Static lung volumes, TEC and RV will be normal or increased. The severity of the airflow limitation in COPD is graded arbitrarily by the reduction in FEVp Mild FEVj a80% of predicted... 

Again, some points about this result deserve attention. First, the product KA is normally called the diffusing capacity, which is descriptive but conceals its relation to mass transfer. Second, K includes mass transfer resistances in the lung gas, across the alveoli walls, and into the blood. The resistance in the gas is probably small because diffusion in gases is fast. The resistance in the blood may be small because of the fast reaction between CO and hemoglobin which accelerates mass transfer this acceleration is discussed in detail in Chapter 17. The resistance across the membrane may be rate controlling. 

The proportionality constant K includes the rate constant of the combustion, thermal capacity of the pellistor, and the factor related to the diffusion of the gas. Ideally, all terms on the right-hand side of (3.18) except Co are constant. For safety applications, the response of the pellistor is expressed on the scale of %LEL, which for methane is % 100 T, F.T. = 5% v/v in air. On the LEL scale, the dynamic range is between 10% and 100%. The response time is around 1 s. 

Table 1 gives the components present in the crude DDSO and their properties critical pressure (Pc), critical temperature (Tc), critical volume (Vc) and acentric factor (co). These properties were obtained from hypothetical components (a tool of the commercial simulator HYSYS) that are created through the UNIFAC group contribution. The developed DISMOL simulator requires these properties (mean free path enthalpy of vaporization mass diffusivity vapor pressure liquid density heat capacity thermal conductivity viscosity and equipment, process, and system characteristics that are simulation inputs) in calculating other properties of the system, such as evaporation rate, temperature and concentration profiles, residence time, stream compositions, and flow rates (output from the simulation). Furthermore, film thickness and liquid velocity profile on the evaporator are also calculated. 

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