E.V. Stepanov, Yu.A. Shulagin, E.V. Babarskov, A.I. Diachenko, A.V. Koval, E.A. Tischenko

Modern techniques of high sensitive gas analysis including methods based on laser spectral analysis give a possibility for high sensitive and accurate measurements of endogenous CO content in exhaled air and to study its dynamics at various breath maneuvers and loading test. One of the possible diagnostic applications of this analytical approach is related with the direct definition of diffusion properties of alveolar-capillary lung membrane based on data on dynamic of endogenous CO accumulation in lung air at breath holding. This technique could appear as more simple and easy alternative to the conventional approach based on single-breath test and widely used for lung disease diagnostics in pulmonology. In the presented paper peculiarities of exogenous carbon monoxide (CO) diffusion from alveolar air to blood through the alveolar-capillary lung membrane at conventional single breath test and diffusion of endogenous CO from blood to alveolar air at breath holding were considered in frame of the same calculation model. A three compartment model of gas exchange between blood and alveolar air was used in this study. It includes air in lung alveolar volume containing O2 as well as endogenous or exogenous CO, lung capillary blood plasma containing dissolved O2 and CO, and blood cells, containing oxyhemoglobin and carboxyhemoglobin. Due to the difference of condition of CO bounding by blood cells in these two cases the dynamic of CO content variation in lung caused by these differently directed diffusion processes was demonstrated could be described by two different time constants. In the case of the conventional single-breath test it-s value is defined by the process of the CO molecule diffusion through the alveolar-capillary membrane as well as the rate of CO bounding by blood cells. In the case of endogenous CO diffusion from blood it is defined by only the diffusion properties of lung membrane. A new approach for experimental definition of the lung diffusion capacity was proposed on the basis of the obtained result. This method could be based on measurement of rate of endogenous CO accumulation in alveolar air at breath holding with help of high sensitive techniques of laser-based gas analysis. Simultaneous application of both considered techniques gives an opportunity to define the diffusion properties of lung membrane itself together with the lung capillary blood volume and the rate of CO bounding by red cells and to use these data for differential diagnostics of lung diseases of respiration and blood systems, for example chronic obstructive pulmonary disease and pulmonary arterial hipertension