Detection of early lung impairment with aerosol bolus dispersion

Abstract

The broadening of inhaled aerosol boluses (aerosol bolus dispersion) during respiration provides a noninvasive measure of convective gas mixing in the lungs. In this study, the sensitivity and specificity of this technique for the diagnosis of early lung impairment due to cigarette smoking was evaluated.Two hundred and sixteen randomly selected subjects (126 smokers and 90 nonsmokers) were investigated with aerosol dispersion in comparison to conventional lung function tests. The cumulative cigarette consumption of the subjects was quantified by "pack-years" (PY). Smokers were classified into the following groups: 0< PY ≤10; 10< PY ≤20; 20< PY ≤30; and PY >30.Forced expiratory volume in one second (FEV 1 ), maximal expiratory flow at 25, 50 and 75% vital capacity (MEF 25 , MEF 50 and MEF 75 ) decreased significantly with increasing cigarette consumption. In comparison to nonsmokers, FEV 1 was significantly reduced in smokers of 10< PY ≤30, and MEF 75 was significantly reduced in smokers of PY >20. Aerosol bolus dispersion increased with increasing PY. For all groups of smokers, even those with PY <10, bolus dispersion was significantly increased in comparison to lifelong nonsmokers, indicating alterations in convective gas mixing in the lungs. Calculation of receiver operating characteristics for the lung function parameters under consideration showed that bolus dispersion has a higher sensitivity and specificity than conventional lung function parameters.Hence, the aerosol bolus dispersion test could be a promising epidemiological tool to study early abnormalities in intrapulmonary gas mixing due to environmental factors. Eur Respir J., 1994Respir J., , 7, 1830Respir J., -1838 Various severe and epidemiologically important lung diseases originate in the lung periphery [1]. Chronic obstructive pulmonary disease (COPD) and asthma are diseases which are associated with a destruction, obstruction, or inflammation of peripheral airspaces. Unfortunately, conventional tests of lung function, such as spirometry or body-plethysmography, suffer from a lack of sensitivity in detecting such early peripheral lung impairment. Forced expiratory flow rates and total airway resistance reflect properties of the central airways and are almost unaffected by changes in the smaller airways [2]. On the other hand, it has been shown that the regional distribution of inhaled air is altered in smokers with normal spirometry [3]. Therefore, lung function tests which are sensitive for changes in lung ventilation pattern are supposed to be more suitable for the early detection of changes in the lung periphery caused by smoking and, presumably, other exogeneous factors.The aerosol bolus dispersion technique, applying boluses of submicron aerosol particles as a lung probe, delivers a quantitative measure of convective mixing in the lungs. This technique has been used for diagnostic purposes in several studies [4,5], and has shown interesting capabilities which promise to provide a powerful supplement to conventional lung function...

Saline aerosol bolus dispersion. I. The effect of acinar airway alteration

“…5) were actually consistent with the ranges of values encountered in the literature using nonhygroscopic aerosols. Combing data from various previous reports (4,5,7,18) using nonhygroscopic aerosols in the 0.5-1 m size range, we found that H values for healthy subjects ranged 180-300 ml for VLD ϭ 200 ml and 400-600 ml for VLD ϭ 800 ml.…”

“…On the basis of previous observations by others (1,5,22) in which smokers were essentially characterized by a steeper increase of dispersion between shallow and deep VLD levels, we also computed for each subject the increase of the dispersion indexes H and between VLD ϭ 200 ml and VLD ϭ 800 ml [e.g., ⌬H ϭ H(800 ml) Ϫ H(200 ml)]. The resulting ⌬H and ⌬ are summarized in Table 2, in which smokers showed a significantly larger dispersion increment between 200 and 800 ml for ⌬H as well as for ⌬ (for cutoffs 5 and 15%).…”

“…Previous aerosol bolus dispersion studies in smokers made use of 0.5 m triphenyl phosphate (15), 1-m latex particles (1) or 0.8-m oil droplets (5,22). We used a nebulized saline aerosol that is generally referred to as unstable.…”

“…Despite these drawbacks, the bolus dispersion test seems to pick up even subtle lung structural changes (1,5,15,22), and we therefore further explored the possibilities of the technique in the case of mild lung alteration. We have used an aerosol bolus dispersion test similar to the one previously employed by others (1,5,22) but substituted nebulized saline for latex microsphere (1) or oil droplet (5,22) aerosols.…”

“…We have used an aerosol bolus dispersion test similar to the one previously employed by others (1,5,22) but substituted nebulized saline for latex microsphere (1) or oil droplet (5,22) aerosols. The rationale for using saline was that, in the VLD range (200-800 ml) and particle range (0.5-1 m) of interest for detection of lung structural change (1,5,22), bolus dispersion appears to be only poorly sensitive to aerosol particle size (9,19,21) and bears no causal relationship to deposition (1,18,22). As a consequence, dispersion of the exhaled bolus is still expected to be similar to that obtained with monodisperse nonhygroscopic aerosols in a similar size range.…”