Influence of age and disease severity on high resolution CT lung densitometry in asthma

Abstract

Background-Low attenuation areas (LAA) on computed tomographic (CT) scans have been shown to represent emphysematous changes in patients with chronic obstructive pulmonary disease (COPD). However, the significance of LAA is still controversial in patients with asthma. This study was undertaken to assess the usefulness of lung CT densitometry in the detection of airspace enlargement in association with asthma severity. Methods-Forty five asthmatic subjects and 15 non-smoking controls were studied to determine the influence of age, pulmonary function, and asthma severity on mean lung density ( Conclusions-Decreased CT lung density in non-smoking asthmatics is related to airflow limitation, hyperinflation and aging, but not with lung transfer factor. (Thorax 2001;56:851-856) Keywords: high resolution computed tomography; asthma severity; lung function; age Asthma is a disease characterised by airflow limitation that reverses spontaneously or in response to treatment.1 The nature of asthma as a chronic inflammatory disease of the airways is well recognised.2 This inflammation process leads to irreversible changes in the airway.3-5 Frequent airway and lung parenchymal changes associated with asthma are considered to be responsible for the irreversibility of airway obstruction, an outcome that is observed in many severe asthmatics. Emphysema, on the other hand, is defined pathologically as a process that results in the increase of distal airspaces with destruction of their walls without obvious fibrosis. 6 The evidence for the presence of emphysema in asthmatic patients is controversial.Numerous studies have demonstrated the usefulness of computed tomographic (CT) scanning and high resolution CT (HRCT) scanning to detect and quantify pulmonary emphysema in patients with chronic obstructive pulmonary disease (COPD), [7][8][9][10][11][12][13][14][15][16][17][18][19] and a quantitative method using digital data as well as visual assessment of the scan are used to analyse the CT images. Low attenuation areas (LAA) on CT scans in vivo have been shown to represent macroscopic and/or microscopic emphysematous changes in the lungs of patients with COPD.7-12 However, one report has suggested that mean lung density (MLD) gives a good indication of hyperinflation rather than of emphysema. 20Some studies have investigated the use of CT lung densitometry in non-smoking asthmatic patients. [21][22][23][24] One study suggested that the percentage of pixels below -900 Hounsfield Units (HU) at full expiration reflects air trapping in asthmatic patients and correlates with pulmonary function. 21 Gevenois et al showed that acute expiratory airflow limitation and chronic hyperinflation did not influence the MLD or the relative area of the lungs showing attenuation values less than -950 HU (RA 950 ) in nonsmoking asthmatic patients. 22 They also found that CT lung densitometry was influenced by the total lung capacity (TLC) and age in healthy subjects. Biernacki et al observed that some patients with chronic stable asthma devel...

Markers Of Vascular Perturbation Correlate With Airway Structural Change In Asthma

“…P-selectin did not correlate with airway wall area measurements (not shown). P-selectin did not correlate with measurements of lung volumes (not shown) or lung function (see Table E2); even though area of low density on MDCT less than 2950 HU at TLC correlated with FEV 1 /FVC (see Table E2) as found previously (12,14). The MDCT less than 2850 HU at FRC was also associated with FEV 1 /FVC (see Table E2) as found before (3), and with other obstructive measures (see Table E2), but did not correlate with any vascular endothelial marker (Table 5).…”

“…In emphysema, density decreases in the lung parenchyma at TLC are used to estimate change caused by hyperinflation and loss of normal lung architecture, using an empirical threshold of the percentage of lung tissue less than 2950 HU (10,11). In nonsmokers with asthma, a mosaic of similarly attenuated areas on MDCT at TLC has also been observed and has been proposed to be associated with hyperinflation, airflow limitation, and altered terminal airspace geometry (6,(12)(13)(14)(15)(16)(17). In addition, hyperinflation has been implicated as a major determinant of altered physiology in subjects with asthma (60).…”

“…In nonsmokers with severe or unstable asthma, however, low-attenuation areas at TLC have also been observed in a diffuse pattern ( Figure 1C). This pattern has been attributed in various publications to hyperinflation, airflow limitation, and complexity of terminal airspace geometry (6,(12)(13)(14)(15)(16)(17) and remains comparatively understudied in asthma relative to the more common air trapping measure at FRC.…”

Decreased computed tomographic lung density during exacerbation of asthma

“…It was demonstrated previously that some nonsmoking asthmatic patients show decreased attenuation of HRCT lung density that is related to airflow limitation, hyperinflation and ageing, but not to lung diffusing capacity [19,20]. It was also found that MLD and RA950 correlated significantly with the severity of chronic asthma.…”

“…Recently, it was shown that both MLD and RA950 are related to airflow limitation and lung volume, but not to lung diffusing capacity, and that these values correlate with the patient9s age and severity of asthma in nonsmoking asthmatics [19,20]. The present study examined differences in CT lung density between unstable asthmatics and control subjects or stable asthmatics, and whether changes occurred during exacerbation after treatment with systemic followed by inhaled glucocorticoids.…”