Ventilation heterogeneity is increased in adults exposed to coal mine fire-related PM2.5.

BACKGROUND AND OBJECTIVES: The Hazelwood Health Study was set up to study long-term health effects of a mine fire that blanketed residents of the Latrobe Valley with smoke for 45 days in 2014. The Respiratory Stream specifically assessed the impact of fine particulate matter <2.5 µm diameter (PM2.5) exposure from mine fire smoke on lung health. The multiple breath nitrogen washout (MBW) test assesses ventilation heterogeneity, which may detect sub-clinical airways dysfunction not identified using standard tests such as spirometry. This analysis assessed the association of PM2.5 exposure with measures of ventilation heterogeneity. METHODS: Exposed (Morwell) and unexposed (Sale) participants were recruited 3.5-4 years after the fire from those who had participated in an Adult Survey. MBW was performed to measure lung clearance index (LCI), functional residual capacity (FRC), acinar (Sacin) and conductive (Scond) ventilation heterogeneity. PM2.5 exposure was estimated with emission and chemical transport models. Multivariable linear regression models were fitted controlling for confounders. RESULTS: We recruited 519 participants. MBW tests were conducted on 504 participants with 479 acceptable test results (40% male; 313 exposed, 166 unexposed). Exposure to mine fire-related PM2.5 was associated with increasing Scond (ß = 1.57/kL, 95%CI: 0.20-2.95, p = 0.025), which was comparable to the estimated effect on Scond of 4.7 years of aging. No other MBW outcomes were statistically different. CONCLUSION: Increasing exposure to PM2.5 was associated with increased ventilation heterogeneity in the conductive region of the lungs 4 years after the event.

Small airways dysfunction is associated with increased exacerbations in patients with asthma.

There is a poor understanding of why some patients with asthma experience recurrent exacerbations despite high levels of treatment. We compared measurements of peripheral ventilation heterogeneity and respiratory system mechanics in participants with asthma who were differentiated according to exacerbation history, to ascertain whether peripheral airway dysfunction was related to exacerbations. Three asthmatic groups: "stable" (no exacerbations for >12 mo, n = 18), "exacerbation-prone" (≥1 exacerbation requiring systemic corticosteroids within the last 12 mo, but stable for ≥1-mo, n = 9), and "treated-exacerbation" (exacerbation requiring systemic corticosteroids within the last 1 mo, n = 12) were studied. All participants were current nonsmokers with <10 pack yr smoking history. Spirometry, static lung volumes, ventilation heterogeneity from multibreath nitrogen washout (MBNW), and respiratory system mechanics from oscillometry were measured. The exacerbation-prone group compared with the stable group had slightly worse spirometry [forced expired volume in 1 s or FEV1 z-score -3.58(1.13) vs. -2.32(1.06), P = 0.03]; however, acinar ventilation heterogeneity [Sacin z-score 7.43(8.59) vs. 3.63(3.88), P = 0.006] and respiratory system reactance [Xrs cmH2O·s·L-1 -2.74(3.82) vs. -1.32(1.94), P = 0.01] were much worse in this group. The treated-exacerbation group had worse spirometry but similar small airway function, compared with the stable group. Patients with asthma who exacerbate have worse small airway function as evidenced by increases in Sacin measured by MBNW and ΔXrs from oscillometry, both markers of small airway dysfunction, compared with those that do not.NEW & NOTEWORTHY This study assessed the relationship between peripheral airway function, measured by multiple breath nitrogen washout and oscillometry impedance, and exacerbation history. We found that those with a history of exacerbation in the last year had worse peripheral airway function, whereas those recently treated for an asthma exacerbation had peripheral airway function that was comparable to the stable group. These findings implicate active peripheral airway dysfunction in the pathophysiology of an asthma exacerbation.