Source: International Congress 2016 – Non-inflammatory assessment of airway disorders
Disease area: Airway diseases

Abstract

IntroductionMeasuring small airway function is difficult. Current measures do not test gas transfer. We set out to establish if the A-a oxygen gradient differed with asthma severity.MethodsNormal controls, mild/moderate people with asthma, and people with severe asthma (by ATS criteria) were recruited. Asthma was defined as; Methacholine PC₂₀<8mg/ml, 15% FEV₁ reversibility or PEF variability >20%. Mild/moderate asthma was diagnosed if no major and only one minor criterion for severe asthma were met. Controls had normal spirometry and Mch PC₂₀.A-a gradient was measured on ear lobe capillary blood, taken on room air, and calculated using the ideal air equation, corrected for barometric pressure. 5 flow FeNO was also measured.ResultsThe A-a oxygen gradient was higher in severe asthma compared with controls (mean difference 2.15 KPa, p=0.01 [95% CI 0.95 to 3.3]) and was also higher in mild/moderate asthma compared with normal controls (mean difference 1.29 KPa, p=0.024 [95% CI 0.17 to 2.4]).There was a trend for increased A-a gradient with increasing asthma severity independent of age, spirometry and gender; p=0.012 for trend by severity, effect size 0.82KPa, (95% CI 0.19, 1.6).

Markers of small airway function and demographics

	control 9	mild/mod 23	refractory 15
% male	33	66	53
ICS dose	0	500 (649)	1840 (855)
PO steroid (g)	0	0	7.7 (6.5)
% pred FEV1	107 (0.16)	89 (0.17)	74 (0.17)
A-a grad	0.71 (0.53)	2 (1.6)	2.9 (1.5)
Alveolar NO *	4.3 (0.06)	4.6 (0.1)	6.7 (0.08)
Bronchial NO *	153.6 (0.17)	139.8 (0.06)	121.7(0.08)
DNO *	5 (0.19)	9.7 (0.05)	13.8 (0.08)

 

ConclusionSevere asthma is associated with an increasing A-a gradient. The A-a gradient may reflect distal airway inflammation in severe asthma.
Values are mean (SD) except * where values are geometric mean (log SEM)

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Citations should be made in the following way:
Dominick Shaw (Nottingham, United Kingdom), Dominick Shaw, Ireti Adejumo, Ruth Green, Ian Pavord. Alveolar-arterial oxygen gradient in asthma. Eur Respir J 2016; 48: Suppl. 60, 1026

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