Effects of Inhaled Acid Aerosols on Respiratory Function: The Role of Endogenous Ammonia

ABSTRACT

To determine if respiratory ammonia (NH₃) alters airway responses to sulfuric acid (H₂SO₄) aerosols, 15 asthmatics inhaled a H₂SO₄ aerosol at high and low respiratory NH₃ levels. A D30 generator produced droplets with an MMAD=0.8 μm at a concentration of 350 μg/m³. All asthmatics inhaled the H₂SO₄ via a mouthpiece for 20 minutes at rest followed by 10 minutes of exercise on a bicycle ergometer. Low oral NH₃ levels averaged 63 μg/m³ while high ammonia levels averaged 340 μg/m³. Following exercise, sulfuric acid at low ammonia levels compared to high ammonia levels produced significantly greater reductions in FEV₁ (19% vs 8%, p<0.001) and maximum expiratory flow rates at 60% total lung capacity (47% vs 23%, p<0.001). These data support the hypothesis that endogenous respiratory ammonia can neutralize inhaled acid aerosols and mitigate their airway toxicity in asthmatics. Failure to eliminate oral ammonia may result in an underestimation of the effect of acid aerosols on airway function.