]> 2026-07-31T07:51:21+00:00 WBR1109 0 en 30 mmHg; Chlamydia psittaci infection Chlamydia psittaci is a cause of pneumonia in individuals exposed to pigeon droppings. Chlamydia psittaci would not cause an acute exacerbation on exposure to pigeon droppings. 15 mmHg; Chlamydia psittaci infection Chlamydia psittaci is a cause of pneumonia in individuals exposed to pigeon droppings. Chlamydia psittaci would not cause an acute exacerbation on exposure to pigeon droppings. 30 mmHg ; Hypersensitivity pneumonitis Recall that the equation for A-a gradient is PAO2-PaO2. PaO2 can be measured in the patient’s blood. PAO2 is given by the following equation: 150-PaCO2/0.8 = 150-40/0.8=100; 100-70=mmHg. The patient in this vignette has developed a subtype of hypersensitivity called Bird Fancier’s Lung. 20 mmHg ; Hypersensitivity pneumonitis The calculation of A-a gradient in this answer is incorrect. Please see the explanation for a proper calculation. 20 mmHg; Asthma exacerbation While the acute exacerbation of the patient’s condition on exposure to an environmental antigen resembles an asthma exacerbation, the specific history in this case is telling. This patient has developed a subtype of hypersensitivity pneumonitis called Bird Fancier’s disease. The patient in this vignette has contracted a subtype of hypersensitivity pneumonitis called “Bird Fancier’s Lung”. This disease is caused by the exposure to avian proteins present in the dry dust of the droppings and sometimes in the feathers of a variety of birds. People who work with birds or own many birds are at risk. Bird hobbyists and pet store workers may also be at risk. This question requires that test takers calculate the Aveolar-arterial (A-a) oxygen gradient. Recall that the equation for A-a gradient is PAO₂ - PaO₂. PaO₂ can be measured in the patient’s blood. PAO₂ is given by the following equation: '''150 - (PaCO₂/0.8) = 150 - (40/0.8) = 100''' The A-a gradient is the PAO₂ - PaO₂: '''100 - 70 = 30 mmHg'''<br/> '''Educational Objective:''' The Aveolar-arterial (A-a) gradient is defined as the difference between PAO2 and PaO2. “Bird Fancier’s Lung” is a type IV hypersensitivity reaction.<br/> '''References:''' First Aid 2014 page 605 (Hypersensitivity pneumonitis)<br> Funke M, Fellrath JM. Hypersensitivity pneumonitis secondary to lovebirds: a new cause of bird fancier's disease. Eur Respir J. 2008;32(2):517-21. Immunology Pathophysiology William J Gibson (Reviewed by Serge Korjian) C Pulmonology 2020-10-28T02:38:41Z 2459150.6101968 WBR1109