Answer is B (Primary Pulmonary Hypeension): Isolated reduction in diffusion capacity (DLCO) with nearly normal flow volumes (FVC; FEV1/FVC) in a young female with progressive dyspnea is characteristic of Primary Pulmonary Hypeension. Features of Primary Pulmonary Hypeension / Idiopathic Pulmonary Aerial Hypeension Most common in Young women who are 20-40 years of Age (Robbin's 7th/745) (strong female predominance) Most cornmon symptom is exeional dyspnea (predominant symptom is dysnea) Pulmonary Function tests Are usually normal with the exception of DLCO which is characteristically reduced. Non obstructive PFT (FEVI/FVC>0.7 or 70%) Non restrictive PFT (FVC > 80%) DLCO2 is reduced (.DLCO) (Note: Mild restrictive effects can be seen in upto 20% of patients with advanced IPAH) X Ray chest X Ray chest shows clear lung fileds in PPH/IPAH X Ray chest usually shows enlargement of pulmonary aeries Exercise tolerance Exercise tolerance is markedly reduced (The exercise capacity of these patients appears to be limited by a low cardiac output because of a decrease in the functional pulmonary vascular bed) Understanding the PFT results of the patient in question The patient in question has an almost normal PFT with the exception of a reduced DLCO. The patient in question does not have a restrictive disease as FVC >80% Severity of restrictive disease is based on the assessment of FVC. FVC < 80% Mild restriction Patient in question with an FVC of 92% is not a FVC < 70% Moderate Testriction case of restrictive pulmonary disease FVC < 50% Severe Restriction The patient in question does not have a obstructive lung disease as FEV1/FVC > 0.7 (70%) Severity of obstruction is based on FEV1 and FEV/FVC ratio FEV1/FVC 70; FEV1 >80% Mild obstruction Patients in question has FEVI/FVC > 70% and FEV1/FVC 70; FEV1 > 30% Moderate obstruction hence does not have an obstructive lung disease. FEV1/FVC 70; FEV1 5_ 30% Severe obstruction