<prompt> A 29 year old unmarried female presents with progressive dyspnea. Her X ray chest shows clear lung fields. Pulmonary function testing reveals in FVC of 92; FEVIFVC of 89; and dICO of 59. On exercise testing her oxygen saturation drops from 92 to 86. What is the likely diagnosis:Alveolar hypoventilationPrimary pulmonary hypeensionInterstitial lung diseaseAnxiety  <response>: Answer is B Primary Pulmonary Hypeension: Isolated reduction in diffusion capacity DLCO with nearly normal flow volumes FVC; FEV1FVC 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 Robbins 7th745 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 FEVIFVC0.7 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 PPHIPAH 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 FEV1FVC 0.7 70 Severity of obstruction is based on FEV1 and FEVFVC ratio FEV1FVC 70; FEV1 80 Mild obstruction Patients in question has FEVIFVC 70 and FEV1FVC 70; FEV1 30 Moderate obstruction hence does not have an obstructive lung disease. FEV1FVC 70; FEV1 5_ 30 Severe obstruction 