<s>[INST] context: Primary pulmonary hypeension Once again I remind you What is FEV,% ??? FEV, is also expressed as a ratio or percentage of the FVC and can be written as %FEV1 rather than FEV,/FVC. Once again make it clear "FEV, expressed as percentage (FEV,%) is actually FEV ,/ FVC." If the individual being tested displays a low FEV, and the FEV,% is also low, then the clinician should suspect the presence of obstructive pathologies. In patients with restrictive lung diseases - FVC low - FEV, is also low, (hut there is less reduction in comparison to FVC). Since both of these values may be equally affected in restrictive lung disease the %FEV, is normal or sometimes it is increased because the decrease in FEV, is less compared to decrease in FVC. Hence when % FEV, is between 85% - 100% of the normal and if both FEV, and PVC are low then you should suspect the patient of having restrictive lung disease. Major clues given in the question are :? Decreased DLCO --> (Normal predicted range is 75-120%) Normal FEV1IFVC --> (Normal predicted range is 88% - 90%) Normal FVC (FVC > 80% is considered normal) Beside these patient is having decrease in oxygen saturation on exercise. These abnormalities suggest primary pulmonary hypeension. Interstitial lung disease can be ruled out because of nonnal ITC (FVC is reduced in restrictive lung disease). Obstructive lung disease can he ruled out because of normal FEV/FVC and normal FVC. Primary pulmonary hypeension Age group Most common in young women (20-40 years of age). Symptom Most commonly present with exeional dypnoea. Pulmonary function test Usually presents with restrictive pattern of disease FVC Normal to decrease FEV/FVC Normal to decrease DLCO --> Decrease out of propoion to FVC Patient with primary pulmonary hypeension can presents with restrictive pattern of disease but the decrease DLCO is out of propoion to the decrease in FVC. Exercise tolrence Markedly reduced Chest X-ray Clear lung field, enlargement of pulmonary aery. [/INST] question: A 29 yr old unmarried female presents with dyspnea her chest X-ray is normal, FVC is 92%, FEVI/FVC is 89% and DLCO is 59% of nonnal. On exercise her oxygen saturation drops from 92% to 86%. What is the likely diagnosis aEUR' | options: A: Alveolar hypoventilation B: Primary pulmonary hypeension C: Interstitial lung disease D: Anxiety | answer: C </s>