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Restrictive lung disease is characterized by a reduced FEV1, normal FEV1/FVC ratio, and reduced total lung capacity and Dtco.

This patient has a reduced forced expiratory volume in 1 second (FEV1) but a normal FEY/forced vital capacity (FCV) ratio. This finding is compatible with restrictive lung disease rather than obstructive lung disease. The low total lung capacity is further evidence of a restrictive impairment. Restriction can be secondary to diffuse parenchymal lung disease, such as pulmonary fibrosis; in such patients, diffusing capacity of carbon monoxide (DLco) is also reduced, as it is in this patient. DLco measures the ability of the lungs to transfer gas across the alveolar-capillary membrane.

There are several causes ofreduced diffusing capacity of carbon monoxide (DLCD), including loss of surface for gas exchange (emphysema), diffuse parenchymal lung disease, and parenchymal infiltration (diffuse pneumonia). The crackles noted on pulmonary examination and the diffuse reticular infiltrate shown on chest radiograph pinpoint the lung as the cause of the restrictive abnormality. The chronic and slow progression of the symptoms and absence of fever argue against pneumonia.

Chest restriction may also result from respiratory muscle weakness as a result of neuromuscular disease and obesity. However, in these cases, the results of pulmonary examination, chest radiograph, and DLco are normal.

Although heart failure can be associated with pulmonary crackles, it is not associated with a restrictive spirometry pattern, decreased total lung capacity, or low DLco.