Intensive Care Medicine (ICM) Practice Exam

In restrictive pulmonary disease like fibrosis, what is characteristic of the flow volume loop?

1. Increased overall lung volume

2. Reduction in peak expiratory flow

3. Variability in forced expiratory time

4. Narrowed loop with increased lung volume

The correct answer is: Reduction in peak expiratory flow

In restrictive pulmonary diseases such as pulmonary fibrosis, the key characteristic observed on the flow-volume loop is a reduction in peak expiratory flow. This reduction occurs because, in restrictive conditions, lung expansion is limited, which translates into decreased total lung capacity and reduced airflow during forced expiration. As the lung volume is lower, peak expiratory flow rates are diminished compared to healthy lungs, leading to a distinctive pattern on the flow-volume loop. The flow-volume loop in restrictive disease typically displays a narrowed shape when compared to that in normal lung function due to the reduced total volume of air that can be exchanged. The maximum airflow achieved during expiration is constrained because the lungs are unable to inflate fully, which correlates with the decrease in peak expiratory flow observed in these conditions. This narrowing does not indicate increased lung volume, nor does it show variability in forced expiratory time, as both of these features are more characteristic of obstructive lung diseases rather than restrictive ones. In summary, the narrowing of the flow-volume loop and reduction in peak expiratory flow are hallmark features of restrictive lung disease, effectively illustrating the impaired lung mechanics associated with conditions like pulmonary fibrosis.