Flow-volume loops following acute bronchodilator treatment

The dashed flow volume curve in each panel is the predicted relationship. A: The TLC is unchanged after bronchodilator therapy, but there is a fall in residual volume (RV) and an increase in total flow but not in peak expiratory flow (PEF). B: The bronchodilator causes an increase in flow rates without a shift in lung volume. In these first two examples, the measurement of lung volume is essentially noncontributory, as the FEV1 alone would be sensitive to the changes. C: The pre-bronchodilator flow-volume curve is shifted right and down, indicating hyperinflation and airflow limitation. The post-bronchodilator loop is markedly improved, although airflow is not totally normal. D: The change caused by bronchodilation is solely a fall in lung volumes, but flow at any given absolute volume (eg, dashed vertical line indicates an isovolume point for comparison) is significantly improved. The FEV1 may not change in this situation which is an example of an "isovolume shift."