| ETR | effective thyroxine ratio; endothelin receptor |
|---|---|
| FEF50/FIF50 | ratio of expiratory flow to inspiratory flow at 50% of forced vital capacity |
| FEV1% | ratio of FEV1 to FVC |
| FH/BC | frontal horn/bicaudate [ratio] |
| FR | failure rate; film-screen radiograph; fasciculus retroflexus; febrile reaction; feedback regulation;... |