| FIF50 | forced inspiratory flow at 50% of forced vital capacity |
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| FIO2 | forced inspiratory oxygen; fractional concentration of oxygen in inspired gas |
| FIS | forced inspiratory spirogram; free induction signal |
| FIV | feline immunodeficiency; forced inspiratory volume |
| FIV1 | forced inspiratory volume in one second |
| late diastolic murmur | A murmur heard at the end of ventricular diastole (during atrial systole if in sinus rhythm), usually due to obstruction at one of the atrioventricular orifices. Synonym: atriosystolic murmur, late diastolic murmur. (05 Mar 2000) |
|---|---|
| Frantzel's murmur | A murmur of mitral stenosis when louder at its beginning and end than in its midportion. (05 Mar 2000) |
| friction murmur | The sound, heard on auscultation, made by the rubbing of two opposed serous surfaces roughened by an inflammatory exudate, or, if chronic, by nonadhesive fibrosis. Synonym: friction murmur, friction rub. (05 Mar 2000) |
| functional murmur | A cardiac murmur not associated with a significant heart lesion. Synonym: innocent murmur, inorganic murmur. (05 Mar 2000) |