| NRS | neurobehavioral rating scale; normal rabbit serum; normal reference serum; numerical rating scale |
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| NRSCC | National Reference System in Clinical Chemistry |
| ORS | olfactory reference syndrome; oral rehydration solution; oral surgery, oral surgeon; Orthopaedic Res... |
| OSI | open systems interconnection [reference model] |
| PDR | pediatric radiology; peripheral diabetic retinopathy; Physicians' Desk Reference; postdelivery room;... |
| triaxial reference system | The figure resulting from rearranging the lines of derivation of the three standard limb leads of the electrocardiogram (as represented in Einthoven's triangle) so that, instead of forming the sides of an equilateral triangle, they bisect one another. Synonym: Dieuaide diagram. (05 Mar 2000) |
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