| LSB | least significant bit; left sternal border; left scapular border; long spike burst |
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| NLS | Names Learning Test; Neu-Laxova syndrome; nonlinear least squares; normal lymphocyte supernatant |
| PLSD | protected least significant difference |
| RLS | recursive least square; restless leg syndrome; Ringer lactate solution; Roussy-Levy syndrome |
| RLSL | recursive least square lattice |
| upper motor neuron lesion | Injury to cerebral descending (corticonuclear) fibres above the brainstem or spinal motor nerve nucleus. Synonym: upper motor neuron lesion. (05 Mar 2000) |
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| upper nodal extrasystole | An obsolete term for a nodal extrasystole supposed to arise from the upper part of the A-V node; recognised in the electrocardiogram by a retrograde P wave preceding the QRS complex by an abnormally short P-R interval. (05 Mar 2000) |
| upper respiratory infection | Any number of viral or bacterial infections that includes infections of the throat, nasopharynx, sinuses, larynx, trachea or bronchi. (27 Sep 1997) |
| upper respiratory tract | The nasopharynx, oral cavity, and throat. (09 Oct 1997) |
| upper subscapular nerve | Two branches of the posterior cord of the brachial plexus, an upper and lower, supplying the subscapularis muscle; the lower subscapular nerve also supplies the teres major muscle. Synonym: nervi subscapulares. (05 Mar 2000) |
| upper thoracic splanchnic nerves | Part of the cardiopulmonary splanchnic nerves from the second to fifth segments of the thoracic sympathetic trunk that pass medially and anteriorly to enter the cardiac plexus; they convey postsynaptic sympathetic fibres to, and visceral afferent (pain) fibres from, the heart. Synonym: nervi cardiaci thoracici, upper thoracic splanchnic nerves. (05 Mar 2000) |
| upper uterine segment | The main portion of the body of the gravid uterus, the contraction of which furnishes the chief force of expulsion in labour. (05 Mar 2000) |