What is Neurally Mediated Hypotension ?

Neurally mediated hypotension, or NMH, refers to a drop in blood pressure that occurs after being upright. We define NMH by a drop in systolic BP of 20 mm Hg (compared to the BP measured when the person is lying flat) during standing or upright tilt table testing. Although NMH may be slightly more common in people with a low resting blood pressure, most people who develop NMH during standing have a normal resting blood pressure. NMH is an abnormality in the regulation of blood pressure during upright posture. It occurs if too little blood circulates back to the heart when people are upright, a situation that can trigger an abnormal reflex interaction between the heart and the brain that results in a lowering of blood pressure. NMH is sometimes known by the following names: the fainting reflex, delayed orthostatic hypotension, neurocardiogenic syncope, vasodepressor syncope, vaso-vagal syncope. Syncope is the medical term for fainting.

Neurally mediated hypotension occurs when there is an abnormal reflex interaction between the heart and the brain, both of which usually are structurally normal.

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