Defaecation syncope: new light on an old problem

Syncope, the sudden loss of consciousness with spontaneous recovery, is a frequent clinical problem for which patients are commonly referred for evaluation [1]. While a number of conditions may result in syncope, one particular group of causes has been the subject of intense study over the last two decades. For years prior to this it had been postulated that many episodes of unexplained syncope occurred due to periods of decompensation in the autonomic nervous system that would lead to hypotension (with or without bradycardia) sufficiently profound so as to cause cerebral hypoperfusion and loss of consciousness, an entity known as vasovagal (or more recently as neurocardiogenic or reflex) syncope. In a landmark paper by Kenny and colleagues, head upright tilt table testing was introduced as a method for provoking autonomic nervous system decompensation in a laboratory setting [2]. This not only provided a long sought after diagnostic modality for unmasking vasovagal syncope, but also introduced a controlled setting in which detailed measurements and observations could be made during the syncope itself. Consequently, there has been a sudden and tremendous increase in our knowledge concerning these disorders. At the same time, it has become evident that classic vasovagal (neurocardiogenic) syncope is but one aspect of a broad, heterogenous collection of disturbances in the body's autonomic nervous system, which lead to alterations in normal homeostatic mechanisms to a sufficient extent so that loss of … Fax: +1-419-383-3041. E-mail address: bgrubb{at}mco.edu.