Orthostatic Hypotension Variants, POTS, and Less Well-Defined Autonomic Dysfunction

Abstract

Orthostatic intolerance results from maladaptation of circulatory system to the effects of gravitational force in upright position. Two main forms of orthostatic intolerance with distinct haemodynamic changes are orthostatic hypotension (OH) and postural orthostatic tachycardia syndrome (POTS). Orthostatic hypotension has three main variants defined by their temporal relationship to the act of standing: initial (10–30 s after standing), classical (1–3 min after standing) and delayed OH (beyond 3 min of standing), the two latter are characterized by persistent blood pressure (BP) fall. In POTS there is no BP fall on standing but excessive and continuous orthostatic tachycardia, usually accompanied by a spectrum of unspecific symptoms such as dizziness, discomfort, nausea, chest pain and palpitation. Symptoms of OH and POTS may be debilitating and occasionally manifest as syncope and fall injuries, the latter often observed in older individuals. The prevalence of OH increases with age, ranging from less than 5% below 40 years to more than 20% above 70 years, and with comorbidities, such as hypertension, diabetes, Parkinson’s disease, and kidney failure. Presence of OH heralds higher mortality and increased incidence of cardiovascular disease, with majority of patients being asymptomatic in normal conditions. In contrast, POTS affects predominantly young women (70–80%) within a range of 15–40 years and is usually accompanied by deconditioning and cognitive impairment. Management of orthostatic intolerance includes both non-pharmacological and pharmacological methods with limited efficacy in severe cases. Empirical treatment with vasoactive, volume-expanding and heart rate controlling drugs for POTS is widely used but rarely fully effective.