Cerebrovascular Regulation in the Postural Orthostatic Tachycardia Syndrome (POTS)

Abstract

Patients with the postural orthostatic tachycardia syndrome (POTS) have symptoms of orthostatic intolerance despite having a normal orthostatic blood pressure (BP), which suggests some impairment of cere brovascular regulation. Cerebrovascular autoregulation refers to the maintenance of normal cerebral blood flow in spite of changing BP. Mechanisms of autoregulation include myogenic, metabolic and neurogenic vaso · regulation. Beat-to-beat recording of blood-flow velocity (BFV) is possible using transcranial Doppler imaging. It is possible to evaluate autoregulation by regressing ABFV to ΔΒΡ during head-up tilt. A number of dynamic methods, relating ABFV to ΔΒΡ during sudden induced changes in BP by occluding then releasing peripheral arterial flow or by the Val salva maneuver. The ABFV to ΔΒΡ provides an index of autoregulation. In orthostatic hypotension, the autoregulated range is typically expanded. In contrast, paradoxical vasoconstriction occurs in POTS because of an in־ creased depth of respiration, resulting in hypocapnic cerebrovascular constriction, and impaired autoregulation.