Qualitative Sweat Distribution During Tilt Table Procedure

The investigators' laboratory has conducted an exploratory study of quantitative sweat during tilt table testing over the past year. Some patients with Postural Tachycardia Syndrome (POTS) experience excessive sweating. Patients with syncope (without POTS) have an increase in sweat during their tilt-induced syncopal episode. Increased warmth and sweating can be among the first pre-syncopal symptoms in some individuals. Anxiety can also produce a sweat response, so-called "emotional sweating". Emotional sweating tends to affect the palms, soles, and forehead prominently, while the distribution of orthostatic sweat has not been well-described. The investigators' sweat measure quantifies sweat production, but placement of the sweat capsules is limited to four sites on the arms and legs. An Alizarin Red powder mixture applied to exposed skin is brown in color when dry and red in color when moist. Using Alizarin red, a quantitative sweat measure, and serial photography, the investigators will characterize the sweat distribution in patients with syncope, anxiety, and POTS. Patients will be recruited if they had a sweat response from prior tilt table testing performed in the investigators' laboratory. Consenting patients will wear underwear or bathing suits. The investigators will apply Alizarin Red to all exposed skin below the angle of the mandible. A single sweat capsule will be placed at the right hip. Pre-tilt photos will be taken, and then the patient will be tilted head-upright to seventy degrees. Once sweat begins, serial photos will be taken. The patient will remain in the tilted position until syncope occurs or the Alizarin powder is saturated red. If a sweat response is not prominent and syncope does not occur, the patient will be lowered after 30 minutes. The investigators will use the serial photos to describe the temporal distribution of sweat with each patient. Orthostatic sweat can occur before or after syncope, but based on the investigators' prior quantitative sweat measures, there is always an associated drop in blood pressure. The investigators can distinguish emotional from orthostatic sweat based on the patient's self-report of anxiety/panic, the presence of tachypnea, and the absence of syncope or hypotension. The current study aims to characterize sweat production during tilt testing and distinguish orthostatic and emotional sweat distributions. The primary goal of this study is to compare sweat distributions in patients during syncope (orthostatic sweat) and during anxiety (emotional sweat). The secondary goal is to characterize tilt-induced sweat distributions in POTS patients and compare them to the orthostatic and emotional sweat patterns. The investigators hypothesize that emotional sweat will predominantly affect the palms and soles (forehead sweat will not be measured), while orthostatic sweat will have a truncal predominance. This study is significant because the sweat pattern may help to resolve POTS and syncope phenotypes which will ultimately aid in gene discovery for these disorders.