Postural orthostatic tachycardia syndrome (POTS) is a common cause of orthostatic intolerance in adolescents and adults. Compression stockings are commonly recommended as a treatment modality for POTS, but the effects of abdominal and lower extremity compression during tilt table testing have not been measured in adolescent patients. The aims of our study are to compare heart-rate changes and symptom onset during tilt table testing (a) with and without abdomen/lower extremity compression and (b) with abdominal compression only versus lower extremity compression only. During phase 1, 20 adolescents with POTS will undergo up to 10 minutes of tilt without compression (trial #1), a repeat study of up to 10 minutes with full compression (trial #2), and a third study without compression up to 10 minutes (trial #3). Compression will be performed using the non-inflatable Zoex anti-shock garment. During study phase 2, an additional 20 adolescent POTS patients will undergo up to 10 minutes of tilt without compression (trial #1), a repeat study of up to 10 minutes with abdominal compression only [n=10] or lower extremity compression only [n=10] (trial #2), and a third study repeated without compression up to 10 minutes (trial #3). To limit compression to the abdomen only, we will use the Zoex garment strap numbers 4 and 5 (thigh and abdomen) without straps 1-3 (lower extremities). For lower extremity-only compression, we will use Zoex garment straps 1-4 (lower extremity and thigh) without strap 5. Data collected will include mean and peak heart rates and timing of symptoms with each trial. A paired-samples t-test will be used to compare mean heart rates between trials for each study phase. Hazard analyses will be used to assess time-based endpoints.

Inclusion Criteria:

1. Age 12-19 years
2. POTS diagnosis
3. English speaking -

Exclusion Criteria:

1. Somatic, cognitive, or psychiatric disorder that could prevent safe tilt table testing
2. Medications that cannot be stopped/held safely for the procedure, but can cause or exacerbate orthostatic intolerance -