This is an observational study to deeply phenotype the disorder of POTS using multiple testing modalities.

This comprehensive multimodality deep phenotyping will improve the diagnostic approach, inform the development of new treatments, and allow the targeting of therapies to specific POTS patients. The investigators will further identify the diagnostic tools, biomarkers, and clinical outcome measures most relevant to defining the disorder in clinical practice.

The specific aim is to (1) Define clinical POTS classifications from multimodal clinical and laboratory data, (2) address exercise tolerance in POTS using metabolomic assessments, (3) evaluate novel POTS-specific patient outcome measures and (4) evaluate one year outcome data for POTS

Specific research tests will include blood work (for immunophenotyping and neurohormonal assessments), autonomic function testing, skin biopsy (to evaluate intraepidermal nerve fiber density), CO (Carbon Monoxide) rebreathing (for quantitative measurement of plasma volume and red blood cell mass), patient surveys (to characterize symptom profile and disease impact). Blood biosamples will be stored as a repository for future research questions.

Inclusion Criteria:

POTS Patients

• Age ≥ 14 years, able to provide informed consent (assent with parental consent for age < 18) and comply with procedures
• Meets consensus criteria for POTS: (1) sustained increase in heart rate ≥ 30 bpm above supine baseline within 10 min of quiet standing or upright tilt (≥ 40 bpm in individuals 12 to 19 years of age) OR sustained upright HR (heart rate) >120 bpm, (2) absence of orthostatic hypotension, (3) symptoms with standing that improve with sitting or lying down, (4) resting supine heart rate < 100 bpm, (5) orthostatic symptoms present for at least 6 months
• Stable oral medication regimen for at least 14 days

Non-POTS Control Patients

• Healthy women, age 18 - 30 years, able to provide informed consent and comply with study procedures
• Does NOT meet consensus criteria for postural tachycardia syndrome
• No symptoms of orthostatic intolerance or dysautonomia. No history of other major medical disorder
• Resting supine heart rate < 100 bpm

Exclusion Criteria:

None of the following exclusion criteria:

• Use of amphetamine-type stimulants, diuretics, selective norepinephrine reuptake inhibitor, anticholinergic medications (including tricyclic antidepressant medications), fludrocortisone, desmopressin in past 14 days
• Use of other autonomic drugs (adrenergic agents, pyridostigmine, droxidopa, triptans, ivabradine) in past 48 hours
• Currently receiving IVIG (Intravenous immunoglobulin), subcutaneous IgG (Immunoglobulin G), or any investigational medication (in past year)
• Infusion of iv fluids in past 7 days
• History or evidence of another condition explaining symptoms or orthostatic tachycardia (e.g. structural heart disease, CSF (Cerebrospinal fluid) hypovolemia, or severe traumatic brain injury)

POTS patients and Normal Control