CRI in POTS in Adolescents

The investigators aim to study whether the Compensatory Reserve Index (CRI) (an FDA approved device that assesses intravascular volume) can be used to evaluate severity of Postural Orthostatic Tachycardia Syndrome (POTS) and whether the CRI value has a correlation with severity of psychosocial symptoms and functional impairment associated with POTS.

Autonomic dysfunction (or dysautonomia) describes several medical conditions linked to the autonomic nervous system. One of these is Postural Orthostatic Tachycardia Syndrome (POTS). In pediatric populations, symptoms of autonomic dysfunction include an increase in heart rate when standing up (tachycardia), dizziness, nausea, vomiting, fatigue, headaches, abdominal discomfort, and sleep disturbances. POTS is specifically characterized by orthostatic intolerance and a forty beats per minute (bpm) increase in heart rate upon standing. The etiology of POTS is poorly understood, and there is limited literature on the management of POTS in pediatric populations. In the U.S., POTS is estimated to affect 1-3 million people.

The ability of the CRI algorithm to accurately distinguish individuals with varying tolerances to reduced central blood volume can be attributed to a unique function of the algorithm, which analyzes and compares the entirety of each waveform in a window of time to trend subtle features that correspond with varying degrees of central volume loss. CRI can also detect vascular changes associated with postural orthostatic tachycardia syndrome. CRI will be evaluated in subjects at supine and standing positions along with traditional orthostatic measures.

Following CRI measurements, subjects and their parents will be asked to complete a series of surveys to assess their psychosocial symptoms and functional impairment. The CRI measurement and survey completion will occur over the course of one clinic visit.

Eligibility Criteria:
Inclusion Criteria:

* Adolescent participants must be aged 12 to 21 years (inclusive).
* Each participant must have at one parent/legal guardian who can provide informed consent for the adolescent and participate in the study by completing study questionnaires.
* Moreover, as the majority of study measures are only validated for use in English, only English-speaking patients will be included in this study.

Exclusion Criteria:

* Adolescents will be excluded from the study if they are outside the age range of 12-21 years old
* Adolescents who are wards of the state
* Adolescents who are incarcerated
* Adolescents who are decisionally impaired (i.e., have difficulty understanding the protocol during the consent process, and/or research team member is unsure of individual's ability to correctly identify whether the research study would need to stop or not)
* Adolescents who object at any time to participating in the study
* Adolescents who have a pacemaker
* Adolescents who are taking beta blocker medications
* Adolescents who were were hospitalized in the past month for serious medical conditions affecting their cardiopulmonary system (note, this does not include recent hospitalizations for trauma or burns).
* Adolescents will also be excluded if their parent/legal guardian(s) are unwilling to participate in the study and/or do not have legal custody of the adolescent participant.
* Adolescents who do not speak English will be excluded from the study as majority of the study measures are only validated in English.