Studies

This page publicizes the research of DINET's medical advisors. If you are a physician who would like your research included on this page, please contact DINET at: staff@dinet.org.

Studies are provided for informational purposes only. DINET cannot guarantee satisfaction from any of the following research studies.

- Local Vasoconstriction in Postural Tachycardia Syndrome
- Pathophysiology and Therapy of Orthostatic Intolerance
- Hyperpnea in Postural Tachycardia
- Autonomic Dysfunction in IBS

Local Vasoconstriction in Postural Tachycardia Syndrome

We are seeking patients aged 15-29 years old with postural tachycardia syndrome (POTS) for an investigation of abnormalities of regulation of blood flow. Many people are unable to remain upright for long because of symptoms such as dizziness, nausea and headache. This may occur on a day-to-day basis and may severely compromise lifestyle. The most common cause of this condition is the postural tachycardia syndrome (POTS). POTS is defined by an abnormal increase in heart rate (“tachycardia”) and symptoms that occur when upright (therefore “postural”).

POTS has many causes, all related to an abnormal decrease in the amount of blood returning to the heart. It is a problem in blood flow regulation. Blood flow regulation is partly due to the autonomic nervous system and partly due to local factors. It is these local factors that we are currently studying.

Your own doctor can rule out other illnesses which can produce similar symptoms. In addition you may have seen a cardiologist, a neurologist, or an endocrinologist. Tests such as tilt table tests may have already been performed. Some of these tests may be repeated.

However, we will perform other minimally invasive tests that are not ordinarily available to your doctor. They are, however, all approved ways of measuring how blood vessels work. The tests performed during the study may help us determine what treatment is best for you.

If you would like to take part in this study, please read further at our website, www.syncope.org where there is a link to detailed study information. Then, please get in touch with us. The study coordinator will contact you to arrange for an appointment for the study. Testing lasts two days. The study may help to determine the specific biochemical causes of POTS and will point towards improved medical therapy for young patients.

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Pathophysiology and Therapy of Orthostatic Intolerance

Studies to identify the role of the brain, the autonomic nervous system and the vasculature in Orthostatic Intolerance

All participants are adults. Blood pressure and heart rate are measured lying down and standing at regular intervals. Blood samples are drawn for hormones affecting blood pressure control. Some studies involve medication administration.

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Hyperpnea in Postural Tachycardia

Study Purpose: In this proposal we address the clinical problem of hyperpnea in orthostatic intolerance and propose a line of investigation which we hope will lead to better understanding of autonomic cardiovascular regulation in postural tachycardia syndrome.

We are seeking patients aged 18-29 years old with postural tachycardia syndrome (POTS) who may benefit from an investigation of abnormalities of regulation of  respiration and sympathetic nervous system regulation. Many people are unable to remain upright for long because of symptoms such as dizziness, nausea and headache or fainting. We and others have now shown that there is frequent upright increased breathing and shortness of breath in many POTS patients. This may occur on a day-to-day basis and may severely compromise lifestyle. The most common cause of this condition is the postural tachycardia syndrome (POTS), which is believed to affect at least a million Americans. POTS is defined by an abnormal increase in heart rate (“tachycardia”) that occurs when upright (therefore “postural”). POTS has many causes and we are attempting to determine the precise biochemical basis for POTS in patients.

We hypothesize that excessive baroreflex unloading during orthostatic stress (upright positioning) is the initiating event in POTS which results in two additional physiological consequences leading to hypocapnic hyperpnea (low carbon dioxide caused by markedly increased ventilation): a) reduced inhibition of chemoreceptor activity centrally and b) frank stimulation of peripheral chemoreceptor activity due to sympathetically induced reductions in blood flow to the carotid body. Increased chemoreceptor activity leads to hyperpnea which activates pulmonary stretch receptors. 

Our study will determine how often respiratory abnormalities occur in POTS and their relationship to excessive activation of the sympathetic nervous system, the branch of the autonomic nervous system that regulates blood flow and cardiac contraction.  Specific causes for POTS may vary from patient to patient. Patients will be compared to healthy control subjects. If we know the specific mechanism, we may be able to offer specific treatment to specific patients.

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Autonomic Dysfunction in IBS

Irritable Bowel Syndrome (IBS) is a common yet poorly understood category of disease. One reason for the difficulty in treating patients arises from the heterogeneous nature of IBS pathophysiology. Understanding IBS is important to understanding normal physiology of vascular control and its relationship to the elicitation of gastrointestinal symptoms that are associated with IBS. The goals of this study are therefore to further our understanding of the relationships between the gastrointestinal system and the autonomic nervous system.

We are seeking 3 different populations;  all adolescents and young adults aged 14-19 years with 1) patients with IBS and autonomic symptoms such as excessive sweating, pallor and lightheadedness; 2) patients with IBS without autonomic symptoms and 3) healthy age and sex-matched control subjects without IBS and autonomic symptoms. The determination of IBS will be made according to the Rome III criteria.

We hypothesize that generalized sympathetic responses are reduced in all patients with IBS, regardless of presentation of autonomic symptoms. To test this,  we will measure blood volume and we will continuously measure heart rate and blood pressure and assess peripheral and segmental blood flow using segmental impedance plethysmography to ask the following question: 

We also hypothesize that subjects with IBS and autonomic symptoms have increased evidence of autonomic dysfunction and specifically increased splanchnic blood flow and splanchnic blood volume during orthostatic challenge. To test this we will measure various aspects of cardiovascular control and response when subjects are placed upright at an angle of 70^o for a maximum of 10 minutes.

The proposed studies are anticipated to provide useful information regarding the status of autonomic function exhibited by subjects diagnosed with IBS and the cause of their pain. It is anticipated that these differences will likely be exhibited by IBS patients who describe  “autonomic” symptoms such as lightheadedness, sweating and pallor that may accompany their gastrointestinal symptoms, rather than by IBS patients without these accompanying symptoms. These subjects may be shown to have differences in heart rate variability or blood pressure variability.  This may also manifest itself as differences in the way in which IBS patients can regulate changes in blood distribution during the imposition of an orthostatic challenge. 

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