Recruiting

Phase 2

Observational StudySplanchnic Venous Capacitance in Postural Tachycardia Syndrome

Sponsor:

Vanderbilt University Medical Center

Code:

NCT05375968

Conditions

Postural Tachycardia Syndrome (POTS)

Eligibility Criteria

Sex: All

Age: 18 - 50

Healthy Volunteers: Accepted

Interventions

Measurement of Splanchnic venous capacitance(SVC)done at Baseline and after 90 min of 75 g glucose in Healthy Controls POTS patients

Measurement of Splanchnic venous capacitance(SVC)done at Baseline and after 90 min of 75 g glucose in Healthy Controls

Compare change is SVC and SMA flow due to GIP antagonist GIP(3-30)NH2

Compare change is SVC and SMA flow due to saline

Study Details

Brief summary:

Postural tachycardia syndrome (POTS) affects ≈3 million young people, characterized by chronic presyncopal symptoms characterized by dizziness, lightheadedness, and orthostatic tachycardia that occur while standing. Across-sectional survey found that 25% of these patients complains that meals rich in carbohydrates are among the factors that further exacerbate POTS's symptoms and cause a myriad of gastrointestinal symptoms.

The splanchnic circulation is the largest blood volume reservoir of the human body, storing ≈25% of the total blood volume and contributing to sudden, and large, fluctuations in the stroke volume (SV). The orthostatic changes in systemic hemodynamics are particularly magnified after meals, due to increased blood volume sequestration triggered by the release of gastrointestinal peptides with vasodilatory properties. The purpose of this study is to determine if the worsening orthostatic tachycardia and symptoms after glucose ingestion in POTS patients are due to a greater increase in splanchnic venous capacitance and excessive blood pooling on standing as compare to Healthy controls.

The study will also determine if glucose-induced GIP secretion increases splanchnic venous capacitance, orthostatic tachycardia and worsening POTS postprandial symptoms. For this purpose subjects will be further randomized to either saline versus GIP(3-30)NH2 acute infusion, to measure the changes their splanchnic venous capacitance and superior mesenteric arterial flow before and after a 75-g oral glucose challenge during supine and 45-degree head-up tilt positions (orthostatic challenge) for up to 3 hours.

Conditions

Postural Tachycardia Syndrome (POTS)

Study ID

NCT05375968

Start date

Feb 25, 2023

Status verified date

Sep, 2025

Completion date

Jun 1, 2028

Anticipated

Primary completion date

May 31, 2027

Anticipated

Eligibility Criteria

Sex: All

Age: 18 - 50

Healthy Volunteers: Accepted

Inclusion Criteria:

Between 18 and 50years of age
Cases: Diagnosis of POTS with presyncope symptoms after meals Or

Controls:

With no significant past medical history, non-smokers and not on chronic medications.
Body mass index (BMI) between 18.5 to 29.9 kg/m2
If pre-menopausal women: must have regular menstrual cycle.

Exclusion Criteria:

BMI above ≥30 kg/m2
Irregular menstrual cycle
Intolerance to CPAP.
Chronic use of acetaminophen
Heart problems: myocardial infarction, angina, heart failure, stroke
Undergone any heart related procedures or stents or on pacemaker.
Uncontrolled hypertension.
Type 1 or type 2 diabetes mellitus
Pregnant or breast-feeding women.
Impaired liver function
Impaired Kidney function test.
Anemia (Hematocrit<34%).
Ongoing substance abuse.
Subjects with abnormal EKG
History of seizures.
Diagnosed with neuropathy due to any reason
History of neck surgery.
Smoker,
On statin therapy for high cholesterol
Rheumatoid arthritis.
On oral corticosteroids,
Current infections
Documented of moderate decrease in blood volume

Study Design

Enrollment

50 participants

Anticipated

Allocation

Randomized

Intervention Model

Crossover

Primary purpose

Diagnostic

Interventions and Outcome Measures

Arms

active comparator: Changes in Splanchnic venous capacitance(SVC) before and after a 75-g oral glucose challenge

To compare and measure changes in splanchnic venous capacitance and superior mesenteric arterial flow before and after a 75-g oral glucose challenge during supine and 45-degree head-up tilt positions (orthostatic challenge) for up to 3 hr. between participants with POTS (Postural Tachycardia Syndrome) and Healthy Control group

Various GIP hormones especially GLP-1, GLP-2, glucagon, and other GI hormones before and after a 75-gram oral glucose at different timepoints through out 3 hours of the study visit

placebo comparator: Effect of GIP antagonist GIP(3-30)NH2 Vs Saline on splanchnic venous capacitance on POTS patients

POTS patients who participated in Aim 1, will be and randomized to either saline versus GIP antagonist (GIP(3-30)NH2) in Visit 2.

The changes in their splanchnic venous capacitance and superior mesenteric arterial flow will be measured, before and after a 75-g oral glucose challenge during supine and 45-degree head-up tilt positions (orthostatic challenge) for up to 3 hr.

Notably, changes in venous capacitance will be assessed using segmental impedance to measure the effect of graded positive airway pressure (CPAP) on splanchnic blood volume.

Interventions

Measurement of Splanchnic venous capacitance(SVC)done at Baseline and after 90 min of 75 g glucose in Healthy Controls POTS patients

While segmental bioimpedance is monitored, continuous positive airway pressure (CPAP) will be applied sequentially at 0, 4, 8, 12, and 16 cm H2O for about 30 seconds each. This positive airway pressure will increase the intrathoracic pressure, which is transmitted to the venous circulation. Pressure (CPAP pressure, X axis) - volume (splanchnic vascular volume measured by segmental impedance and expressed as % change from baseline, Y axis) relationships are then constructed to assess for splanchnic venous capacitance

Measurement of Splanchnic venous capacitance(SVC)done at Baseline and after 90 min of 75 g glucose in Healthy Controls

Compare change is SVC and SMA flow due to GIP antagonist GIP(3-30)NH2

Participants with POTS will be randomize to either saline versus GIP(3-30)NH2 acute infusion. We will measure changes in their splanchnic venous capacitance and superior mesenteric arterial flow before and after a 75-g oral glucose challenge during supine and 45-degree head-up tilt positions (orthostatic challenge) for up to 3 hr. Notably, we will assess changes in venous capacitance using segmental impedance to measure the effect of graded positive airway pressure (CPAP) on splanchnic blood volume.

Compare change is SVC and SMA flow due to saline

Primary outcome measure

Change in splanchnic venous capacitance in Postural Orthostatic Tachycardia Syndrome [ Time Frame: Baseline up to 180 minutes post glucose challenge ]
Effect of glucose-induced GIP secretion on splanchnic venous capacitance [ Time Frame: 0-180 mins ]
Effect of glucose-induced GIP secretion on POTS postprandial symptoms. [ Time Frame: 0-90 mins ]

Central Contacts and Locations

Central contacts

Pedro J Ortiz, MD

689-233-2623 pedro.ortiz.saavedra@vumc.org

Meena Golchha, MD

615-322-3447 meenakshi.golchha@vumc.org

Locations

Vanderbilt University Medical Center

Recruiting

Nashville, Tennessee, United States, 37232

Contacts

Cyndya Shibao, MD, MSCI

cyndya.shibao@vumc.org

Cyndya A Shibao, MD, MSCI

6155120956 cyndya.shibao@vumc.org

Principal Investigator:

Cyndya Shibao, MD, MSCI

More Information

Sponsor

Vanderbilt University Medical Center

Last update posted

Dec 5, 2025

Last verified

Sep, 2025

Keywords

Glucose-dependent Insulinotropic Polypeptide (GIP)

Trial information was received from ClinicalTrials.gov and was last updated on 2026-09-10. This information was provided to ClinicalTrials.gov by Vanderbilt University Medical Center on 2025-12-05.