Splanchnic Venous Capacitance in Postural Tachycardia Syndrome

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

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

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.

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.