Postural tachycardia syndrome (POTS) is the most common chronic cause of postural lightheadedness, and upright confusion afflicting many Americans, mostly young women. Many POTS patients hyperventilate by increasing their depth of breathing that produces tachycardia, alters blood flow and blood pooling in the body and importantly reduces brain blood flow causing "brain fog". In this proposal the investigators will demonstrate in young women that abnormal repeated brief impairment of blood pressure and brain flow just after standing sensitizes the body's oxygen sensor in POTS to respond as if it were in a low oxygen environment causing hyperventilation and its consequences. In this project the investigators will use various drugs that will help to understand the mechanisms that cause POTS in this unique subset of POTS patients who hyperventilate.
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Orthostatic tachycardia
Timeframe: Baseline in all subjects
Orthostatic Blood Pressure Changes
Timeframe: Baseline in all subjects
Orthostatic Changes in Systemic Vascular Resistance
Timeframe: Baseline in all subjects
Orthostatic Blood Volume Changes
Timeframe: Baseline in all subjects
Orthostatic Changes in Segmental Blood Flow
Timeframe: Baseline in all subjects
Orthostatic Changes in Cerebral Blood Flow
Timeframe: Baseline in all subjects
Orthostasis Induced Rate of Breathing
Timeframe: Baseline in all subjects
Orthostasis Induced Depth of Breathing
Timeframe: Baseline in all subjects
Measurement of chemoreflex sensitivity carotid body chemoreflex and central chemoreflex
Timeframe: Baseline in all subjects
Effects of chemoreflex activation on baroreflexfunction and the effects of baroreflex on chemoreflex sensitivity
Timeframe: Baseline in all subjects