Effects of Midodrine and Droxidopa on Splanchnic Capacitance in Autonomic Failure

This study investigates how two blood pressure medications — midodrine and droxidopa — affect blood pooling in the belly area in people with conditions that cause low blood pressure when standing up (a condition called neurogenic orthostatic hypotension). **You may be eligible if...** - You are between 40 and 80 years old - You have been diagnosed with a condition like Multiple System Atrophy, Pure Autonomic Failure, or Parkinson's disease - You experience a significant drop in blood pressure when you stand up (dizziness, lightheadedness) due to a nerve problem - You are able to give informed consent **You may NOT be eligible if...** - You do not have a qualifying nervous system condition - You do not experience blood pressure drops when standing - You are unable to safely participate in the study procedures This research may help improve medications that help patients with these nerve disorders stand and move without fainting. Talk to your doctor to see if this trial is right for you.