The purpose of this research study is to determine how vasopressors affect a measure of how
intravenous fluid is administered in people undergoing surgery who have low blood pressure
called Pulse Pressure Variability (PPV). This study will recruit human subjects to undergo
simulated hypovolemia called Lower Body Negative Pressure (LBNP) and will receive
phenylephrine and placebo, while PPV will be measured in both conditions. This research will
help anesthesiologists learn more about how to use PPV in patients undergoing surgery and who
need vasopressors.