Figure 1.

Study protocol. Each participant completed 3 separate visits a minimum of 48 hours apart. The protocol for each visit was randomized. On each test day, measurements of hemodynamics, end tidal oxygen and carbon dioxide, and cerebral blood flow velocities were obtained for a steady-state period and NVC assessment prior to drug or placebo administration. NVC indicates neurovascular coupling; PE, phenylephrine; and SMTC, S-methyl-L-thiocitrulline.