[1] Thomas Jefferson Univ, Jefferson Headache Ctr, Dept Neurol, Philadelphia, PA USA
[2] Univ Calif Irvine, Sch Med, Irvine, CA USA
[3] Univ Calif Irvine, Dept Phys Med & Rehabil, Irvine, CA USA
[4] Univ Mississippi Univ Hosp, Dept Anesthesiol, Jackson, MS USA
[5] Univ Pittsburgh, Dept Anesthesiol, Pittsburgh, PA USA
[6] Univ Calif Irvine, Dept Anesthesiol & Perioperat Care, Orange, CA USA
[7] Univ Calif San Diego, Ctr Pain Med, Dept Anesthesiol, La Jolla, CA 92037 USA