Hirano Y, Ozasa Y, Yamamoto T, Uehara H, Yamada S, Nakagawa K, Ikawa H, Ishikawa K. Hyperventilation and cold-pressor stress echocardiography for noninvasive diagnosis of coronary artery spasm. Journal of the American Society of Echocardiography. 2001 Jun;14(6):626–33. doi: 10.1067/mje.2001.112110.