Page 89 in: Dr. Kevin Lau. The Complete Scoliosis Surgery Handbook for Patients: An In-Depth and Unbiased Look Into What to Expect Before and During Scoliosis Surgery. Health In Your Hands. ISBN978-9810785925.
Page 460 in: Konrad E. Bloch, Thomas Brack, Anita K. Simonds (2015). ERS Handbook: Self-Assessment in Respiratory Medicine. European Respiratory Society. ISBN978-1849840781.{{cite book}}: CS1 maint: multiple names: authors list (link)