1. Diaphragm contraction as a limiting factor to maximum expiration
2. Bard Philip. Macleod's Physiology in Modern Medicine.9th ed. The C.V. Mosby Company, St. Louis 1941; 540
3. Bard Philip. Medical Physiology.11 th ed. The C.V. Mosby Company, St. Louis 1961; 561
4. Campbell E. J. Moran. The Respiratory Muscles and the Mechanics of Breathing. Lloyd-Luke Ltd., London 1958; 10