For more detailed information on this module:

• Medical Encyclopedia: "Breathing difficulty"
  U.S. National Library of Medicine & Nationa Institutes of Health
  http://www.nlm.nih.gov/medlineplus/ency/article/003075.htm
  
  
• Mayo Clinic Tools for Healthier Lives: "Shortness of Breath"
  (Mayo Foundation for Medical Education and Research) http://www.mayoclinic.com/print/shortness-of-breath/MY00119/METHOD=print&DSECTION=all