practical nurse vs registered nurse

practical nurse

noun
  • A person who is certified to provide custodial care such as help in walking, bathing, and feeding. 

registered nurse

noun
  • A professional nurse who is a licensed graduate of a university or college of nursing who has successfully passed an examination such as NCLEX-RN. 

How often have the words practical nurse and registered nurse occurred in a corpus of books? (source: Google Ngram Viewer )