snoring vs stertor

snoring

noun
  • The action or sound of breathing during sleep with harsh, snorting noises caused by vibration of the soft palate. 

stertor

noun
  • A snoring sound, as for example even during wakefulness in infants with breathing difficulties. 

  • The act of snoring, especially heavy snoring. 

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