3996
Morphometric analysis revealed an increase in the extent of emphysematous changes after 5 months of MS inhalation , which did not significantly change over the following 13 months of study duration , irrespective of whether MS exposure was continued or not .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 None