To understand more about COPD, we recommend that you start with Wikipedia due to its extensive editing and 214 citations. That article is found in full at https://en.wikipedia.org/wiki/Chronic_obstructive_pulmonary_disease and partially included here.
If you want to go deeper you can download one of the primary prevention articles by the American Journal of Respiratory and Critical Care Medicine. You can download the PDF version from here by clicking this link.
If you’d like to look up a few other authorities on the subject, here are some of the top recommended sites. They are a little easier to read and more summarized than Wikipedia or the PDF article above.
In alphabetical order these references are:
AMERICAN FAMILY PHYSICIAN – https://www.aafp.org/afp/2017/0401/p433.html This article is from 2017 but it has been corrected recently and is still valid.
BMC Part of Springer Nature – https://copdrp.biomedcentral.com/articles has an article in 2017 that relates asthma to COPD and shows how they overlap. You can download the PDF article on the subject here.
COPDFOUNDATION – https://www.webmd.com/lung/copd/default.htm Volume 7, Issue 4 in 2020 is an excellent article, but sometimes not available. Check here to see if the journal is up and available on the internet https://journal.copdfoundation.org/
MAYO CLINIC – https://www.mayoclinic.org/diseases-conditions/copd/symptoms-causes/syc-20353679
MEDLINEPLUS – https://medlineplus.gov/copd.html
NATIONAL HEARTH, LUNG, AND BLOOD INSTITUTE – https://www.nhlbi.nih.gov/health-topics/copd