Undoubtedly there are many hundreds if not thousands of people with COPD that have switched to an e-cigarette.
There are some important issues with this:
1. It is vitally important that such persons investigate a full range of e-liquid types and brands, to find the option or options that create minimum problems both now and for the future. Some choices could easily create issues, such as the type of base liquid, flavors used, strong flavors or high percentages of flavorings.
2. Some types of COPD present additional risk that needs careful consideration. For example, emphysema sufferers are at increased risk of pneumonia, and this is an extremely serious issue since it may be incurable and lead to death.
3. People with severe COPD, especially emphysema followed by pneumonia, may die. If they are are using an e-cigarette, there is an appreciable risk the fatality may be attributed to e-cigarette use. This has already happened.
For these reasons it is better to be cautious about recommending e-cigarette use to all/any COPD sufferers without reservation. They need to work very closely with their doctor on this. It is of course true that vaping is a better option than continuing to smoke - but simply saying that 'vaping is OK' is not the right answer in these circumstances. It may well be, but COPD sufferers need to be very careful about what they vape, and keeping their medical carer in the loop.
An entirely honest person would almost certainly suggest they try Snus first.
The use of e-cigarettes by those with severe lung disease is not something to be discussed without a full appreciation of the issues. Of course, it all depends on the severity of the condition in the first place - which is why your doctor needs to be involved.