Chronic Obstructive Pulmonary Disease (COPD) is a persistent lung disease that makes it very difficult to breathe. The airways and the normally 'spongy' lungs themselves are affected. The main treatment is puffers, some which are long-acting (to control persistent symptoms) and some which are short-acting ('rescue' puffers when suddenly feeling short-of-breath). Beyond persisting breathlessness at rest, people with COPD can also experience dangerous lung-attacks which can require urgent care visits or even hospitalization for treatment. Amazingly, although COPD is the third leading cause of death worldwide, and COPD lung-attacks are a leading cause of hospitalization in Canada, investigators are still unsure which combination of puffers is most effective at treating lung-attacks. The main objective is to determine which puffer treatment combination (just short-acting, or both short-acting and long-acting) best opens up the lungs to airflow during COPD lung-attacks. A test called oscillometry, which requires only quiet breathing and is so safe that it is regularly used in children, toddlers and even infants, will be used to measure lung function changes. All eligible people with COPD receiving urgent lung-attack treatment who agree to participate will perform three rounds of oscillometry: before any puffers, after only short-acting puffers, and finally after long-acting puffers are also added on. Any potential evidence of side effects will be collected from the chart. Oscillometry tests will be compared to see which puffer strategy best improves flow in the airways. Part of the reason why this has not been well-studied so far is that the standard breathing test, spirometry, requires multiple rounds of forceful breathing which is very difficult, even distressing, for many people with COPD (at rest, let alone during a lung-attack). No studies have ever properly studied which puffer strategy is most effective for lung-attacks. The investigators have experience and expertise with oscillometry, the most appropriate test in this setting, to answer this pressing question. This research addresses an important treatment knowledge gap for this very common lung disease. These results could influence how patients with COPD around the world are treated during lung-attacks so that they can breathe better, sooner.