The sensitivity of a person's cough reflex can be measured by getting them to breathe in (inhale) irritant chemicals. There are different methods by which subjects are asked to inhale these chemicals, either by taking one deep breath in, or by asking them to just continue to take a number of breaths. The purpose of this clinical research study is to see if the coughing responses are different in healthy people and people with respiratory problems that make them cough when they are given these chemicals in these two methods.