Explain how and why breathing rate varies with exercise. Why- exercise means increased metabolic action, and so decreased oxygen concentration and increased carbon dioxide concentration. The body needs to get more oxygen and get rid of CO2 faster, so it increases breathing rate. The breathing center responds to neural impulses preventing overstretching of the lungs. Symptoms are constriction and swelling of bronchioles, and thus trouble breathing.
Some asthma is also non-allergy related, called intrinsic asthma.