National Jewish Medical and Research Center: "Inhaled Medication with a Metered Dose Inhaler (MDI)."
Asthma Society of Canada: "How to Use Your Inhaler."
Science Daily: "New Asthma Inhaler Propellant Effective, But Costlier."
American College of Chest Physicians: "Using Your MDI-Closed Mouth Technique, Patient Education Guide."
American Academy of Allergy, Asthma & Immunology (AAAAI): "Cumulative effects of formoterol administered by a dry powder inhaler;" "Inhalers;" and "Anti-inflammatory effects of inhaled steroids delivered by HFA-MDI vs delivery by dry powder inhaler."
News release, Merck.
Boehringer Ingelheim: "US FDA Expands Approval of Tiotropium Respimat® for Maintenance Treatment of Asthma in Children."
FDA. Prescribing Information: Spiriva Respimat.
Genetics play a role in the development of COPD.  It is more common among relatives of those with COPD who smoke than unrelated smokers.  Currently, the only clearly inherited risk factor is alpha 1-antitrypsin deficiency (AAT).  This risk is particularly high if someone deficient in alpha 1-antitrypsin also smokes.  It is responsible for about 1–5% of cases   and the condition is present in about three to four in 10,000 people.  Other genetic factors are being investigated,  of which many are likely.