Pressurised aerosol inhalers

Pressurised aerosol inhalers (also known as pressurised metered dose inhalers, or by the abbreviations pMDI or MDI) deliver medication via an aerosol.  They were the first type of inhaled device that was produced on a large scale to deliver inhaled therapy to patients with respiratory disease.  It is likely that if you’ve come across someone that uses inhaled therapy then it will be a pMDI device.  This device is always required to be used with a spacer unless a patient has impeccable inhaler technique.

Dry Powder Inhalers

Dry Powder Inhalers, commonly known by the abbreviation DPI, deliver the medication via a dry powder and usually require patients to have a higher inspiratory effort (to trigger release of the medication) than is necessary for an MDI.   DPIs cannot be used with spacers.

Holding chambers or “Spacers”

Holding chambers, more commonly referred to as “spacers” are plastic chambers that are used with MDIs to increase the amount of lung deposition of the aerosol based inhaled drug.  It is an essential accessory with a pMDI, and especially improves drug deposition in the lungs of patients that have particularly poor inhaler technique.  There are various types of spacers and some are compatible with certain inhalers but not others.

Airflow limitation

Airflow limitation is usually measured by a test called spirometry, which assesses a person’s lung function.  A patient will blow in to a mouth piece connected to a machine and the machine will generate numbers that correspond to various functions of the lungs.  The most commonly used measurement to identify airflow limitation is the FEV1 or Forced Expiratory Volume in one second.  This value corresponds to the volume of air that a person can breathe out in one second.

CAT (COPD Assessment Test)

The COPD Assessment Test (CAT) is a questionnaire for people with COPD.  It is designed to measure the impact of COPD on a person’s life, and how this changes over time.  The CAT is very simple to administer, and aims to help clinicians manage a patient’s COPD better.


An exacerbation is defined as a significant flare up of a patient’s chronic illness.  This term is often used in Asthma and COPD when a patient is more breathless or coughs more persistently than usual.  In COPD, the frequency of exacerbations that a patient has can be associated with a poorer prognosis and therefore it is often used to determine how to manage some patients.


The MRC dyspnoea scale is a scoring system to determine how breathlessness impacts on their daily activities.  It is used to help categorise the severity of disease in patients with COPD.  The scale scores patients from one to five: the higher the number, the greater the breathlessness.

  1. Not troubled by breathlessness except on strenuous exercise.
  2. Short of breath when hurrying or walking up a slight hill.
  3. Walks slower than contemporaries on the level because of breathlessness, or has to stop for breath when walking at own pace.
  4. Stops for breath after about 100 m or after a few minutes on the level.
  5. Too breathless to leave the house, or breathless when dressing or undressing.