Respiratory Pathophysiology 3

Over halfway there!

One more point about diagnosis before moving onto treatment: there is a subjective scale that may also be used to assess the level of disability. This scale is called the MRC Dyspnea Scale, and goes from Grade 1 to Grade 5, with Grade 1 being basically normal and Grade 5 being quite severely impaired. It basically goes like this:

1. Breathless with strenuous exercise (normal)
2. Short of breath when hurrying on the level or walking up a slight hill (mild)
3. Walks slower than people of the same age on the level or stops for breath while walking at own pace on the level (moderate)
4. Stops for breath after walking 100 yards (moderate)
5. Too breathless to leave the house or breathless when dressing (severe)

Now time for the treatment!

First, a word on acute exacerbations of COPD. As you can imagine, getting some kind of respiratory infection affects people with COPD more than healthy people. Part of this is because of the usual vicious cycle that surrounds COPD: people with COPD are often breathless, so they don't want to exercise a lot, so their lungs become deconditioned and so they become even more breathless. When you're sick, you want to exercise even less, so the vicious cycle is maintained more strongly. Hence, it is imperative that people with COPD remain up-to-date with their vaccinations, especially for respiratory illnesses such as influenza.

Now onto day-to-day treatment! Quitting smoking, as I've emphasised in my previous two posts, is the #1 thing you can do for your lungs. Aside from that, exercise programs and education to improve patients' self-management of COPD are important at all stages of COPD. As-needed short-acting bronchodilators are often prescribed, and as the severity increases more medications may be added, from long-acting bronchodilators to inhaled corticosteroids. In very severe cases, oxygen therapy and even surgery may be done. Surgery includes lung deflation or transplants, but as the success rate isn't all too great, surgery is used as a last-case resort.

Lastly just a quick refresher on some basic physiology and pharmacology concepts. Acetylcholine (ACh), the primary neurotransmitter of the parasympathetic nervous system, is mainly responsible for airway narrowing. Hence airway narrowing can be blocked by administering anticholinergics. Adrenaline and noradrenaline, the primary hormone and neurotransmitter of the sympathetic nervous system, are mainly responsible for airway relaxation and widening through their actions on β₂ receptors. Hence β₂ adrenergic agonists can cause the airways to widen. Remember, airway radius is very important: resistance is proportional to 1 divided by the radius to the power of 4. Hence even small changes in radius will lead to large changes in resistance.

Three short posts down, only one to go!