31- Exercise induced Asthma

KYJ 31- Exercise induced Asthma.

In this series "knowing your Jargon" we explore in plain English, the meaning of some of the words we throw around as jargon.

Sitting in a high end respiratory lecture one day the speaker (who obviously new their stuff, but was hopeless at sharing the knowledge in any meaningful way), addressed the topic of asthma and the pathophysiology.

One subject that caught my interest was bronchospasm caused by exercise.  Hard physical exercise is a known trigger for asthma, it is not an allergen that sets off the broncho spasm, but breathing itself.

First let's recap Asthma
A chronic disease that is characterised by a narrowed constricted bronchioles (bronchospasm), cough with sputum, wheeze, breathlessness.
Usually triggered by known allergens, eg house dust mites, smoke, pollens, food allergens.

More rarely exercise and sudden change from humid to dry air environments.  This post will focus on the non allergenic triggers being exercise and dry air.

Physiologically we are nasal breathing beings. Our nose anatomy is physiologically crafted to clean, warm and humidify the air we breathe.
Convoluted, moist mucous covered walls of your nasal cavity are densely serviced with shallow blood vessels that, together trap dust and foreign particles (mucous-snot), humidify the air coming in (mucous-snot), and warm the ambient air to body temperature (dense network of capillaries).

At rest, you effortlessly inhale through your nose and by the time this air travels down your trachea and into the lower airways (bronchioles) it is all nice and warm and humidified.

But when you breathe hard and fast because of vigorous exercise initiating mouth breathing, or, when there is a sudden climatic change from humid to dry or air conditioned air, then this optimal warming and humidification of inhaled air is not adequate.

Dry air arrives at the bronchioles where sensors detect the temperature and humidity being too low.  As a reflex, bronchiole smooth muscles and cells lining the inside of the airways, are stimulated to increase blood flow.  This increases perfusion to goblet cells (that secrete sputum), and the overload induces an expectorating cough.
The increase in blood flow to the capillaries lining the bronchioles now results in an increase of capillary blood pressure (hydrostatic pressure), forcing plasma to leak out of capillaries into the interstitial spaces of the bronchioles.  We call this swelling and engorgement, oedema, and as it swells into the bronchiole, it constricts the passage of air causing wheeze and shortness of breath.  The engorgement stimulates the parasympathetic nervous system to activate, which gives rise to smooth muscle constriction (bronchospasm), and further goblet cell secretions.

Sound familiar??  The pathophysiology of asthma, without the trigger being an immune response (Immuniglobulin E allergic ) inflammatory trigger.

Treatment?
Rest for most.
Humidity helps, but to open the airways, and relax those spasming muscles, salbutamol.
To dry up those secretions (atrovent / ipratropium ) or atropine.

Pathophys the ECT4Health way. Hope this helped your understanding of the differences between conventional and exercise /climate induced bronchospasm/asthma.

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