Inflammation plus a hair-trigger
Asthma starts with a chronically inflamed airway lining. Even between attacks, the wall is mildly swollen and primed. On top of that sits airway hyperresponsiveness — the muscle is so twitchy that things which would not bother most people (cold air, exercise, pollen, dust, a viral cold, smoke) make it clamp down. The narrowing of an attack is therefore two things at once: a fast muscle spasm and a slower swelling-plus-mucus.
In many people the inflammation is driven by a particular white blood cell, the eosinophil — so-called eosinophilic inflammation. This matters more than it sounds: it predicts who will respond beautifully to inhaled steroids and, in severe cases, who might benefit from newer targeted treatments. We will pick that thread up in the inhaler guide.
Anatomy of an attack
An asthma exacerbation — an attack — usually unfolds in a recognisable order:
- A trigger lands on the primed airway and the smooth muscle contracts — bronchospasm. The chest tightens within minutes and a wheeze appears.
- Over the next hours the wall swells and mucus plugs the smaller tubes — this “late phase” is why an attack can worsen again after the spasm eases.
- Breathing out becomes slow and incomplete; the person uses accessory muscles, speaks in short phrases, and air begins to trap.
- A reliever inhaler relaxes the muscle and, in most attacks, the airway opens back up — the hallmark of reversible airflow obstruction.
Reversibility, measured
What turns the story above into a *diagnosis* is showing that the obstruction can open up. Two simple tools do this. A peak flow meter measures how hard you can blow; asthma's readings swing — lower in the early morning, higher after a reliever — and that variability is itself a clue. More formally, bronchodilator reversibility testing measures airflow before and after a reliever and looks for a meaningful jump.
Bronchodilator reversibility (spirometry): FEV1 before reliever : 2.10 L FEV1 after reliever : 2.55 L Change = 2.55 - 2.10 = 0.45 L (450 mL) % change = 450 / 2100 = +21% Interpretation: a rise of >= 12% AND >= 200 mL is counted as significant reversibility -> supports asthma. (Here: +21% and +450 mL -> clearly reversible.)