Postural mechanisms in asthma: importance for nocturnal symptoms.

The supine position impairs ventilatory function in patients with ongoing asthma. The response is dual: an immediate decrease on lying down, present in healthy persons as well, and a progressive decrease specific for asthmatics. The changes are counteracted by bronchodilators, but are not linked to a decreased plasma adrenaline level when supine. The progressive decrease is tentatively explained by an increased vagal tone induced by the resting body position, and is likely to be a key factor in nocturnal asthma.