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A deep inspiration from functional residual capacity to total lung capacity, performed at a low flow rate by a group of 40 unselected adult patients with asthma, yielded an immediate and transient increase (71 per cent, P smaller than 0.001) in specific airway resistance. In 2 of the 40, deep inspiration provoked an attack of asthma. The effect of deep inspiration can be attributed to a vagal bronchoconstrictor reflex, because it was prevented or decreased in most of the cases by inhalation of an anticholinergic drug. Beta-adrenergic blockade by propranolol potentiated in a minority of subjects the bronchoconstrictor response to deep inspiration. Deep expiration also induced a bronchoconstrictor effect, which was weaker than that of deep inspiration. It follows that functional studies of asthmatics may be biased if the technique requires maximal respiratory maneuvers.
Gayrard et al. (Tue,) studied this question.