The role of augmented breaths (sighs) in bronchial asthma attacks.

The study is based on plethysmographic, neurophysiological and respiratory mass-spectrographic records established during anaphylactic or histamine-induced bronchial asthma attacks in guinea-pigs. The frequency of occurrence of the augmented breaths (sighs) is correlated with the intensity of the lung deflation reflex (tachypnoea) which arises during the attack. In the acute phase of the asthma attack, the sighs increase in number and reinforce the uneven ventilation which underlies stimulation of the pulmonary deflation receptors. The sigh becomes an essential component of the vicious circle of uneven ventilation and vagal lung deflation reflex induced. This circle is broken in the recovery phase of the asthma attack, during which the sighs decrease in number, as the conditions underlying their occurrence subside; they now lessen the uneven ventilation and by reopening closed lung units promote a return to normal conditions in lung mechanics. It is concluded that augmented breaths, like the asthmatic tachypnoea, are caused by uneven ventilation resulting in pulmonary self-compression and in turn stimulation of the pulmonary deflation (irritant) endings. Some factors which possibly contribute to the elicitation of augmented breaths are discussed.