The response of foetal sheep and lambs to pulmonary inflation

Abstract

1. Pulmonary inflation through a tracheostomy consistently produces an inspiratory response or gasp in the foetal lamb. This response is reversibly removed by vagal cooling or xylocaine local anaesthesia to the air passages. It is abolished by bilateral vagotomy. It is therefore suggested that this gasp response involves a reflex whose afferent pathway is in the vagus nerve. 2. This gasp reflex is also found in lambs aged 1 hr to 30 days. 3. Lambs and foetuses possess a cough reflex. 4. A Hering—Breuer inflation reflex can be demonstrated in lambs. 5. The gasp reflex is distinct from either of these last two. 6. The significance of the gasp reflex in pre‐ and post‐natal life is discussed.

Types of afferent nervous activity which may be measured in the vagus nerve of the sheep foetus

“…In this connexion, it is of interest that we were unable to confirm that an increase in intra-tracheal pressure, however sudden, gives rise to a gasp in the foetus (Hughes, Parker & Williams, 1967). We are uncertain how to reconcile this difference in results: it may be that since these workers used air at room temperature with which to inflate the lungs of the foetus, they may have excited receptors sensitive, for example, to changes in temperature.…”

“…The importance of answering this question is enhanced by the observation in the present study and made previously by Dawes (1968) that respiratory movements can be elicited by a reduction in intra-tracheal pressure and abolished by a rise in pressure and that these changes can be abolished after vagotomy. In this connexion, it is of interest that we were unable to confirm that an increase in intra-tracheal pressure, however sudden, gives rise to a gasp in the foetus (Hughes, Parker & Williams, 1967). We are uncertain how to reconcile this difference in results: it may be that since these workers used air at room temperature with which to inflate the lungs of the foetus, they may have excited receptors sensitive, for example, to changes in temperature.…”