Organization of central respiratory mechanisms in the brain stem of the cat: genesis of normal respiratory rhythmicity.

Abstract

This investigation was designed primarily to study three closely related questions about rhythmic breathing: a) how is apneusis (apneustic respiration) initiated and modified? b) Is the isolated medulla oblongata capable of producing rhythmic respiration? c) What mechanism generates the rhythm of normal breathing? The changes of respiratory pattern were studied in 131 mid-collicular decerebrate cats following serial transections of the brain stem at various levels, vagotomy and elimination of other peripheral receptors. a) It is concluded that a tonically active pontile center produces apneustic respiration, is anatomically and functionally distinct from the medullary inspiratory center, and is almost certainly not a part of the reticular facilitatory system. Afferent impulses from the carotid receptors may influence but do not initiate apneusis. b) The isolated medulla can maintain rhythmic respiration without the influence of spinal or vagal afferents but only under special conditions. However, the medullary respiratory centers are not the pacemakers for normal respiration. c) A new schema is proposed tentatively for the neural organization of normal respiratory rhythmicity. It is suggested that in normal respiration the rhythm originates in the pontile apneustic center with periodic modulation by inhibitory impulses from the pulmonary stretch receptors in the vagus and from the pneumotaxic center in the rostral pons.