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D. J. Henderson-Smart, P. Johnson^* and Mary E. McClelland

Nuffield Institute for Medical Research, University of Oxford, Headley Way, Headington, Oxford OX3 9DS

1. Direct simultaneous recordings from chronically implanted electrodes in different parts of the diaphragm were made in young lambs in which laryngeal adductor (thyroarytenoideus) and intercostal electromyograms, airflow, tracheal pressure and electrocorticogram and electro-oculograms for behavioural state were also recorded.

2. An asynchrony of diaphragmatic contraction occurred which was dependent on sleep state. The vertebral portion showed maximal post-inspiratory activity while the lateral paratendinous portion usually terminated abruptly with end-inspiration, reciprocating closely with the onset of expiratory laryngeal adductor activity during quiet sleep. The contraction of the sternal portion was similar to the vertebral portion. In active (rapid eye movement) sleep there was no expiratory laryngeal constriction and post-inspiratory activity occurred in all portions of the diaphragm. During the characteristic bursts of rapid breathing in active sleep all post-inspiratory activity disappeared and the diaphragm contracted synchronously.

3. General anaesthesia (Halothane/N₂O or Nembutal) abolished expiratory laryngeal adductor activity and the discharge pattern became similar in all parts of the diaphragm.

4. Intrathoracic vagotomy of Xylocaine blockade below the recurrent laryngeal nerves abolished post-inspiratory activity in all parts of the diaphragm, in contrast to the effect on expiratory laryngeal adductor activity which increased.

5. Sustained `tonic' electromyographic activity was often recorded from the costal and to a lesser extent the paratendinous portion of the diaphragm. This activity related to adjacent intercostal activity:ipsilateral intercostal blockade with local anaesthetic (Xylocaine 1%) abolished both the intercostal and the `tonic' activity of the costal margins of the diaphragm. Conversely ipsilateral phrenic nerve blockade abolished all but the `tonic' activity which related to intercostal activity.

6. Interpretation of the respiratory activity of the diaphragm could not be made adequately from conventionally placed electrodes (i.e. costal, sternal slip or surface) during spontaneous breathing in unanaesthetized lambs. Simultaneous recordings showed that while expiratory flow and duration were actively controlled by expiratory laryngeal adductor activity and the diaphragm, the latter performed asynchronously. While both laryngeal and diaphragmatic expiratory functions were substantially under vagal control, the former increased and the latter decreased with reduced vagal input.

Present address: King George V Memorial Hospital, Camperdown, New South Wales 2050, Australia.