Spectral composition of synchronized discharge of phrenic nerve activity in the rabbit and effects of pulmonary afferents.
In anaesthetized rabbits synchronization of efferent phrenic nerve discharge activity (PNA) was investigated by spectrum analysis. During hypercapnia (6-8% end-tidal CO2) in almost all animals the spectrum analysis of PNA during inspiration revealed a bimodal distribution. A broad peak was present at 45.9 +/- 7.7 Hz (MFO peak) whereas a usually well-defined peak with smaller band width was located at 100.3 +/- 17.1 Hz (HFO peak). Increase of hypercapnia promoted the peak amplitude of HFO but had no consistent effect on the amplitude of MFO. Synchronization in the HFO band gradually increased with the progress of inspiration but declined during the last third of inspiration. HFO could be demonstrated to be also present in postinspiratory activity. The amplitude of MFO slowly increased during inspiration becoming strongest at the end of inspiration. The effect of afferent inputs from pulmonary stretch receptors on synchronization of PNA was found to be very weak. Neither withholding inflation during inspiration nor bilateral vagotomy produced substantial changes of MFO and HFO. Tracheal occlusions, however, during inspiration resulted in a slight increase of the power of MFO and HFO, which mainly was due to an overall increase of power. Augmented breaths resulted in a strong shift of the HFO peak to higher frequencies which was accompanied by a dramatic increase of the peak amplitude and a decrease of the peak band width. The presumptive role of the different types of phrenic motoneurons conveying HFO is addressed.
Schmid
K
K
Department of Physiology, University of Mainz, F.R.G.
Böhmer
G
G
D000818:Animals; D006935:Hypercapnia / Q000503:physiopathology; D008168:Lung / Q000294:innervation*; D008722:Methods; D009475:Neurons, Afferent / Q000502:physiology*; D010791:Phrenic Nerve / Q000502:physiology* / Q000503:physiopathology; D011817:Rabbits; D012119:Respiration; D013997:Time Factors