Bronchopulmonary C-fibers modulate the breathing pattern in surfactant-depleted juvenile cats

The aim of this study was to investigate the influence of nonmyelinated C-fibers on the breathing pattern by cooling the vagal nerves to temperatures at which myelinated nerve transmission from pulmonary stretch receptors is blocked (+7 °C) and further at which nonmyelinated fiber input is blocked (0 °C), in anaesthetized spontaneously breathing juvenile cats with normal (LN), surfactant-depleted (LD) and surfactant-treated (LT) lungs. In LN, vagal cooling from +7 to 0 °C decreased respiratory frequency (fR; −8%; p < 0.01), and increased tidal volume (VT; +40%; p < 0.01). In the presence of shallow fast breathing in LD, fR decreased (+38 to +7 °C: −26%; p < 0.015 and +7 to 0 °C: −24%; p < 0.001) and VT increased (+37%; p < 0.049 and +88%; p < 0.016). In LT, fR decreased (+7 to 0 °C: −21%; p < 0.001), whereas VT remained the same at 0 °C (+12%; NS). These findings show for the first time that the activity of bronchopulmonary C-fibers have a prominent role in modulating the breathing pattern in juvenile cats with surfactant-depleted lungs.