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 degrees C) and further at which nonmyelinated fiber input is blocked (0 degrees C), in anaesthetized spontaneously breathing juvenile cats with normal (L-N), surfactant-depleted (L-D) and surfactant-treated (L-T) lungs. In L-N, vagal cooling from +7 to 0 degrees C decreased respiratory frequency (f(R); -8%; p < 0.01), and increased tidal volume (V-T; +40%; p < 0.01). In the presence of shallow fast breathing in L-D, f(R) decreased (+38 to +7 degrees C: -26%; p < 0.015 and +7 to 0 degrees C: -24%; p < 0.001) and V-T increased (+37%; p < 0.049 and +88%; p <0.016). In L-T, f(R) decreased (+7 to 0 degrees C: -21%; p < 0.001), whereas V-T remained the same at 0 degrees 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. (C) 2007 Elsevier B.V. All rights reserved.