BREATH TIMING, VOLUME AND DRIVE TO BREATHE IN CONSCIOUS RATS - COMPARATIVE ASPECTS

In conscious animals, respiratory frequency (f) and tidal volume (VT) vary breath to breath. Examining the average value of variables associ ated with specific bins of another variable, such as breath f, provide s a unique tool to examine respiratory behaviour. In conscious Sprague -Dawley rats respiratory breath timing, tidal volume (VT) and drive (V T/Tr) were characterized using a plethysmograph. In the majority of ra ts at low breath f, expiratory time (TE) exceeded inspiratory time (TI ) and these times became equal as f exceeded 150 breaths/min; there wa s no evidence for TI greater than TE at higher f, as observed in cats and dogs. When VT is normalized per kg, rat breath VT and VT/TI, binne d by breath f, are continuous with those for the cat and non-panting d og at the lowest breath f. Relative to breath f, breath VT and VT/TI i n rats are greater than in normothermic panting dogs (20 degrees C), b ut only slightly greater than those variables in panting dogs in the h eat (30 degrees C). Lower values of breath VT/TI, binned by breath f o r (V) over dot, in cats and dogs are compensated for by a greater TI r elative to the duration of a given breath. This comparative analysis s uggests continuities of respiratory pattern generation among species. (C) 1997 Elsevier Science B.V.