VENTILATORY EFFECTS OF THE SINGLE-BREATH CO2 TEST, COMPARED WITH ERUCTATION, IN CATTLE

Objective-To assess the peripheral chemoreceptor-induced ventilatory r esponse to single tidal-breath CO2 (SB CO2) tests, compared with eruct ations, in 2 breeds of calves. Animals-15 conscious unsedated Holstein -Friesian and 8 Belgian White and Blue hypermuscled calves. Procedure- An SB of +/- 50% CO2 in equal parts of O-2 and N-2 was inhaled. Ventil atory response was determined from the increase in ventilation (Delta Ve) during the first 20 seconds after the test breath or eructation an d from the difference in end-tidal Pco(2) between the stimulus and pre ceding control breaths. Results-Because no difference was found betwee n the 2 breeds of calves, all data were pooled. The increase in Ve pea ked during the fifth breath after the SB CO2 test on average, correspo nding to a delay of 12.4 seconds. The SB CO2 responses ranged from 0.0 37 to 0.151 L/min . mm of Hg . m(2), with a mean +/- SD of 0.082 +/- 0 .032 L/min . mm of Hg . m(2) for all calves. The SB CO2 tests, similar to eructations, modified the breathing pattern significantly and in t he same direction, by principally shortening expiratory time and incre asing mean inspiratory flow. After eructations, Ve peak increase was m ore important for lower difference in end-tidal Pco(2) between the sti mulus and preceding control breaths and took place more rapidly than a fter SB CO2 tests. Accordingly, eructation responses were more marked than SB CO2 responses and averaged 0.925 +/- 0.276 L/min . mm of Hg . m(2). Conclusions and Clinical Relevance-In cattle, the pattern of bre athing and ventilation under basal conditions is characterized by a cy clic variability coupled to eructation.