Ventilatory effects of the single-breath CO2 test, compared with eructation, in cattle.

Objective: To assess the peripheral chemoreceptor-induced ventilatory response to single tidal-breath CO2 (SB CO2) tests, compared with eructations, in 2 breeds of calves.

Animals: 13 conscious unsedated Holstein-Friesian and 8 Belgian White and Blue hypermuscled calves.

Procedure: An SB of +/- 50% CO2 in equal parts of O2 and N2 was inhaled. Ventilatory response was determined from the increase in ventilation (delta Ve) during the first 20 seconds after the test breath or eructation and from the difference in end-tidal PCO2 between the stimulus and preceding control breaths.

Results: Because no difference was found between the 2 breeds of calves, all data were pooled. The increase in Ve peaked during the fifth breath after the SB CO2 test on average, corresponding to a delay of 12.4 seconds. The SB CO2 responses ranged from 0.037 to 0.151 L/min.mm of Hg.m2, with a mean +/- SD of 0.082 +/- 0.032 L/min.mm of Hg.m2 for all calves. The SB CO2 tests, similar to eructations, modified the breathing pattern significantly and in the same direction, by principally shortening expiratory time and increasing mean inspiratory flow. After eructations, Ve peak increase was more important for lower difference in end-tidal PCO2 between the stimulus and preceding control breaths and took place more rapidly than after SB CO2 tests. Accordingly, eructation responses were more marked than SB CO2 responses and averaged 0.925 +/- 0.276 L/min.mm of Hg.m2.

Conclusions And Clinical Relevance: In cattle, the pattern of breathing and ventilation under basal conditions is characterized by a cyclic variability coupled to eructation.