Characterization of the intermittent breathing pattern in Xenopus laevis

Xenopus laevis exhibits an extensive repertoire of breathing patterns during voluntary diving-emergence behaviour. In experiments where animals surfaced to breathe at a blowhole fitted with a pneumotachograph, two noticeably different patterns of breathing were observed. In the first (burst breathing), long periods of diving were periodically interrupted by short visits to the surface when a discrete series of evenly spaced ventilations occurred. On other occasions, the same animal might rise to the surface and begin ventilating its lungs, not in discrete bursts, but intermittently over a long period of time (a breathing bout). Minute ventilation during a breathing burst was more than double that of a bout and represents a more active diving-emergence behaviour on the part of the animal. Regulation of the amount of gas exchanged in both breathing styles appears to be due to manipulation of the temporal pattern of lung ventilations (i.e. the breath-hold durations), rather than to an alteration in the overall depth of breathing; the latter is possible to some extent, however, through adjustments in the composition of individual ventilations.