Ventilatory behaviors of the toad Bufo marinus revealed by coherence analysis

Abstract

Breathing in amphibians is a remarkably complex behavior consisting of irregular breaths that may be taken singly or in bouts that are used to deflate and inflate the lungs. The valves at the two outlets of the buccal cavity (nares and glottis) need to be finely controlled throughout the bout for the expression of these complex respiratory behaviors. In this study, we use a technique based on the calculation of the coherence spectra between respiratory variables (buccal pressure; narial airflow; and lung pressure). Coherence was also used to quantify the effects of chemoreceptor and pulmonary mechanoreceptor input on narial and glottal valve behavior on normoxic, hypoxic, and hypercapnic toads with both intact and bilaterally sectioned pulmonary vagi. We found a significant reduction in narial coherence in hypoxic vagotomized toads indicating that pulmonary mechanoreceptor feedback modulates narial opening duration. An unexpectedly high coherence between Pl and Pb during non-respiratory buccal oscillations in hypercapnic toads indicated more forceful use of the buccal pump. We concluded that the coherence function reveals behaviors that are not apparent through visual inspection of ventilatory time series.

Why do models of insect respiratory patterns fail?

“…In noisy systems, it often is unclear whether the noise arises from the actions of the animal or from some kind of experimental or methodological noise. Advances in time-series analysis have hardly made in-roads into insect respiratory pattern identification and classification, despite their widespread use in other areas of vertebrate respiration pattern research (Coelho et al, 2003;Levine et al, 2004;Adams et al, 1978). Here, for simplicity, we refer to three broad insect respiratory gas exchange patterns, which lie along an axis characterizing whether the insect closes its spiracles some or most of the time and, if so, whether patterns of closure are periodic.…”