Respiratory and circulatory changes associated with exposure to elevated ambient carbon dioxide (CO2) levels were studied in free-moving Bufo marinus. The buccal cavity, lungs, and systemic arch were cannulated singly or in various combinations. Simultaneous recordings from the lungs and buccal cavity permitted analysis of respiratory rate and pattern, while systemic cannulae provided constant blood-pressure measurements. All experiments were conducted at 22 °C.Normal breathing patterns consisted of continuous buccal 'oscillations' with irregularly occurring lung 'ventilations' and occasional high pressure 'inflations.' On exposure to increased ambient CO2 levels, oscillations decreased, ventilations increased, and inflations predominated, resulting in an overall increase in lung minute-volume. Systemic pressure decreased as ambient CO2 approached 3%, but returned to normal, with an associated increase in heart rate, at the 5% level. It is postulated that the ventilatory and concomitant circulatory responses are mediated by receptors functioning in both the chemoreceptive and baroreceptive modes.

Respiration and circulation were studied in the aquatic apodan amphibian Typhlonectes compressicauda (order Oymnophiona). The animals tolerate the often hypoxic and hypercapnic nature of their habitat by means of large blood volumes (25% body weight), high haemoglobin levels (11.28 g/100 ml blood), and a low P50 (22.2 mmHg (1 mmHg = 133.322 Pa)). The Bohr effect is negligible and the effects of haemoglobin concentration on the CO2 dissociation curve are discussed. Partial pH compensation in induced hypercapnic situations was accomplished. Good separation of oxygenated and deoxygenated blood within the ventricle was shown by serial sampling from both pulmonary and systemic arches.

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