Periodic breathing in the crocodile, Crocodylus niloticus: Consequences for the gas exchange ratio and control of breathing

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Abstract
The ventilatory pattern in the Nile crocodile consists of episodes of breathing, interrupted by periods of breath-holdin, the latter occupying 80% of total time during normal breathing at 25°C. End-tidal gas composition varied with the periodic breathing but Po2 was always high (Po22 low (Pco2E, was very low during the non-ventilatory periods (RE ≃ 0.5), but increased markedly during ventilation. Breathing of hypoxic and hypercapnic gases caused a pronounced decrease in the duration of breath-holds. Hypercapnia decreased breathing frequency during ventilatory periods, but increased tidal volume. The results are discussed in relation to the practice of prolonged breath-holding associated with diving in crocodiles.