- Michael Axelsson & CE Franklin 2011 Compar Biochem & Physiol A160:1-8
Elucidating the responses and role of the cardiovascular system in
crocodilians during diving:
fifty years on from the work of C.G. Wilber
In 1960, Wilber in a laboratory-based study described for the first time the
changes in heart rate with submergence in the American alligator, esp.the
marked bradycardia that occurred during forced dives.
This short review summarizes the major advances in our understanding of
diving, and the responses and role of the cardio-vascular system, of
crocodilians during submergence in the 50 yrs since Wilber published his
These advances are attributable in part to the technological advances made
in physiological monitoring devices & wildlife telemetry, that have not only
provided greater elucidation of the hemo-dynamics of the unique crocodilian
cardio-vascular system, but also allowed the natural diving behaviors &
heart rates in free-ranging crocodiles to be recorded.
Of note, telemetric field-based studies have revealed that wild free-ranging
crocodiles typically undertake only short dives, <20 min, yet crocodiles are
also capable of dives of many hours in duration.
In contrast to Wilber's study, dives recorded from free-ranging crocodiles
were found to be accompanied by only a modest bradycardia, highlighting the
often confounding effects associated with captive animals monitored under
More recent studies have also documented the complex central flow & pressure
patterns of crocodilians, including a pulmonary to systemic shunt that can
be initiated by a unique intra-cardiac valve located in the subpulmonary
The role & significance of this cardiac shunt remains controversial, and the
focus of recent lab-based studies.
We contend that elucidation of the role & significance of the cardiac shunt
in crocodilians will only be achieved by monitoring telemetrically the
central cardio-vascular flows & pressures in non-captive animals that are
undisturbed & free-ranging
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