The respiratory system in varanid lizards: Determinants of O2 transfer

Peter B. Frappell, Timothy J. Schultz, Keith A. Christian

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

Varanids in general exhibit greater aerobic capacities than other lizards. In a similar approach to the extensive investigations undertaken in mammals, the respiratory system in varanids is examined in terms of oxygen transfer from the air to the blood during rest and sustained locomotory activity. The parameters controlling the transfer of O2 through the various steps of the respiratory system are appropriate to meet the maximum demands for oxygen with one possible exception, circulatory convection. Ventilatory convection is maintained during maximal aerobic locomotion ensuring adequate pulmonary ventilation and the protection of alveolar PO2. Little evidence exists to indicate a mechanically imposed constraint to breathe and the possibility of a gular pump acting to assist ventilation, as a general feature of varanids remains to be determined. Alterations in the relative contributions of the ventilation-perfusion ratio, pulmonary diffusion, diffusion equilibrium and right-left shunts preserved the alveolar-arterial PO2 difference, ensuring that arterial oxygenation was maintained. In those species where increases in cardiac output were limited, maximum O2 transfer was achieved through increased extraction of oxygen at the tissues. Overall, the interrelationship of adjacent steps in the respiratory system ensures that one step cannot become limiting. Compensatory changes occur in various parameters to offset those parameters that are 'limited'. The high aerobic activity of varanid lizards would not be achievable without a compensated circulatory convection.

Original languageEnglish
Pages (from-to)239-258
Number of pages20
JournalComparative Biochemistry and Physiology - A Molecular and Integrative Physiology
Volume133
Issue number2
DOIs
Publication statusPublished - Oct 2002
Externally publishedYes

Keywords

  • Excercise
  • Locomotion
  • Lung diffusion
  • Oxygen affinity
  • Oxygen transport
  • Reptile
  • Respiratory system
  • Varanid
  • Ventilation

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