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Oxygen transfer during aerobic exercise in a varanid lizard Varanus mertensi is limited by the circulation

Peter Frappell^1,*, Tim Schultz² and Keith Christian²

¹ Department of Zoology, La Trobe University, Melbourne, Victoria, 3086, Australia
² School of Biological Sciences, Northern Territory University, Darwin, NT 0909, Australia

View larger version (16K): [in a new window]   Fig. 1. A recording of gaseous washouts obtained during exercise in an animal rebreathing a mixture of He, CO and air. The initial fluctuations and sudden decrease in He represents breath-by-breath change in He as it is mixed with alveolar gas. Helium decreases to a stable concentration whereas CO continuously diffuses from alveolar gas to blood, causing a decrease of alveolar FCO. The concentration of CO relative to He (rel-FCO) changes exponentially with time such that a plot of ln(rel-FCO) versus time yields a linear relationship, shown as the solid line fitted through the data after He has stabilized.

View larger version (16K): [in a new window]   Fig. 2. Rate of oxygen consumption (O2) at rest and during maximum levels of sustained aerobic exercise on a treadmill for V. mertensi. The large solid symbols represent data collected during experimental runs, the small symbols connected by dashed lines represent data obtained pre- (small closed circles) and post-surgically (small open circles) with animals on the treadmill. Values are means ± 1 S.D. (N=6).

View larger version (12K): [in a new window]   Fig. 3. (A) Typical breathing pattern obtained during rest (pre-exercise) and exercise in V. mertensi. (B) A spirogram for rest (open symbols) and exercise (closed symbols) that shows the changes in volume and timing that occur with exercise. Note that each breathing cycle starts with expiration (downward deflection), followed by an inspiration and a post-inspiratory pause. Values are mean ± 1 S.D. (N=5).

View larger version (15K): [in a new window]   Fig. 4. Values obtained for O2, E, E/O2 and PAO2—PaO2 during rest, exercise and recovery in V. mertensi. Changes in O2 were closely matched by changes in E such that E/O2 was maintained. PAO2—PaO2 was maintained at resting values during exercise and the first 2 min of recovery. Values are means ± 1 S.D. (N=5). *Significant difference from the value at rest.

View larger version (39K): [in a new window]   Fig. 5. Influence of exercise on arterial and venous PO2 and O2 content (solid symbols) in relation to the hemoglobin oxygen dissociation for V. mertensi. Values are means ± 1 S.D. (N=6). The open symbols are actual measured values of PaO2 and CaO2 determined at rest. The curve labelled `Exercise' has been adjusted according to pHv and the Bohr effect (see Results). The right panel is a graphical representation of the Fick principle showing the relative contributions of cardiac output (tot) and arterial—venous O2 content difference (CaO2—CO2) to O2 (the shaded area) during rest (cross hatch) and exercise (stippled).