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Cardiovascular responses to hypoxia and anaemia in the toad Bufo marinus

Johnnie B. Andersen^1,*, Michael S. Hedrick^1,2 and Tobias Wang¹

¹ Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Denmark
² Department of Biological Sciences, California State University, Hayward, CA 94542, USA

View larger version (27K): [in a new window]   Fig. 1. Effects of hypoxia (FIO2=fraction of oxygen in the inspired air) on arterial oxygen levels before and after reducing haematocrit (filled and unfilled circles, respectively). (A) Oxygen concentration ([O2]); (B) haematocrit; (C) arterial oxygen tension (PaO2; 1 mm Hg=133.3 Pa); (D) haemoglobin concentration ([Hb4]); (E) haemoglobin oxygen saturation (HbO2sat) and (F) mean cellular haemoglobin concentration (MCHC). Significant effects of hypoxia within each of the two groups (normal and low haematocrit, respectively) are marked with an asterisk, and significant differences between the groups are marked with a dagger. Data are presented as means ± 1 S.E.M. (N=6).

View larger version (25K): [in a new window]   Fig. 2. Effects of hypoxia (FIO2=fraction of oxygen in the inspired air) on acid—base status before and after reducing haematocrit (filled and unfilled circles, respectively). (A) Arterial pH (pHa); (B) plasma bicarbonate concentration; (C) arterial carbon dioxide tension (PaCO2; 1 mm Hg=133.3 Pa) and (D) Davenport diagram. In the Davenport diagram, an in vitro buffer line previously determined by Andersen et al. (2001) is shown as a dotted line, and isobars for carbon dioxide tension have been added (grey lines). Significant effects of hypoxia within each of the two groups (normal and low haematocrit, respectively) are marked with an asterisk, and significant differences between the groups are marked with a dagger. Data are presented as means ± 1 S.E.M. (N=6).

View larger version (26K): [in a new window]   Fig. 3. Effects of hypoxia (FIO2=fraction of oxygen in the inspired air) on blood flows before and after reducing haematocrit (filled and unfilled circles, respectively). (A,B) Pulmocutaneous blood flow (pc); (C,D) systemic blood flow (sys); (E,F) net shunt fraction (pc/sys) and (G,H) net shunt flow (shunt). The dotted lines represent the condition where there is no net shunt. Significant effects of hypoxia within each of the two groups (normal and low haematocrit, respectively) are marked with an asterisk, and significant differences between the groups are marked with a dagger. B, D, F and H show data for toads with normal [O2] during normoxia, toads with normal [O2] during hypoxia (FIO2=0.10), and anaemic toads during normoxia. Significant differences between normoxic and hypoxic animals are marked with `a', and differences between normoxic and anaemic animals are marked with `b'. Data are presented as means ± 1 S.E.M. (N=6).

View larger version (25K): [in a new window]   Fig. 4. Effects of hypoxia (FIO2=fraction of oxygen in the inspired air) on heart parameters before and after a 50% reduction in haematocrit (filled and unfilled circles, respectively). (A,B) Total cardiac output (tot); (C,D) heart rate (fH); (E,F) stroke volume (VS) and (G,H) systemic blood pressure (1 cm H2O=98.1 Pa). Significant effects of hypoxia within each of the two groups (normal and low haematocrit, respectively) are marked with an asterisk, and significant differences between the groups are marked with a dagger. B, D, F and H show data for toads with normal [O2] during normoxia, toads with normal [O2] during hypoxia (FIO2=0.10), and anaemic toads during normoxia. Significant differences between normoxic and hypoxic animals are marked with `a', and differences between normoxic and anaemic animals are marked with `b'. Data are presented as means ± 1 S.E.M. (N=6).

View larger version (29K): [in a new window]   Fig. 5. Effects of hypoxia (FIO2=fraction of oxygen in the inspired air) on the distribution of blood flows and cardiac parameters on two consecutive days exposure to hypoxia (filled and unfilled circles, respectively). (A) Systemic blood flow (sys); (B) net shunt fraction (pc/sys); (C) pulmocutaneous blood flow (pc); (D) net shunt flow (shunt); (E) heart rate (fH) and (F) stroke volume (VS). The dotted lines represent the condition where there is no net shunt. Significant effects of hypoxia during either the first or second exposure are marked with an asterisk. Significant effects between first and second exposure are marked with a dagger. Data are presented as means ± 1 S.E.M. (N=6).