Fig. 4. Effects of hypoxia (FI_O2=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 (FI_O2=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).