Fig. 4. The effects of acetazolamide (Az) injection followed by hypercarbia (Pw_CO2=13.6 mmHg) and the rapid lowering of Pw_CO2 (A) on cardiovascular variables in tambaqui Colossoma macropomum, including (B) arterial blood pressure (PDA; N=7-8), (C) systemic vascular resistance (R_s; N=6-7), (D) cardiac output (b; N=7), (E) heart rate (fH; N=8), and (F) cardiac stroke volume (VS; N=7). Data for Pa_CO2 are replotted from Fig. 3 in A for ease of comparison. Acetazolamide was injected at time=0 min, while the onset of hypercarbia and rapid water CO₂ washout are designated by the vertical broken lines. Values are means ± 1 S.E.M. Significant differences from the pre-injection (time= 0 min) or pre-hypercarbic exposure (time=35 min) values are indicated by an asterisk (one-way RM-ANOVA; P values for acetazolamide treatment and hypercarbia, respectively: B, 0.248 and 0.045; C, 0.050 and 0.116; D, 0.016 and 0.134; E, 0.291 and 0.012; F, 0.038 and 0.006). For the rapid lowering of Pw_CO2, significant differences from the initial value (time= 50 min) are indicated by an asterisk or double-arrowhead line (one-way RM-ANOVA with P values: B, 0.281; C, 0.107; D, 0.011; E, 0.042; F, 0.017).