Effects of L-NNA and 1400 W on the strength of HPV. Hypoxic ΔPAP values in the absence of L-NNA and 1400 W are identical to those depicted in Figure 1. A. L-NNA-treated hypoxic normocapnia group (n = 5), B. L-NNA-treated hypoxic hypercapnic acidosis (n = 6), C. L-NNA-treated hypoxic hypercapnia without acidosis (n = 5), D. 1400 W-treated hypoxic normocapnia (n = 6), E. 1400 W-treated hypoxic hypercapnic acidosis (n = 5), F. 1400 W-treated hypoxic hypercapnia without acidosis (n = 5) compared to HPV in the absence of L-NNA or 1400 W during 180 min hypoxic ventilation, followed by 10 min ventilation with normoxic normocapnic gas (recovery). ΔPAP: change of PAP referenced to the value at time set at zero. Data are mean ± SEM. *, significant difference (P < 0.05) compared to untreated groups.