PULMONARY VASCULAR-RESISTANCE IN DOGS AND MINIPIGS - EFFECTS OF HYPOXIA AND INHALED NITRIC-OXIDE

The pig has been reported to present with a stronger hypoxic pulmonary vasoconstriction than many other species, including the dog, but it i s not known whether this is associated with a different longitudinal p artitioning of pulmonary vascular resistance (PVR). We investigated th e relationships between cardiac output ((Q) over dot) and mean pulmona ry artery pressure (Ppa) minus occluded Ppa (Ppao), and effective pulm onary capillary pressure (Pc') minus Ppao, in seven minipigs and in se ven dogs in hyperoxia (FIO2 0.4) and hypoxia (FIO2 0.1), first without , then with the inhalation of 80 ppm nitric oxide (NO) to inhibit any reversible component of PVR. Pc' was estimated from the Ppa decay curv e following pulmonary artery balloon occlusion. In hyperoxia, minipigs compared to dogs had (Ppa - Ppao>/(Q) over dot and (Pc'-Ppao)/(Q) ove r dot plots shifted to higher pressures. Hypoxia at each level of (Q) over dot increased Ppa - Ppao in minipigs more than in dogs, and Pc'-P pao in minipigs only. Inhaled NO reversed hypoxia-induced changes in ( Ppa - Ppao)/(Q) over dot and (Pc' - Ppao)/(Q) over dot plots. We concl ude that the minipig, compared to the dog, presents with higher PVR an d reactivity including vessels downstream to the site of Pc' as determ ined by the arterial occlusion technique. (C) 1998 Elsevier Science B. V. All rights reserved.