Effects of pulmonary embolism on pulmonary vascular impedance in dogs and minipigs

Pigs have been reported to present with a stronger pulmonary vascular reactivity than many other species, including dogs. We investigated the pulmonary vascular impedance response to autologous blood clot embolic pulmonary hypertension in anesthetized and ventilated minipigs (n = 6) and dogs (n = 6). Before embolization, minipigs, compared with dogs, presented with higher mean pulmonary arterial pressure (Ppa; by an average of 9 mmHg), a steeper slope of Ppa-flow (Q) relationships, and higher 0-Hz impedance (Z0) and first-harmonic impedance (Z1), without significant differences in characteristic impedance (Zc), and a lower ratio of pulsatile hydraulic power to total hydraulic power. Embolic pulmonary hypertension (mean Ppa: 40-55 mmHg) was associated with increased Z0 and Z1 in both species, but the minipigs had a steeper slope of Ppa/Q plots and an increased Zc. At identical Q and Ppa, minipigs still presented with higher Z1 and Zc and a lower ratio of pulsatile hydraulic power to total hydraulic power. The energy transmission ratio, defined as the hydraulic power in the measured waves divided by the hydraulic power in the forward waves, was better preserved after embolism in minipigs. No differences in wave reflection indexes were found before and after embolism. We conclude that minipigs, compared with dogs, present with a higher pulmonary vascular resistance and reactivity and adapt to embolic pulmonary hypertension by an increased Zc without earlier wave reflection. These differences allow for a reduced pulsatile component of hydraulic power and, therefore, a better energy transfer from the right ventricle to the pulmonary circulation.