EFFECTS OF PULMONARY-EMBOLISM ON PULMONARY VASCULAR IMPEDANCE IN DOGSAND MINIPIGS

Pigs have been reported to present with a stronger pulmonary vascular reactivity than many other species, including dogs. We investigated th e pulmonary vascular impedance response to autologous blood clot embol ic pulmonary hypertension in anesthetized and ventilated minipigs (n = 6) and dogs (n = 6). Before embolization, minipigs, compared with dog s, presented with higher mean pulmonary arterial pressure (Ppa; by an average of 9 mmHg), a steeper slope of Ppa-flow (Q) relationships, and higher O-Hz impedance (Z(0)) and first-harmonic impedance (Z(1)), wit hout significant differences in characteristic impedance (Zc), and a l ower ratio of pulsatile hydraulic power to total hydraulic power. Embo lic pulmonary hypertension (mean Ppa: 40-55 mmHg) was associated with increased Z(0) and Z(1) in bath species, but the minipigs had a steepe r slope of Ppa/(Q) over dot plots and an increased Zc. At identical (Q ) over dot and Ppa, minipigs still presented with higher Z(1) and Zc a nd 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, w as 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 vas cular resistance and reactivity and adapt to embolic pulmonary hyperte nsion by an increased Zc without earlier wave reflection. These differ ences allow for a reduced pulsatile component of hydraulic power and, therefore, a better energy transfer from the right ventricle to the pu lmonary circulation.