Time Course of Pulmonary Vascular Response to an Acutely Repetitive Pulmonary Microembolism in Dogs. An Analysis Using Pulmonary Vascular Impedance.

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Abstract
To understand the mechanism leading to progressive pulmonary hypertension, we investigated the time course of vascular response to an acutely repetitive pulmonary microembolism in dogs by using pulmonary vascular impedance. In a normal state, the mean pulmonary arterial pressure (mPAP) was transiently increased by emboli, and the impedance moduli of 0 Hz (= Rin), 1.5 Hz and 3 Hz were slightly increased. A four-element electrical vascular model showed the transient increase in peripheral pulmonary vascular resistance (R2) and inertia, and reduction in compliance (C). In contrast, in a state of a slight pulmonary hypertension, mPAP was continuously increased by the same amount of emboli, and the impedance moduli of both 0 Hz and 3 Hz were significantly increased. By a four-element model, a severe increase in R2 and reduction in C were observed, and these changes continued. Therefore, although the vascular response to pulmonary microembolism basically depends on the degree of mechanical obstruction, this response is thought to be modulated by the responsiveness of pulmonary vessels at that time, which is involved in the alteration in the local characteristics of pulmonary vessels, and/or the recruitment of a new blood flow.

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