Influence of Moderate Vasoconstriction on the Wave Reflection Properties of the Pulmonary Arterial Bed

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Abstract
Increased transmural pressure in the pulmonary arterial bed may reduce vascular input impedance and reduce hydraulic power linked to pulsatile blood flow. Vascular impedance and pulsatile hydraulic power (Wp) levels of isolated perfused rabbit lungs were compared after similar rises of pulmonary arterial pressure (PAp), induced by vasoconstriction or by left atrial pressure (LAp) elevation. Resulting Wp levels were significantly smaller after vasoconstriction than LAp elevation. Wp showed a minimum level at physiologic PAp (about 20 cm H2O) irrespective of the cause of PAp elevation. Pressure pulse wave reflection coefficient (.GAMMA.) calculated for control and test situations approximately doubled after vasoconstriction. Only minor changes in .GAMMA. were found after LAp elevation. Moderate vasoconstriction (resulting PAp .apprxeq. 20 cm H2O) caused a backward traveling pressure wave of high amplitude, appearing in counter-phase to the forward pressure wave at the input site. The total pressure wave amplitude was markedly lowered, resulting in a reduced Wp level. This effect of moderate vasoconstriction may be one reason for the existence of vascular smooth muscles in the pulmonary arteries.