The Influence of Pulmonary Blood Flow Rate on Vascular Input Impedance and Hydraulic Power in the Sympathetically and Noradrenaline Stimulated Cat Lung

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Abstract
The influence of sympathetic nerve stimulation (NS) and .alpha.-adrenergic receptor stimulation (.alpha.S) on pulmonary vascular input impedance and hydraulic power output of the right heart during variations of cardiac output (CO) was investigated. An open chest cat preparation was used. Pulsatile pressure and flow in the pulmonary artery were measured by high frequency response transducers. Vascular resistance (VR) was inversely dependent on CO, but input impedance of the unstimulated lung was not influenced by CO variations. NS or .alpha.S increased VR and input impedance significantly. The relation pulsatile hydraulic power/total hydraulic power (Wp/Wt) increased 40%, indicating that such stimulation has larger relative influence on impedance than on resistance. The reduction of arterial compliance during NS (maximal stimulus) was calculated to be 60%, independent of CO. Input impedance during NS or .alpha.S was reduced by CO elevations, probably because the concomitant distension of the arterial bed, reduced arterial resistance and inertance. The ratio Wp/CO, pulsatile hydraulic power lost/ml mean arterial flow, was flow dependent both in control and stimulated conditions. Wp/CO was positively correlated to CO in control condition and weakly negatively correlated to CO during stimulation. At high CO the arterial vessels could be stimulated and stiffened without much extra load on the right heart.