Wang J-J, Shrive NG, Parker KH, Tyberg JV. Effects of vasoconstriction and vasodilatation on LV and segmental circulatory energetics. Although the hydraulic work generated by the left ventricle (LV) is not disputed, how the work was dissipated through the systemic circulation is still subject to interpretation. Recently, we proposed that the systemic circulation should be considered as waves and a reservoir system (Wk). By combining the arterial and venous reservoirs, the systemic vascular

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... tance can be viewed as a series of resistors, which in sequence are the large-artery resistance, arterial reservoir resistance, the microcirculatory resistance, venous reservoir resistance, and large-vein resistance, and propelling blood through these resistance elements represents resistive losses. We then studied the changes in the fraction of the work consumed by each element when infusing methoxamine (MTX), a vasoconstrictor, and sodium nitroprusside (NP), a vasodilator. Results show that, under control condition, ϳ50% of the LV stroke work was dissipated through arterial reservoir resistance (NP, ϳ36%; MTX, ϳ27%), another ϳ25% was dissipated by the microcirculation (NP, ϳ20%; MTX, ϳ66%), and ϳ20% of work by the large-artery resistances (NP, ϳ37%; MTX, ϳ6%). The energy dissipated by the venous resistances was small and had limited variation with NP and MTX, where the large-vein and venous reservoir resistances shared ϳ1 and ϳ3% of LV stroke work, respectively. Approximately 60% of LV stroke work is stored as the potential energy during systole under control, and the ratio decreases to ϳ45% with NP and ϳ80% with MTX. left ventricle circulatory coupling; systemic vascular resistance; arterial and venous reservoirs Address for reprint requests and other correspondence: J. V. Tyberg, Cardiac