How does noradrenaline result in rise of systolic blood pressure even when the cardiac output is decreasing?
Your question involves comparing an observed response to administration of noradrenaline/norepinephrine, which causes vasoconstriction thereby increasing the BP (during both systole &amp; diastole,) to the hemodynamic/pharmacodynamic response of the cardiovascular system as a whole, which is decreased cardiac output &amp; decreased cardiac work.  This is similar to asking why opening a finite water tank eventually slows down even though the pressure increases when you turn on the faucet.