Standing up

Arterial pressure = HR x SV x SVR

1. Increases venous pooling
2. reduced venous return to heart
3. Reduced  stroke volume and cardiac output
4. Reflex sympathetic responses [carotid baroreceptors] ensure maintained blood pressure
   • Reflex tachycardia + vasoconstriction (to maintain status quo)
   • Reduction in vagal activity

Postural hypotension

1. Failure to increase HR
   • Vaso-vagal
   • Fixed heart rate (drugs, heart block)
2. Reduced stroke volume
   • Fixed afterload
   • Aortic stenosis
   • PE
3. Reduced SVR
   • Vasodilators
   • Sepsis
   • Autonomic failure - chronic DM