Pheochromocytoma and Orthostatic Hypotension

[AZ7]

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So one of the World explanations says, one of the symptoms of pheochromocytoma can be Orthostatic Hypotension , due to low plasma volume.
How exactly is there low plasma volume?

 

[fatonfire]

Postural hypotension due to volume contraction; reduced erythrocyte mass hence reduced plasma vol. Hope this helps

 

[AZ7]

But why is there reduced erythrocyte mass?

 

[faisal 2000]

The orthostatic hypotension and failure of increased peripheral vascular resistance is due to reduced responsiveness of the vasculare to norepinephrine, probably due to down regulation of α-adrenergic receptors resulting from persistent elevation of the physiological agonist norepinephrine

 

[Pholston]

Orthostatic Hypotension due to decreased blood volume caused by persistent vasoconstriction and diminished sympathetic reflex due to down regulation of α-adrenergic receptors.
This is the reason why these patients are infused liters of normal saline as part of pre-operative preparation since they have very low intravascular volume.