The first is the failure in autoregulatory mechanism in the vascular bed. The autoregulation system is a key factor in the pathophysiology of HTN and hypertensive crisis. Autoregulation is defined as the ability of the organs (brain, heart, and kidneys) to maintain a stable blood flow irrespective of alterations of perfusion pressure. If the perfusion pressure drops, the corresponding blood flow decreases temporarily, but it returns to normal values after the next few minutes. In case of autoregulation malfunction, if the perfusion pressure drops, this leads to decrease in blood flow and an increase in vascular resistance. In hypertensive crisis, there is a lack of autoregulation in vascular bed and blood flow and so an abrupt increase of BP and systemic vascular resistance can occur, which often leads to mechanical stress and endothelial injury