Orthostatic hypertension is a medical condition consisting of a sudden and abrupt increase in blood pressure (BP) when a person stands up. Orthostatic hypertension is diagnosed by a rise in systolic BP of 20 mmHg or more when standing. Orthostatic diastolic hypertension is a condition in which the diastolic BP raises to 98 mmHg or over in response to standing, but this definition currently lacks clear medical consensus, so is subject to change. Orthostatic hypertension involving the systolic BP is known as systolic orthostatic hypertension. If affecting an individual's ability to remain upright, orthostatic hypertension is viewed as a form of orthostatic intolerance. The body's inability to regulate BP can be a type of dysautonomia. Baroreflex and autonomic pathways normally ensure that blood pressure is maintained despite various stimuli, including postural change. The precise mechanism of orthostatic hypertension remains unclear, but alpha-adrenergic activity may be the predominant pathophysiologic mechanism of orthostatic hypertension in elderly hypertensive patients. Other mechanisms are proposed for other groups with this disorder. A prevalence of 1.1% was found in a large population study. The risk of orthostatic hypertension has been found to increase with age, with it being found in 16.3% of older hypertensive patients. Causes The causes of this condition are not well understood, but research suggests that it may be caused by a combination of hemodynamic and neurohumoral factors. Some studies have found that orthostatic hypertension may be caused by increased vascular resistance, possibly due to excess plasma shifts or increased blood viscosity. Other studies have suggested that it may be caused by a reduction in cardiac preload, or an increase in venous pooling. Research suggests that it may be caused by an overshoot in neurohumoral adjustments to standing. Some studies have found that patients with orthostatic hypertension have normal levels of venous plasma norepinephrine, but that these levels increase excessively upon standing. However, other studies have not found elevated levels of norepinephrine in patients with orthostatic hypertension compared to hypertensive controls. These findings suggest that the causes of orthostatic hypertension may be multifactorial and more research is needed to fully understand the underlying mechanisms. Signs and symptoms Mild or moderate orthostatic hypertension may present without any symptoms other than the orthostatic hypertension BP findings. More severe orthostatic hypertension may present with the typical symptoms of hypertension. Orthostatic venous pooling is common with orthostatic diastolic hypertension. This occurs in the legs while standing. Connections