<prompt> Orthostatic hypotension is said to be present, if systolic blood pressure falls by___while assuming standing posture from sitting posture.10 mm Hg20 mm Hg30 mm Hg40 mm Hg  <response>: Orthostatic hypotension is defined by a fall in systolic pressure 20 mmHg or in diastolic pressure 10 mmHg in response to assumption of the upright posture from a supine position within 3 min. There may also be a lack of a compensatory tachycardia, an abnormal response that suggests autonomic insufficiency, as may be seen in patients with diabetes or Parkinsons disease. Orthostatic hypotension is a common cause of postural lightheadednesssyncope and should be assessed routinely in patients for whom this diagnosis might pertain.Reference: : Harrisons medicine page no 126 