Orthostatic Hypotension Health Article

Definition

Orthostatic hypotension refers to a reduction of blood pressure (systolic blood pressure that occurs when the heart contracts) of at lest 20 mmHg or a diastolic pressure (pressure when the heart muscle relaxes) of at least 10 mmHg within three minutes of standing.

Description

Orthostatic hypotension is a decrease of blood pressure when standing, due to changes in the blood pressure regulation systems within the body. Normally in a healthy human there is an orthostatic pooling of venous blood in the abdomen and legs when shifting positions from the supine (lying on the back) to an erect position (standing up). This redistribution of blood flow is the result of normal physiological compensatory mechanisms built into

body systems to prevent any adverse outcome (decrease in blood pressure, or hypotension) during positional change. Compensatory mechanisms include sympathetic nervous system activation and parasympathetic inhibition and increased heart rate and vascular resistance. Compensation responses restore cardiac output to vital organs and return blood pressure to normal. Orthostatic hypotension can occur if normal physiological mechanisms become faulty, such as inadequate cardiovascular compensation when shifting positions (i.e. change from supine to erect position), or due to excessive reduction in blood volume. Elderly persons seemed predisposed to orthostatic hypotension because of age-related changes; possible cardiovascular disease and the medications commonly taken by the elderly all predispose autonomic nervous system (ANS) functions. Additionally, hypertension present in 30% of persons over 75 years of age also predisposes a person to orthostatic hypotension, since hypertension reduces baroreflex sensitivity. Hypertension and the normal aging process (which typically causes blood vessel stiffness) decrease the sensitivity of specialized structures called baroreceptors, which function to maintain blood pressure, but initiating compensatory mechanisms such as increasing heart rate and vascular resistance. Persons affected with symptomatic orthostatic hypotension have symptoms when tilting head upward or when moving toward an erect position. Symptom severity varies among affected persons, but can include blurred vision, light-headedness, weakness, vertigo, tremulousness and cognitive impairment. Symptoms can be relieved within one minute of lying down. Some persons have orthostatic hypertension without symptoms.