Orthostatic intolerance is a condition characterized by symptoms that develop upon standing and are typically alleviated by lying down. It represents difficulty maintaining stable blood pressure and blood flow to the brain against gravity. This inability to adapt to upright posture can manifest in various ways, from mild discomfort to severe episodes that impact daily life.
Understanding Orthostatic Intolerance
When a person moves from a lying or sitting position to standing, gravity pulls a significant amount of blood into the veins of the legs and abdomen. This pooling of blood temporarily reduces the amount of blood returning to the heart, decreasing the heart’s output and causing a transient drop in blood pressure. The body normally compensates for this shift through rapid adjustments involving the autonomic nervous system.
The autonomic nervous system, its sympathetic branch, plays a role in these adjustments. Baroreceptors, pressure sensors in the neck and chest, detect the change in blood pressure and send signals to the brain. In response, the sympathetic nervous system releases norepinephrine, which constricts blood vessels in the legs, abdomen, and pelvis, pushing blood back towards the heart and brain. This also increases heart rate. In individuals with orthostatic intolerance, these compensatory mechanisms may be inadequate, leading to sustained reductions in blood pressure, increased heart rate, or both, preventing sufficient blood flow to the brain and causing symptoms.
Common Symptoms
The symptoms of orthostatic intolerance can vary widely. Many experience lightheadedness, feeling faint or dizzy, and sometimes near-fainting or fainting upon standing. This occurs due to reduced blood flow to the brain. Visual disturbances, such as blurred vision, “white outs,” “gray outs,” or temporary blackouts, can accompany these sensations.
Another common group of symptoms involves the heart, including a rapid heart rate (tachycardia) or palpitations, which can feel like the heart is pounding, racing, or skipping beats. This rapid heart rate is the body’s attempt to compensate for the decreased blood return to the heart. Individuals may also experience fatigue and weakness, making it difficult to perform daily activities or tolerate exercise.
Cognitive difficulties, often described as “brain fog,” can manifest as trouble concentrating, memory issues, or impaired reasoning. Headaches, nausea, abdominal pain, and sweating are also frequently reported. Tremulousness or shakiness can also occur, linked to heightened sympathetic nervous system activity.
Triggers and Aggravating Factors
Several factors can worsen or trigger orthostatic intolerance symptoms. Prolonged standing is a common trigger, as it allows more time for blood to pool in the lower extremities, exacerbating circulation issues. Standing quietly or sitting upright for extended periods can also induce symptoms. Exposure to heat, such as hot weather, a warm room, or a hot bath or shower, can cause blood vessels to dilate, further contributing to blood pooling and worsening symptoms.
Dehydration is an aggravating factor, as reduced blood volume impacts the body’s ability to maintain blood pressure when upright. Illnesses, especially those causing fever or fluid loss, can temporarily worsen orthostatic intolerance. Certain medications, particularly those that lower blood pressure or affect the autonomic nervous system, can also contribute to or intensify symptoms. Large meals can divert blood flow to the digestive system, reducing blood available for circulation to the brain and worsening symptoms, a phenomenon known as postprandial hypotension.
When to Seek Medical Advice
Individuals who frequently experience symptoms of orthostatic intolerance, particularly lightheadedness, dizziness, fainting, or fatigue upon standing, should consult a healthcare professional. While occasional mild symptoms might be due to temporary factors like dehydration, persistent or severe symptoms warrant medical evaluation. Diagnosis is important to differentiate orthostatic intolerance from other conditions with similar symptoms, such as cardiac problems.
A healthcare provider will conduct a medical history review, including current medications and symptom patterns, and perform a physical examination. They may recommend tests like blood pressure monitoring in both sitting and standing positions, or a tilt table test, to observe the body’s response to upright posture. Depending on the findings, a general practitioner may refer individuals to specialists such as neurologists or cardiologists, who have expertise in conditions affecting the autonomic nervous system or heart. Seeking professional help allows for accurate diagnosis and the development of an individualized management plan.