Read this topic

Picture blood pooling in the legs the instant you stand up — a healthy body clamps down on those vessels and speeds the heart within seconds so the brain still gets enough pressure. Orthostatic hypotension is what you see when that clamp is too weak or too slow: pressure keeps falling past the 3-minute mark instead of recovering, and the numbers (20 systolic or 10 diastolic) are simply the line clinicians draw to call that failure abnormal.

• Orthostatic (postural) hypotension is a consensus-defined fall in blood pressure occurring on standing from lying or sitting.
• The diagnostic threshold is a systolic fall of at least 20 mmHg or a diastolic fall of at least 10 mmHg.
• This fall must be measured within 3 minutes of standing to meet the classical consensus definition.
• Normally, standing triggers baroreceptor-mediated vasoconstriction and a compensatory heart rate rise that maintains blood pressure; orthostatic hypotension reflects failure of this reflex, whether from autonomic dysfunction, volume depletion, or drug effect.
• In psychiatric practice this matters most for drugs with alpha-1 adrenergicA type of noradrenaline receptor whose blockade by some psychiatric drugs causes low blood pressure on standing.Read more → antagonism (e.g. low-potencyHow small a dose of a drug is needed to produce a given effect.Read more → and some atypical antipsychotics, tricyclic antidepressants) and for older adults, where the combination of autonomic ageing and polypharmacy raises fall and fracture risk.
• A distinct entity, initial orthostatic hypotension, causes a transient fall within 15 seconds of standing that resolves quickly and is captured by beat-to-beat monitoring rather than the standard 3-minute check.

• A 72-year-old woman starting low-dose sertraline reports light-headedness on standing.
• According to consensus criteria used in clinical practice, orthostatic (postural) hypotension is defined by a fall in blood pressure measured within how long after standing from a lying or sitting position?
• A patient is being assessed for orthostatic hypotension prior to starting an antipsychotic with high alpha-1 adrenergicA type of noradrenaline receptor whose blockade by some psychiatric drugs causes low blood pressure on standing.Read more → blocking activity.

• Classical orthostatic hypotension — fall of ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes of standing.
• Initial orthostatic hypotension — transient fall within 15 seconds of standing, recovers quickly, needs beat-to-beat (not sphygmomanometer) measurement to detect.
• Delayed orthostatic hypotension — progressive fall developing beyond 3 minutes, often assessed on prolonged tilt-table testing.
• Postural orthostatic tachycardia syndrome (POTS) — a marked heart rate rise (≥30 bpm or to >120 bpm) on standing without meeting the blood pressure fall criteria.

• Diagnosing orthostatic hypotension from symptoms (dizziness, light-headedness) alone without confirming the specific numeric blood pressure threshold.
• Using the wrong time window — checking at 10 minutes (a tilt-table protocol time point) instead of the standard 3-minute bedside check.
• Treating a pulse rise on standing as diagnostic of orthostatic hypotension, when the definition is based on the blood pressure fall, not the heart rate response.
• Forgetting the 'or' in the definition — a diastolic fall of 10 mmHg alone is sufficient even if the systolic fall is smaller than 20 mmHg.

• Identify the drug, receptor, enzyme or pharmacokinetic change named in the stem.
• Translate it into the immediate mechanism before looking at the options.
• Use timing and the adverse-effect pattern to separate the nearest alternatives.
• Check whether the question asks for mechanism, clinical consequence, monitoring or management.