Initial orthostatic hypotension: review of a forgotten condition

Abstract

Several studies have shown that standing up is a frequent (3-10%) trigger of loss of consciousness both in young and old subjects. An exaggerated transient BP (blood pressure) fall upon standing is the underlying cause. IOH (initial orthostatic hypotension) is defined as a transient BP decrease within 15 s after standing, >40 mmHg SBP (systolic BP) and/or >20 mmHg DBP (diastolic BP) with symptoms of cerebral hypoperfusion. It differs distinctly from typical orthostatic hypotension (i.e. BP decrease >20 mmHg SBP and/or >10 mmHg DBP after 3 min of standing) as the BP decrease is transient. Only continuous beat-to-beat BP measurement during an active standing-up manoeuvre can document this condition. As IOH is only associated with active rising, passive tilting is of no diagnostic value. The pathophysiology of IOH is thought to be a temporal mismatch between cardiac output and vascular resistance. The marked decrease of vascular resistance during rising is similar to that observed at the onset of leg exercise and is absent during head-up tilting. It is attributed to vasodilatation in the working muscle through local mechanisms. Standing up causes an initial increase in venous return through the effects of contraction of leg and abdominal muscles. The consequent sudden increase in right atrial pressure may contribute to the fall in systemic vascular resistance through a reflex effect. This review alerts clinicians and clinician scientists to a common, yet often neglected, condition that occurs only upon an active change of posture and discusses its epidemiology, pathophysiology and management.

Postural Hyperventilation as a Cause of Postural Tachycardia Syndrome: Increased Systemic Vascular Resistance and Decreased Cardiac Output When Upright in All Postural Tachycardia Syndrome Variants

“…Changing from supine to standing transfers >500 mL of CBV caudally, transiently decreasing CBV and increasing blood within the splanchnic vasculature and lower extremities 18, 28, 50. There is a period of IOH28 during which BP, CO, and CBF transiently decrease because of the time lag in the onset of sympathetic compensation.…”

“…There is a period of IOH28 during which BP, CO, and CBF transiently decrease because of the time lag in the onset of sympathetic compensation. BP reaches its nadir 10 to 20 seconds after standing 51.…”

“…This allowed for the manipulation of the end‐tidal concentration of one gas while maintaining the end‐tidal concentration of the other gases constant. Eucapnia was restored using 21% O 2 balanced with N 2 while maintaining CO 2 near 40 Torr by adding CO 2 to the breathing circuit as needed, as we have previously described 28. The patients maintained spontaneous breathing frequency and TV throughout.…”

“…The first minute of tilt after a prolonged supine rest often includes a period of hemodynamic instability known as “initial orthostatic hypotension” (IOH),28 caused by the translocation of blood from the upper body to the lower body while a lag in compensatory adrenergic vasoconstriction allows a decrease in CBV and BP and a concomitant increase in HR. For that reason, the first minute of tilt is often not used for analysis.…”

Clinical classification of orthostatic hypotensions

“…Initial orthostatic hypotension (iOH) is defined as a transient BP decrease of[40 mmHg systolic or[20 mmHg diastolic with symptoms of cerebral hypoperfusion within 5-15 s after standing, usually resolving by 20 s [5,6]. This phenomenon, which is common in healthy adolescents and may represent an underrecognized cause of orthostatic syncope in the elderly, is more pronounced during active standing than passive tilting [3].…”