Update on the theory and management of orthostatic intolerance and related syndromes in adolescents and children

Abstract

Orthostasis means standing upright. One speaks of orthostatic intolerance (OI) when signs, such as hypotension, and symptoms, such as lightheadedness, occur when upright and are relieved by recumbence. The experience of transient mild OI is part of daily life. 'Initial orthostatic hypotension' on rapid standing is a normal form of OI. However, other people experience OI that seriously interferes with quality of life. These include episodic acute OI, in the form of postural vasovagal syncope, and chronic OI, in the form of postural tachycardia syndrome. Less common is neurogenic orthostatic hypotension, which is an aspect of autonomic failure. Normal orthostatic physiology and potential mechanisms for OI are discussed, including forms of sympathetic hypofunction, forms of sympathetic hyperfunction and OI that results from regional blood volume redistribution. General and specific treatment options are proposed.

Figure 1. Arterial pressure (upper panels) and cerebral blood flow velocity measured by transcranial Doppler ultrasound (lower panels)

The left panels show data from a vasovagal syncope patient, while the right panels show data from a POTS patient. Arterial pressure and CBFv are initially stable, then decrease gradually and finally abruptly decrease by >50% with loss of consciousness in the syncope patient. The POTS patient has no decrease in arterial pressure, but has a >20% reduction in CBF throughout tilt. CBFv: Cerebral blood flow velocity; POTS: Postural tachycardia syndrome.

Figure 2. Image showing initial orthostatic hypotension

Arterial blood pressure is shown during a standing test. The blood pressure begins to decrease immediately upon standing, reaching its nadir in about 15 s and recovers spontaneously. The interbeat interval is quite decreased when hypotensive, corresponding to an increased heart rate.

Figure 3. Hemodynamic and neurovascular changes during upright tilt in a representative healthy volunteer

The left panel shows from top to bottom: arterial pressure, MSNA from the peroneal nerve, HR and cardiac output. The right panel shows from top to bottom: TPR, CBFv by transcranial Doppler ultrasound, stroke volume and a vagal index calculated from the respiratory sinus arrhythmia component of the frequency spectrum of HR variability. The subject is a representative healthy volunteer. During upright tilt, systolic, diastolic and MAPs increase slightly, while pulse pressure is decreased with a decrease in stroke volume by approximately 40%. HR increases so that cardiac output is only decreased by 20% because of the increase in HR. Cerebral blood flow decreases by 5–10%. Both total peripheral vascular resistance and muscle sympathetic nerve activity increase, while the vagal index decreases, reflecting, respectively, sympathetic activation and parasympathetic withdrawal. CBFv: Cerebral blood flow velocity; HR: Heart rate; MAP: Mean arterial pressure; MSNA: Muscle sympathetic nerve activity; TPR: Total peripheral vascular resistance.

Figure 4. Neurogenic orthostatic hypotension

Arterial blood pressure in the upper panel declines steadily during upright stance, while heart rate is only slightly increased.

Figure 5. Diagram showing representative heart rate in the upper panel and mean arterial pressure in the lower panel during upright tilt in a postural tachycardia syndrome patient

Heart rate increases, while MAP is stable throughout tilt in postural tachycardia syndrome. MAP: Mean arterial pressure.

Figure 6. Representative heart rate in the upper panel and mean arterial pressure in the lower panel during upright tilt for a postural syncope patient

Changes during tilt occur over three stages: during the first stage, following initial hypotension, MAP stabilizes at a slightly higher than resting pressure while heart rate increases. During the second stage, MAP begins to fall gradually, while heart rate continues to increase. Note that the increment in heart rate from supine to upright fulfills tachycardia criteria for postural tachycardia syndrome. During the third stage, MAP and then heart rate fall abruptly and rapidly as loss of consciousness supervenes. BP: Blood pressure; MAP: Mean arterial pressure.

Figure 7. An asystolic faint

This is episodic, relatively infrequent and unrelated to intrinsic sinus node disease. Asystolic faints are associated with opisthotonic posturing and have been sometimes referred to as ‘convulsive syncope’. BP: Blood pressure.