Common syndromes of orthostatic intolerance

Abstract

The autonomic nervous system, adequate blood volume, and intact skeletal and respiratory muscle pumps are essential components for rapid cardiovascular adjustments to upright posture (orthostasis). Patients lacking sufficient blood volume or having defective sympathetic adrenergic vasoconstriction develop orthostatic hypotension (OH), prohibiting effective upright activities. OH is one form of orthostatic intolerance (OI) defined by signs, such as hypotension, and symptoms, such as lightheadedness, that occur when upright and are relieved by recumbence. Mild OI is commonly experienced during intercurrent illnesses and when standing up rapidly. The latter is denoted "initial OH" and represents a normal cardiovascular adjustment to the blood volume shifts during standing. Some people experience episodic acute OI, such as postural vasovagal syncope (fainting), or chronic OI, such as postural tachycardia syndrome, which can significantly reduce quality of life. The lifetime incidence of ≥1 fainting episodes is ∼40%. For the most part, these episodes are benign and self-limited, although frequent syncope episodes can be debilitating, and injury may occur from sudden falls. In this article, mechanisms for OI having components of adrenergic hypofunction, adrenergic hyperfunction, hyperpnea, and regional blood volume redistribution are discussed. Therapeutic strategies to cope with OI are proposed.

Keywords: autonomic nervous system; hypocapnia; orthostatic hypotension; postural tachycardia syndrome; syncope.

FIGURE 1

IOH upon standing. There is a short-lived decrease in BP (upper panel) and increase in HR (lower panel). The fall in BP is resolved within ∼20 seconds. The patient experienced transient lightheadedness.

FIGURE 2

Decreased CBFv measured by transcranial Doppler ultrasound occurs during a VVS, (shown in the upper panel) and in POTS (shown in the bottom panel). During VVS, CBF declines gradually at first and then more abruptly as the patient acutely loses consciousness. In POTS, CBF is fairly uniformly reduced; there is no loss of consciousness, although lightheadedness is typical.

FIGURE 3

NOH: mean arterial pressure (MAP, top panel) and HR ( bottom panel) are shown during a standing test. The BP begins to decrease immediately upon standing and continues to decrease until the patient is supine. HR increases by only a small amount despite hypotension.

FIGURE 4

A representative POTS patient’s data. HR (top panel) increases excessively without significant change in mean arterial pressure (MAP, bottom panel) change during a tilt test.

FIGURE 5

A representative VVS patient’s data during a tilt test. HR (top panel) increases until late into the course when it falls abruptly. Mean arterial pressure (MAP, bottom panel) initially stabilizes, then slowly decreases, and finally falls abruptly along with HR. SNA, sympathetic nervous activity; TPR, total peripheral resistance.

FIGURE 6

Asystolic postural VVS during a tilt test. HR (electrocardiogram, top panel) rapidly transits to asystole from a preceding sinus tachycardia. BP (bottom panel) falls in concert. There was no prodrome, although careful scrutiny shows a small decrease in BP before asystole supervenes.