Symposium on Blood Volume in Clinical Medicine
Blood Volume Perturbations in the Postural Tachycardia Syndrome

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ABSTRACT

The postural tachycardia syndrome (POTS) is characterized by excessive orthostatic tachycardia with chronic symptoms that are associated with upright posture. These chronic symptoms (of at least 6 months’ duration) include tachycardia, exercise intolerance, lightheadedness, extreme fatigue, headache, and mental clouding. Patients with POTS demonstrate an increase in heart rate of at least 30 beats/min within 5 to 30 minutes of assuming an upright posture, in the absence of orthostatic hypotension (a fall in blood pressure > 20/10 mm Hg) and in the absence of other medical disorders that might cause tachycardia. POTS can be associated with a high degree of functional disability. The blood volume has been found to be low in many patients with POTS. This article will review some of the data regarding blood volume perturbations in POTS, blood volume regulation in POTS, and potential treatment approaches.

Section snippets

Hypovolemia in the Postural Tachycardia Syndrome

Clinical research studies of patients with POTS have found patients with POTS to have low plasma volumes,12., 13. a low red cell volume,14., 15. or both.3

Fouad et al13 described a group of 11 patients with orthostatic intolerance in whom they found a marked reduction in blood volume without an obvious underlying cause. They labeled this phenomenon as “idiopathic hypovolemia.” These patients had a significant reduction in total blood volume (73% of the normal values for that laboratory) and

Blood Volume Regulation in the Postural Tachycardia Syndrome

The renin-angiotensin-aldosterone system plays a key role in the hormonal regulation of plasma volume in humans. Plasma renin activity (PRA) and angiotensin II should increase in response to hypovolemia to promote a corrective increase in blood volume.

Patients with orthostatic tachycardia who were also hypovolemic had low levels of standing PRA12 compared with normovolemic patients and control subjects. In a more recent study, the aldosterone level was lower in the patients with POTS in both

Treatment of Hypovolemia in the Postural Tachycardia Syndrome

Although hypovolemia in patients with POTS may be important for an understanding of the pathophysiology, there are scant data on the treatment of this problem once it has been discovered. In patients with a deficit in plasma volume, acute blood volume administration (or increase) has been shown to diminish the orthostatic tachycardia and improve symptoms. This has been shown using both intravenous albumin (50 mg per day × 3 days)13 and 1 liter of normal saline solution.21 On a chronic basis, we

Summary

Hypovolemia is a common finding in the postural tachycardia syndrome and may play an important underlying role in its pathophysiology. Abnormalities of both plasma volume and red cell volume have been noted. Further research is required to understand the exact nature of the blood volume dysregulation and to determine optimal treatment strategies.

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    Citation Excerpt :

    The hemodynamic properties of POTS identify closely with those seen in moderate hemorrhage in that central hypovolemia, reduced cardiac output, and increased adrenergic-mediated vasoconstriction occur (Fu et al., 2010; Stewart, 2012), while BP is maintained and may even increase (orthostatic hypertension) (Grubb et al., 1997). Reduced systemic venous return and reduced cardiac output contribute to reduced central blood volume when upright,(Barcroft et al., 1944) and absolute hypovolemia can be found (Fouad et al., 1986; Raj and Robertson, 2007; Raj et al., 2005) similar to bed-rested patients or astronauts with gravitational deconditioning (Montgomery et al., 1993). In others, redistributive central hypovolemia when upright occurs due to decreased lower extremity venous tone (Stewart and Montgomery, 2004), or splanchnic pooling (Stewart et al., 2006a).

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