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RBC volume deficiency in patients with excessive orthostatic decrease in cerebral blood flow velocity.

Significance statement

Orthostatic intolerance (OI) is clinically common, but is heterogeneous in the presentations and underlying causes. The authors indicated that the RBC volume deficiency plays a role in a subgroup of OI patients with excessive decreased cerebral blood flow velocity (CBFV) of middle cerebral arteries (MCA) during head-up tilt (HUT) without systemic blood pressure change by using blood volume determination with Chromium (51Cr) dilution method. Among the 25 patients enrolled, those with postural tachycardia syndrome (POTS group) had significantly more severe RBC volume deficiency than those without (Non-POTS group). This is the very first study focusing on RBC volume to discriminate the specific subgroups of patients with idiopathic OI. It not only provides a part of clues about the pathophysiology of OI, but also provokes the ideas of further studies deciphering the roles of blood volume and hemodynamic adaptation in such patients.

Figure Legend: According to the expected RBC volume derived from the body surface area of each subject, the effective RBC volume deficiency is significantly more severe in POTS (78% of expected) than that in Non-POTS (85% of expected). p=0.013.

RBC volume deficiency in patients with excessive orthostatic decrease in cerebral blood flow velocity

 

 

 

 

 

 

 

 

 

 

Journal Reference

Lin CJ1, Chu YK2, Chern CM3.

J Chin Med Assoc. 2014 Apr;77(4):174-8.

1Department of Neurology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; Department of Internal Medicine, Taipei Veterans General Hospital, Taipei, Taiwan, ROC and

2Department of Nuclear Medicine, Taipei Veterans General Hospital, Taipei, Taiwan, ROC and

3Department of Neurology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC; National Yang-Ming University School of Medicine, Taipei, Taiwan, ROC. Electronic address: [email protected]

 

Abstract

BACKGROUND:

Orthostatic intolerance (OI) is common but heterogeneous. There is a subgroup of OI patients who have excessive  decrease  in cerebral blood flow velocity (CBFV) of bilateral middle cerebral arteries (MCAs) during head-up tilt without systemic blood pressure change. This study evaluated the role of blood volume reduction in such patients.

METHODS:

Patients with idiopathic OI who had excessive orthostatic decrease (>20% of the supine level) in mean CBFV of bilateral MCAs and who also received blood volume determination were collected. The chromium (⁵¹Cr) dilution method was used for red blood cell (RBC) volume determination in these patients. The blood volume was expressed as a percentage of the expected volume. These patients were further divided into two groups, those with postural tachycardia syndrome (POTS group) and those without (non-POTS group). The data of RBC volume were compared between the two groups. Besides, we used multivariate linear regression to evaluate the factors that predict RBC volume.

RESULTS:

Twenty-five patients (13 females, median age = 28 years) were enrolled in this study. Nine of these patients had POTS (5 females, median age = 26 years) and 16 did not (8 females, median age = 29.5 years). Compared with the expected volume, the RBC volume was significantly reduced in all patients (median = 82% of the expected volume). Moreover, the RBC volume was significantly lower in the POTS group than that in the non-POTS group (78% vs. 85% of the expected volume, p = 0.013). The orthostatic decrease of MCA flow velocity was 28.3% in the POTS group and 32.5% in the non-POTS group (p = 0.140). The orthostatic pulsatility index increment was 15.4% in the POTS group and 20.5% in the non-POTS group (p = 0.438). Moreover, basic demography and hemoglobin levels were not different between the two groups. After multivariate linear regression (dependent variables including age, sex, body surface, and groups), only the presence of POTS significantly predicted the RBC volume (p = 0.006).

CONCLUSION:

The results of our study indicated that low RBC volume may play an important role in the pathophysiology of OI in this group of patients. Moreover, its role seems even more relevant in patients with POTS than in those without. Further studies for mechanistic evaluation are needed in the future.

Copyright © 2014. Published by Elsevier B.V.

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