Flow-mediated vasodilation and endothelium function in children with postural orthostatic tachycardia syndrome.

The study was designed to explore flow-mediated vasodilation (FMD) and endothelium function in children with postural orthostatic tachycardia syndrome (POTS). The patient group consisted of 46 children 12 +/- 3 years of age who were diagnosed with POTS from June 2008 to January 2009 by head-up test or head-up tilt test at Peking University First Hospital. Twenty healthy children 12 +/- 4 years of age were selected for the control group. Plasma concentrations of nitric oxide (NO) and activity of NO synthase (NOS) were determined in the patient and control groups. FMD of each participant's brachial artery was measured using color Doppler vascular ultrasound and a comparison of FMDs and plasma NO and NOS activities between the 2 groups was done using independent t test. No significant differences were found between the POTS and control groups in age, sex ratio, height, body weight, baseline blood pressure, heart rate, and baseline brachial artery diameter. Patients in the POTS group had larger FMD (10.8 +/- 4.4%) than children in the control group (5.7 +/- 2.2%), and this difference was significant (p <0.01). Plasma NO and NOS levels were significantly higher in the POTS group than in the control group (NO 74 +/- 19 micromol/L in POTS group vs 62 +/- 6 micromol/L in control group, p <0.01; NOS 21 +/- 3 U/mL in POTS group vs 15 +/- 1 U/mL in control group, p <0.01). In addition, there was a significant correlation between FMD and the NOS activity. In conclusion, augmented FMD and abnormal function of vascular endothelium may play an important role in POTS in children.