Two types of orthostatic dysregulation assessed by diameter of inferior vena cava

Orthostatic dysregulation (OD) is common in adolescents. This study was conducted to evaluate the usefulness of the measurement of the diameter of the inferior vena cava (IVC) for objective assessment of patients with OD.

Twenty children with OD (median 14 years, range 9-15 years) and 23 age-matched healthy children (median 12 years, range 10-15 years) were enrolled. A diameter of IVC was measured by an abdominal echogram before and after a head-up tilt table testing (HUT). Changes in IVC was assessed by an arbitrary parameter, collapse index (CI) as the following equation: [(maximal IVC diameter in the supine position - maximal IVC diameter in the standing position)/(maximal IVC diameter in the supine position)]× 100. CI was evaluated 4 weeks after treatment with an adrenergic agent.

Children with OD demonstrated either higher CI or lower CI compared to that in control children: CI was more than 50 (range 50-71) in 12 patients with OD while that was equal to or less than 0 (range -225 to 0) in eight out of 20 patients. In contrast, CI was between 0 and 50 (range 1-26) in 23 healthy children. Pharmacological treatment induced the normalization in the CI in both higher and lower CI group.

OD can be classified into two subtypes: by HUT, one is characterized by an increase of IVC diameter while another is characterized by its decrease. Measurement of IVC diameter by HUT is useful to understand the pathophysiology and to assess the efficacy of treatment.