Exercise performance in adolescents with autonomic dysfunction.

OBJECTIVE: To test the hypothesis that excessive postural tachycardia is associated with deconditioning rather than merely being an independent sign of autonomic dysfunction in patients with postural orthostatic tachycardia syndrome (POTS). STUDY DESIGN: We retrospectively analyzed records from 202 adolescents who underwent both head up-tilt and maximal exercise testing. Patients were classified as POTS if they had ≥ 30 min(-1) rise in heart rate (HR) after tilt-table test; and deconditioned if peak O(2) uptake was < 80% predicted. Changes in HR during exercise and recovery were compared between groups. RESULTS: Two-thirds of patients were deconditioned, irrespective of whether they fulfilled diagnostic criteria for POTS, but peak O(2) uptake among patients with POTS was similar to patients without POTS. HR was higher at rest and during exercise; whereas stroke volume was lower during exercise, and HR recovery was slower in patients with POTS compared with patients without POTS. CONCLUSIONS: Most patients who presented with chronic symptoms of dizziness, fatigue, or pre-syncope, were deconditioned, but, because the proportion of deconditioned patients was similar in POTS vs non-POTS groups, we conclude that HR changes in POTS are not solely because of inactivity resulting in deconditioning.

Apparent efficacy of food-based calcium supplementation in preventing rickets in Bangladesh.

To determine whether increased Ca intakes can prevent rickets in a susceptible group of children living in a rickets-endemic area of Bangladesh, we conducted a 13-month long, double-blind, clinical trial with 1-to 5-year-old children who did not present with rickets but ranked in the upper decile of plasma alkaline phosphatase (AP) activity of a screening cohort of 1,749 children. A total of 158 children were randomized to a milk-powder-based dietary supplement given daily, 6 days/week, and providing either 50, 250, or 500 mg Ca, or 500 mg Ca plus multivitamins, iron, and zinc. Upon initial screening, 194 healthy children presented with no rachitic leg signs and had serum AP in the upper decile (>260 u/dl) of the cohort. When 183 of those subjects were re-screened after a 7-month pre-trial period, 23 (12.6%) had developed rachitic leg signs, suggesting an annual risk of 21.5% in this cohort. Of those still not presenting with leg signs and completing 13 months of dietary intervention, none showed rachitic leg signs, none showed significant radiological evidence of active rickets, and all showed carpal ossification normal for age after that intervention. These results are consistent with even the lowest amount of supplemental Ca (50 mg/day) being useful in supporting normal bone development in this high-risk population.