Interrelationships between obesity, obstructive sleep apnea syndrome and cardiovascular risk in obese adolescents

Background/Objectives

Obstructive sleep apnea syndrome (OSAS) may be a cardiovascular disease (CVD) risk factor independently of obesity in adults. Pediatric studies have associated OSAS with endothelial dysfunction, but few studies have examined relationships between OSAS and macrovascular sequelae. Our objective was to examine OSAS’s independent contribution to macrovascular CVD risk measures in obese adolescents.

Subjects/Methods

This cross-sectional observational study was conducted at Children’s Hospital of Philadelphia Clinical Research and Academic Sleep Centers, and University of Pennsylvania Vascular Research Unit. 31 obese non-diabetic adolescents underwent anthropometric measurements, overnight polysomnography, fasting laboratory draw, and cardiovascular imaging. Cardiovascular outcome measures included maximal carotid intima-media thickness (cIMTmax), a measure of carotid structural changes, and carotid-femoral pulse wave velocity (CFPWV), an aortic stiffness measure whose relationship vis-à-vis OSAS in children has not been previously examined. Carotid diameter and augmentation index (AIx, measuring central pressure augmentation from wave reflections) were assessed. Potential confounding variables examined included blood pressure, lipoproteins, high-sensitivity C-reactive protein, insulin and glucose.

Results

The apnea hypopnea index, a primary OSAS measure, was not associated with cIMTmax, carotid diameter, CFPWV or AIx. BMI associated positively with cIMTmax (r=0.52, p=0.006) and CFPWV (r=0.45, p=0.01). Mean asleep end-tidal CO₂ was negatively associated with carotid diameter (r=−0.63, p<0.0005). Insulin levels were negatively associated with AIx (r=−0.53, p=0.02).

Conclusions

OSAS did not predict carotid structural changes or arterial stiffness independently of BMI in obese adolescents. Higher insulin levels associated with lower central pressure wave augmentation. Finally, long-term hypercapnia may predispose to carotid narrowing.

Hyponatremia and polyuria in children with central diabetes insipidus: challenges in diagnosis and management

Five patients with well-controlled, long-standing, central diabetes insipidus had acute development of dehydration, hyponatremia, and inappropriate natriuresis in the setting of polyuria resistant to exogenous antidiuretic hormone. Hyponatremia and dehydration worsened with fluid restriction or use of exogenous antidiuretic hormone. We discuss the challenges in diagnosis and management of probable salt wasting in children with central diabetes insipidus.

Insulin-like growth factor binding protein-1 levels in the diagnosis of hypoglycemia caused by hyperinsulinism

The diagnosis of hypoglycemia caused by hyperinsulinism may be difficult because insulin levels are not uniformly elevated at the time of hypoglycemia. Insulin-like growth factor binding protein-1 (IGFBP-1) is a 28 kd protein whose secretion is acutely inhibited by insulin. We hypothesized that serum levels of IGFBP-1 would be a useful marker of hyperinsulinism. We measured IGFBP-1 levels during the course of standardized fasting studies in hospitalized children; 36 patients became hypoglycemic during the fasting studies, and samples obtained at the point of hypoglycemia were analyzed. On the basis of the currently used diagnostic criteria, 13 children had hyperinsulinism, 16 had ketotic hypoglycemia or no disorder, 3 had hypopituitarism or isolated growth hormone deficiency, 2 had glycogen storage disease type 1 and 2 had fatty acid oxidation disorders. In control subjects (children with ketotic hypoglycemia or no disorder), IGFBP-1 levels rose during fasting to a mean of 343.8 +/- 71.3 ng/ml in the sample drawn at the time of hypoglycemia. Mean IGFBP-1 levels at hypoglycemia for the entire group with hyperinsulinism were 52.4 +/- 11.5 ng/ml, significantly different from levels seen in control subjects (p < 0.0001). In children with moderately controlled hyperinsulinism (fasting tolerance > 4 hours), mean IGFBP-1 levels at the time of hypoglycemia were 71.5 +/- 16.9 ng/ml. IGFBP-1 levels in the children with poorly controlled hyperinsulinism (fasting tolerance < 4 hours) failed to rise during fasting, with a mean of 30.1 +/- 10.4 ng/ml in the final sample. IGFBP-1 levels were inversely correlated with serum insulin and C-peptide levels (r = -0.71 and -0.72, respectively; p < 0.0001). Patients with other endocrinologic or metabolic diseases that result in fasting hypoglycemia demonstrated a rise in IGFBP-1 levels similar to that seen in ketotic hypoglycemia. Low serum levels of IGFBP-1 at the time of hypoglycemia provide an additional marker of insulin action that might help to differentiate hyperinsulinism from other hypoglycemic disorders.