1817 HYPERINFLATION (AIRTRAPPING) AS A STIMULANT OF ADH RESPONSE IN CHILDREN WITH CHRONIC ASTHMA

Abstract

Elevation of plasma antidiuretic hormone (ADH) levels during status asthmaticus is well documented. The physiologic mechanisms responsible for the hormone release include hypovolemia, diminished left atrial filling due to hypoxemia and vasoconstriction from bronchospasm, stress and the role of adrenergic agents. We postulated that hyperinflation (airtrapping) in a chronic asthmatic child could reduce left atrial filling by mechanical forces and so increase the ADH response. The study included 12 chronic asthmatic children (age range:10–15 years, Sex:m:f::8:4). All bronchodilators were discontinued at least 24 hours before the study which consisted of measurement of lung functions including airway resistance and total lung capacities by body plethysmography. In addition, blood was collected for plasma ADH levels, serum and urine osmolalities. 9/12 children had 6–8 fold increase in plasma ADH levels (N-up to 1.7 mU/ml) with normal airway resistance and >120% of predicted normals for total lung capacities. 4/12 had normal lung functions with normal levels of plasma ADH levels. 4/9 children with elevated ADH levels were given furosemide to induce diuresis and this had no effect on either the plasma ADH levels nor the lung functions. In conclusion, 1. hyperinflation in itself produces ADH response 2. whether the hormone causes a negative effect on the lungs by shift in the water balance remains to be studied and 3. diuresis appears to have no effect on either the hormonal response or improving the lung functions.