Regional lung function in children: the accuracy of nitrogen-13 inhalation and infusion studies

The assumptions made in 13N lung function tests in children with pulmonary or cardiac disorders have been examined. The index of lung function employed was the height/area (H/A) of the lung curves obtained following either bolus inhalation or infusion of 13N. Three aspects were considered: (1) the accuracy of H/A values with count rates obtained in typical patients; (2) the effect on perfusion H/A values of prolonged arrival of isotope in the lungs; and (3) the effect on perfusion H/A values of recirculation of isotope through the lungs due to a right-to-left intracardiac shunt. It was found that, for inhalation studies, the index H/A was sufficiently accurate to distinguish localised from generalised disease. For perfusion studies, prolonged arrival of isotope in the lungs caused a reduction in measured H/A values of up to 15%. In the presence of a right-to-left shunt recirculation of isotope could prevent the detection of a small, poorly-ventilated lung component. It is concluded that the use of 13N for measurement of ventilation/perfusion balance is not a sensitive method for monitoring the progress of generalised pulmonary disease.