AGE-RELATED REDUCTION IN TC-99(M)-DTPA ALVEOLAR-CAPILLARY CLEARANCE IN NORMAL HUMANS

Age is known to reduce the efficacy of body organs and systems, even i n the absence of disease. The alveolar-capillary clearance (ACC) rate is representative of the alveolar-capillary barrier's functional state . We studied 29 healthy non-smokers, who were selected after clinical and radiographic evaluation. The patients were divided into three grou ps based on age: Group I, less than or equal to 30 years (n = 10); Gro up II, 31-55 years (n = 9); Group III, greater than or equal to 56 yea rs (n = 10). Each patient inhaled 750 MBq Tc-99(m)-diethylenetriamine pentaacetate (Tc-99(m)-DTPA) aerosol generated by a Venticis nebulizer (particles with a mean diameter of 1.1 mu m) for 5 min. Forty frames of 30 s duration each were acquired and the ACC rates for the right an d left lungs determined using a computer program. The mean ACC rates f or the three groups were as follows: Group I, 1.31% min(-1); Group II, 1.08% min(-1); Group III, 0.76% min(-1). The differences between Grou ps I and III (P < 0.001) and Groups II and III (P = 0.03) were shown t o be significant. There was no significant difference between Groups I and II. Possible explanations for an age-related reduction in ACC rat es include a reduction in the internal alveolar surface, the closure o f the small airways, a reduction in the lung blood capillaries and a r eduction in cardiac output. We conclude that there appears to be an ag e-related reduction in ACC rates in healthy non-smokers, even in the a bsence of clinically and radiographically detectable lung disease. How ever, larger studies are required.