Maturational aspects of human airway smooth muscle function.

Maturational changes in the contractility and sensitivity of airway smooth muscle have been studied in an attempt to explain the increased incidence of asthma in children compared with adults. These changes are not uniform between species, however, and a clear relationship between in vitro muscle function and clinical disease does not yet exist. Over the last several years, investigators have used bronchoconstrictor challenge tests to assess airway reactivity in infants, with pulmonary functions reflecting drug effects. These tests represent changes in airway calibre, which may or may not result from differences in muscle sensitivity or contractility. Instead, the forces which oppose smooth muscle shortening, and which themselves undergo maturational change, may be responsible for the perceived heightened airway responsiveness of infants and young children. This paper reviews current knowledge regarding maturational changes in the properties of airway smooth muscle, and in the physiological forces which oppose smooth muscle shortening and airway narrowing.