Mechanical properties of the tracheal mucosal membrane in the rabbit. I. Steady-state stiffness as a function of age

Airway responsiveness is exaggerated in infancy and declines with maturatio n. These age-related differences (R.S. Tepper, T Du, A. Styhler, M. Ludwig, and J.G. Martin. Am. J. Respir. Grit. Care Med. 151: 836-840, 1995; R.S. T epper, S.J. Gunst, C.M. Doerschuk, Y. Shen, and W. Bray. J. Appl. Physiol. 78: 505-512, 1995; R.S. Tepper, J. Stevens, and H. Eigen. Am. J. Respir: CI it. Care Med. 149: 678-681, 1994) could be due to changes in the smooth mu scle, the lung, and/or the airway wall. Folding of the mucosal membrane can provide an elastic load (R.K. Lambert, J. Appl. Physiol. 71: 666-673, 1991 ), which impedes smooth muscle shortening. We hypothesized that increased s tiffness of the mucosal membrane occurs during aging, causing an increased mechanical load on airway smooth muscle and a decrease in airway responsive ness. Forty female New Zealand White rabbits between 0.75 and 35 mo of age were studied. Rectangular mucosal membrane strips oriented both longitudina lly and circumferentially to the long axis of the trachea were dissected, a nd the stress-strain relationships of each strip were tested. The results s howed that the membrane was stiffer in the longitudinal than in the circumf erential direction of the airway. However, there was no significant change with age in either orientation. We conclude that the mechanical properties of the airway mucosal membrane did not change during maturation and were no t likely to influence age-related changes in airway responsiveness.