Functional development of the sheep diaphragmatic ligament.

1. The diaphragmatic ligament, which lines the thoracic surface of the diaphragm, plays a major role in setting the passive compliance of the diaphragm in the adult. Since many elastic tissues are more compliant at younger ages, our aim was to determine whether this diaphragmatic ligament plays an important role during development of the diaphragm. 2. We examined the passive biaxial length-tension properties of the isolated mid-costal diaphragm from fetal, newborn and adult sheep; initially with the diaphragm intact and then with the diaphragmatic ligament removed to reveal its functional significance. 3. We found that unlike other elastic tissues the diaphragmatic ligament is stiffer in early development than in the adult. The diaphragmatic ligament supports about 75% of the passive tension in the diaphragm in the 121 day fetus (term at 147 days) declining to about 50% from 3 weeks of age. The fetal diaphragm muscle fibres are exposed to 1-7 kPa of stress over the last 26 days of gestation. 4. We suggest that the diaphragmatic ligament provides a structural framework on which the muscle fibres of the diaphragm grow in fetal life, and that the ligament's elasticity is regulated to maintain a low and constant stress on the diaphragm muscle fibres during development.