FIGURE 4.

Both (A) mean aortic pressure and (B) midwall stress were lower in fetal or newborn lambs than in adult sheep. (C) The elastic modulus was lower in fetal and newborn lambs, compared with adult sheep at baseline levels of aortic pressure, but surprisingly, the reverse was observed when the elastic modulus was compared at equal levels of aortic stress in fetal and newborn lambs and adult sheep (D) or when compared at the fetal/newborn levels of aortic stress (E). Moreover, values were similar in fetal and newborn lambs suggesting that increases in aortic stiffness occur well after birth. *p < 0.05 (replot from Pagani et al., 1979).