A constant-pressure molecular dynamics simulation of polymeric brushes in solvents of varying quality is presented. In contrast to previous simulations on polymer brushes, the surface osmotic pressure Pi(a) is fixed and the grafting density is allowed to vary as a function of chain length N and solvent quality. In a good solvent, the brush height h similar to N rho(a)(1/3) and Pi(a) scales as N rho(a)(x) with x = 2.5 +/- 0.2 where N is the chain length and rho(a) is the grafting density. This is in contrast with scaling theories in which x = 11/6 and self-consistent mean field theories in which x = 5/3. In a theta solvent, x = 3.0 +/- 0.2, while both theories give x = 2. For fixed Pi(a), the brush height h was found to be nearly independent of solvent quality. Results for fixed grafting sites and for annealed chains in which the tethered end of the chain is free to move within the grafting plane are presented.