  Winds from protogalactic starbursts and quasars can drive shocks that heat,
ionize, and enrich the intergalactic medium. The Sedov-Taylor solution for
point-like explosions adequately describes these blastwaves early in their
development, but as the time since the explosion ($t - t_1$) approaches the age
of the universe ($t$), cosmological effects begin to alter the blastwave's
structure and growth rate. This paper presents an analytical solution for
adiabatic blastwaves in an expanding universe, valid when the IGM is
homogeneous and contains only a small fraction of the total mass density
($\Omega_{\rm IGM} << \Omega_0$). Using this analytical solution, we examine
the role protogalactic explosions might play in determining the state of
intergalactic gas at $z \sim 2 - 4$.
