  The presence of giant shells or loops in giant HII regions are clear witness
of the mechanical energy input from massive stars. Here we evaluate the impact
that winds may have on the structure of giant nebulae and on their supersonic
velocity dispersion. We follow the suggestion from Chu \& Kennicutt (1994) to
see if a combination of a large number of unresolved wind-driven shells caused
by massive stars could produce the integrated broad Gaussian profiles typical
of giant HII regions.
  The results, accounting for a wide range of energies, densities and velocity
or age of the expanding shells, show that supersonic Gaussian profiles may
arise only from a collection of unresolved wind-driven shells if the shells
present a peculiar velocity distribution which implies a strongly peaked age
distribution leading to an awkward star formation history. On the other hand, a
uniform distribution of ages originates profiles with a flat-topped core
defined by the terminal shell velocity and a steep decay as $v^{-6}$ up to the
largest detectable shell speed. Thus, supersonic profiles can arise only if the
final speed of the unresolved shells is supersonic. This implies an equally
supersonic random speed of motions in the ionized gas disrupting the shells
before they slow down to subsonic speeds. It also implies a mechanism,
independent of the shells caused by massive stars, responsible for the
supersonic stirring of the background medium. These facts together with the
conditions for shells to remain unresolved to present day devices (energies,
final speeds and ages), indicate that the winds may be produced by low-mass
stars. In this latter case, if the sources move supersonically in the
gravitational potential of the whole system they could stir the gas, with their
