  We study the presence of low intensity high velocity components, which we
have termed wing features in the integrated Halpha emission line profiles of
the HII region populations of the spiral barred galaxies NGC 1530, NGC 3359 and
NGC 6951. We find that more than a third of the HII region line profiles in
each galaxy show these components. The highest fraction is obtained in the
galaxy whose line profiles show the best S:N, which suggests that wing features
of this type may well exist in most, if not all, HII region line profiles.
Applying selection criteria to the wing features, we obtain a sample of HII
regions with clearly defined high velocity components in their profiles.
Deconvolution of a representative sample of the line profiles eliminates any
doubt that the wing features could possibly be due to instrumental effects. We
present an analysis of the high velocity low intensity features fitting them
with Gaussian functions; the emission measures, central velocities and velocity
dispersions for the red and blue features take similar values. We interpret the
features as signatures of expanding shells inside the HII regions. Up to a
shell radius of R(shell)~0.2R(reg), the stellar winds from the central ionizing
stars appear to satisfy the energy and momentum requirements for the formation
and driving the shell. Several examples of the most luminous HII regions show
that the shells appear to have larger radii; in these cases additional
mechanisms may well be needed to explain the kinetic energies and momenta of
the shells.
