  [Abridged] Due to their large distances, high-z galaxies are observed at a
very low spatial resolution. In order to disentangle the evolution of galaxy
kinematics from low resolution effects, we have used Fabry-Perot 3D Ha
data-cubes of 153 nearby isolated galaxies from the GHASP survey to simulate
data-cubes of galaxies at z=1.7. We show that the inner velocity gradient is
lowered and is responsible for a peak in the velocity dispersion map.
Toy-models of rotating disks have been built to recover the parameters from low
resolution data. The poor resolution makes the kinematical inclination
uncertain and the center difficult to recover. The major axis is retrieved with
an accuracy higher than 5deg for 70% of the sample. Toy-models also enable to
retrieve statistically the maximum velocity and the mean velocity dispersion of
galaxies with a satisfying accuracy. This validates the use of the Tully-Fisher
relation for high-z galaxies but the loss of resolution induces a lower slope
at high-z. We conclude that the main kinematic parameters are better
constrained for galaxies with an optical radius larger than three times the
seeing. The simulated data have been compared to actual high-z galaxies data in
the redshift range 3>z>0.4. For rotation-dominated galaxies, we find that the
use of the velocity dispersion central peak as a signature of rotating disks
may misclassify slow and solid body rotators (~30% of our sample). We show that
the projected data cannot reproduce the high velocity dispersion observed in
high-z galaxies except when no beam smearing correction is applied. This
unambiguously means that, at the opposite of local evolved galaxies, there
exists at high redshift at least a population of disk galaxies for which a
large fraction of the dynamical support is due to random motions.
