  Inelastic neutron scattering data for YBaCuO as well as for LaSrCuO indicate
incommensurate neutron scattering peaks with incommensuration $\delta(x)$ away
from the $(\pi,\pi)$ point. $T_c(x)$ can be replotted as a linear function of
the incommensuration for these materials. This linear relation implies that the
constant that relates these two quantities, one being the incommensuration
(momentum) and another being $T_c(x)$ (energy), has the dimension of velocity
we denote $v^*$: $k_B T_c(x) = \hbar v^* \delta(x)$. We argue that this
experimentally derived relation can be obtained in a simple model of Josephson
coupled stripes. Within this framework we address the role of the $O^{16} \to
O^{18}$ isotope effect on the $T_c(x)$. We assume that the incommensuration is
set by the {\em doping} of the sample and is not sensitive to the oxygen
isotope given the fixed doping. We find therefore that the only parameter that
can change with O isotope substitution in the relation $T_c(x) \sim \delta(x)$
is the velocity $v^*$. We predict an oxygen isotope effect on $v^*$ and expect
it to be $\simeq 5%$.
