  The major mass fraction of the envelope of hot luminous stars is radiatively
stable. However, the partial ionisation of hydrogen, helium and iron gives rise
to extended sub-surface convection zones in all of them. In this work, we
investigate the effect of the pressure induced by the turbulent motion in these
zones based on the mixing length theory, and search for observable
consequences. We find that the turbulent pressure fraction can amount up to ~5%
in OB supergiants, and to ~30% in cooler supergiants. The resulting structural
changes are, however, not significantly affecting the evolutionary tracks
compared to previous calculations. Instead, a comparison of macroturbulent
velocities derived from high quality spectra of OB stars with the turbulent
pressure fraction obtained in corresponding stellar models reveals a strong
correlation of these two quantities. We discuss a possible physical connection,
and conclude that turbulent pressure fluctuations may drive high-order
oscillations, which - as conjectured earlier - manifest themselves as
macroturbulence in the photospheres of hot luminous stars.
