  The multiplicity dependence of heavy flavour production in pp-collisions at
LHC energies is studied in the framework of the multi-pomeron exchange model.
The model is introducing the string-string interaction collectivity effects in
pp collisions, which modifies multiplicity and transverse momenta, leading to
the non-trivial mean pt vs. multiplicity (<pt>_Nch - Nch) correlation. The
string collectivity strength parameter is fixed by experimental data on
multiplicity and transverse momentum correlation in a wide energy range (from
ISR to LHC). The particles discrimination is implemented according to Schwinger
mechanism taking into account the strong decays of hadron resonances. We
demonstrate, that the faster-than-linear growth of the open charm production
with the event charged particle multiplicity, observed in experimental pp high
energy collisions, can be explained by the modification of the string tension
due to the increasing overlap and interaction of quark-gluon strings. The model
is extended for p-A interactions and the calculations for p-Pb collisions are
performed.
