  The scattering length and effective range of the piSigma channel are studied
in order to characterize the strangeness S=-1 meson-baryon scattering and the
Lambda(1405) resonance. We examine various off-shell dependence of the
amplitude in dynamical chiral models to evaluate the threshold quantities with
the constraint at the KbarN threshold. We find that the piSigma threshold
parameters are important to the structure of the Lambda(1405) resonance and
provide further constraints on the subthreshold extrapolation of the KbarN
interaction.
