  The aim of this work is to address the description of hyperinflation regimes
in economy. The spirals of hyperinflation developed in Brazil, Israel, and
Nicaragua are revisited. This new analysis of data indicates that the episodes
occurred in Brazil and Nicaragua can be understood within the frame of the
model available in the literature, which is based on a nonlinear feedback (NLF)
characterized by an exponent $\beta>0$. In the NLF model the accumulated
consumer price index carries a finite time singularity of the type
$1/(t_c-t)^{(1- \beta)/\beta}$ determining a critical time $t_c$ at which the
economy would crash. It is shown that in the case of Brazil the entire episode
cannot be described with a unique set of parameters because the time series was
strongly affected by a change of policy. This fact gives support to the "so
called" Lucas critique, who stated that model's parameters usually change once
policy changes. On the other hand, such a model is not able to provide any
$t_c$ in the case of the weaker hyperinflation occurred in Israel. It is shown
that in this case the fit of data yields $\beta \to 0$. This limit leads to the
linear feedback formulation which does not predict any $t_c$. An extension for
the NLF model is suggested.
