Rheumatoid arthritis (RA) is a rheumatic disease
that  primarily  affects  peripheral  joints,  but  its  mortality  is
directly related  to pulmonary  involvement. Some results have
shown  that  spirometric  exams  are  often  normal  in  these
individuals.  Recently,  a  prototype  of  an  instrument
implementing  the  Forced  Oscillation  Technique  (FOT)  was
used  in  the  analysis  of  these  patients,  showing  significant
adverse  modifications  in  biomechanics.  This  study  evaluates
the effect of the duration of the disease on respiratory function
by  spirometry and FOT. For  this purpose,  the  study  involved
11  normal  subjects  and  38  patients  that  were  classified  into
four  groups  according  to  disease  duration.  There  was  no
change  in  the  values  of  spirometric  parameters  with  disease
duration. On the other hand, the FOT resistive parameters R0
and  Rm  increased  significantly  (p<0.0001,  p<0.00001),  while
the  dynamic  compliance  (Cdyn,rs)  decreased  significantly
(p<0.00001), with   disease duration. The  correlations  confirm
these  results, demonstrating r2
 values of 0.11  for R0 and 0.24
for Cdyn,rs. We conclude that there are significant changes in
the  biomechanical  properties  of  the  respiratory  system  of
individuals with RA that are associated with disease duration
and that this early changes may be detected by the FOT.