To evaluate expiratory muscle endurance in middle-aged healthy subjects usi
ng incremental as well as constant expiratory loads, 14 healthy volunteers
(51 +/- 16 years) were submitted to a specific endurance test, which was pe
rformed breathing against a threshold valve, and was divided into two parts
. In part I, the load was progressively increased (50 g each 2 min) until t
ask failure occurred. The mean mouth pressure generated against the highest
load held for at least 60 sec was defined as the maximal expiratory sustai
nable pressure (Pth(max)). In part II, each subject breathed against a cons
tant submaximal expiratory load (80% Pth(max)) until task failure occurred
(expiratory endurance time or Tth(80)). Both parts of the test were repeate
d 24-48 h later. Progressive expiratory loading induced a linear increase i
n mouth expiratory pressure and the Pth(max) obtained was 141 +/- 43 cm H2O
, representing 74 +/- 28% of the maximal expiratory pressure (PEmax) Under
constant loads, the Tth(80) was 17 +/- 9 min. At the end-point of both part
s, the tension time index for expiratory muscles was dramatically increased
(>0.25), and both EMG central frequency and PEmax were decreased with no c
hanges in maximal inspiratory pressure or inspiratory capacity. Extreme dys
pnea was present in most of the subjects but no complications were observed
. The endurance of expiratory muscles can be easily assessed in healthy sub
jects using this method, which has acceptable reproducibility and tolerance
.