[Mechanical and metabolic reproducibility of resistance test of expiratory muscles with incremental threshold loading].
BACKGROUND
The study of respiratory muscle endurance has mainly focused on inspiratory muscles. A new method to measure expiratory muscle endurance, through incremental threshold loading using a weighted plunger valve, has recently been described.


OBJECTIVE
To evaluate the mechanical features of the plunger valve and the reproducibility of the method from the standpoint of both mechanics and metabolism.


METHODS
Four untrained healthy subjects performed an incremental test with expiratory threshold loading (50 g every 2 min) on each of three non-consecutive days; each test continued until the subject could no longer open the valve. Mouth pressure was recorded continuously during each test; on the first two test days, oxygen consumption (VO2) was also measured.


RESULTS
Opening and closing pressures were the same and were independent of expiratory flow, with a linear load-pressure relationship (4 cmH2O) for every 10 g of weight). The maximal tolerated load (MTL) in the three tests was stable for two of the subjects, whereas the maximal load was reached by the other two subjects in the second and third tests, respectively. When MTL was reached in the third test, mean and peak mouth pressures (the latter expressed as percent of maximal expiratory pressure [MEP]) were 49 +/- 4% and 71 +/- 4%, respectively; the expiratory tension-time index measured at the mouth ([PMEANmouth/MEP] x [TE/Ttot]) was 0.25 +/- 0.02 (TE: expiratory time; Ttot: total time). In the first and second tests, we also measured oxygen consumption of the recruited muscles, which were mainly the expiratory muscles (VO2respmax); consumption in the last test was 213 +/- 65 ml O2/min (2.9 +/- 1.1 ml O2/kg/min). The intraindividual coefficient of variation ranged from 6.3% to 19.5% for the mechanical parameters and from 14% to 21% for the metabolic ones.


CONCLUSIONS
The expiratory endurance test using a threshold valve allows quantification of muscle and metabolic reserve under incremental expiratory loads. The valve has appropriate mechanical characteristics for this purpose and reproducibility is acceptable, through the precise determination of the may require up to three tests.
Servei de Pneumologia, Hospital del Mar, Universitat Pompeu Fabra, Barcelona. aferrer@cspt.es
A
A
Ferrer
M
M
Orozco-Levi
J
J
Gea
R
R
Méndez
A L
AL
Ramírez
J M
JM
Broquetas
D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism; D006801:Humans; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011312:Pressure; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D012132:Respiratory Muscles / Q000378:metabolism* / Q000502:physiology*
D002245:Carbon Dioxide; D010100:Oxygen