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The Effect of Breathing Frequency on Inspiratory Muscle Endurance During Incremental Threshold Loading
Section snippets
Subjects and Techniques
Ten normal subjects volunteered for the study. Subjects had no history of respiratory illness. Spirometry was measured (FEV1 and FVC) and expressed as percent predicted using the prediction equations of Morris et al.11 The MIP and MEP were measured according to the method of Black and Hyatt12 and expressed as percent predicted using their prediction equations. The MVV was measured over 12 s and expressed as percent predicted using the prediction equations of Kory et al13 for men and Lindall et
RESULTS
Spirometry (FEV1, FVC) and tests of RM strength (MIP, MEP) and MVV are shown in Table 1. All subjects had values within normal limits. (Although the mean MEP appears low, 75.6±15.8 percent predicted, other studies have been unable to reproduce the results of Black and Hyatt12 for MEP in normal subjects.9,16)
For the three tests with an unfixed breathing frequency, there was no significant difference between tests in any of the variables tested (fb, max load, Ppk at max load, Ppk/MIP, Pmean at
DISCUSSION
This study showed that measures of inspiratory muscle endurance, as measured by the two-minute incremental threshold loading test, are not affected by breathing frequency in normal young subjects. The test gives reproducible results whether breathing frequency is spontaneously chosen or fixed at 6, 12, or 20 breaths per minute. We chose this range of fixed frequencies as our subjects' spontaneous breathing frequencies during the test ranged from 6 to 20 breaths per minute. In addition, this
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Manuscript received June 29; revision accepted October 31.