Chest
Volume 96, Issue 1, July 1989, Pages 85-88
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The Effect of Breathing Frequency on Inspiratory Muscle Endurance During Incremental Threshold Loading

https://doi.org/10.1378/chest.96.1.85Get rights and content

We tested whether there were differences in measures of respiratory muscle endurance between tests with spontaneously chosen breathing patterns and tests with fixed breathing rates in normal volunteers. Measures of respiratory muscle endurance-maximum load tolerated, mean mouth pressure at maximum load and peak pressure at maximum load were reproducible over three tests with the spontaneously chosen breathing pattern. There was no difference in these measurements between the three tests with fixed breathing frequency. There was no difference in tidal volume, inspiratory time, and the ratio of inspiratory time to total breath duration between the tests in which breathing pattern was spontaneously chosen; there was a difference in these measurements between the tests with a fixed breathing frequency. We conclude that regulation of breathing frequency is unnecessary in the two-minute threshold loading test to obtain reproducible results for measures of respiratory muscle endurance.

(Chest 1989; 96:85-88)

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

REFERENCES (21)

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Manuscript received June 29; revision accepted October 31.

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