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J Appl Physiol 89: 2007-2014, 2000;
8750-7587/00 $5.00
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Vol. 89, Issue 5, 2007-2014, November 2000

Effect of expiratory resistive loading on the noninvasive tension-time index in COPD

William H. Thompson, Paula Carvalho, James P. Souza, and Nirmal B. Charan

Pulmonary Research Laboratory, Veterans Affairs Medical Center, Boise, Idaho 83702; and Division of Pulmonary/Critical Care Medicine, Department of Medicine, University of Washington, Seattle, Washington 98195

Expiratory resistive loading (ERL) is used by chronic obstructive pulmonary disease (COPD) patients to improve respiratory function. We, therefore, used a noninvasive tension-time index of the inspiratory muscles (TTmus = <A><AC>P</AC><AC>&cjs1171;</AC></A>I/PImax × TI/TT, where <A><AC>P</AC><AC>&cjs1171;</AC></A>I is mean inspiratory pressure estimated from the mouth occlusion pressure, PImax is maximal inspiratory pressure, TI is inspiratory time, and TT is total respiratory cycle time) to better define the effect of ERL on COPD patients. To accomplish this, we measured airway pressures, mouth occlusion pressure, respiratory cycle flow rates, and functional residual capacity (FRC) in 14 COPD patients and 10 normal subjects with and without the application of ERL. TTmus was then calculated and found to drop in both COPD and normal subjects (P < 0.05). The decline in TTmus in both groups resulted solely from a prolongation of expiratory time with ERL (P < 0.001 for COPD, P < 0.05 for normal subjects). In contrast to the COPD patients, normal subjects had an elevation in <A><AC>P</AC><AC>&cjs1171;</AC></A>I and FRC, thus minimizing the decline in TTmus. In conclusion, ERL reduces the potential for inspiratory muscle fatigue in COPD by reducing TI/TT without affecting FRC and <A><AC>P</AC><AC>&cjs1171;</AC></A>I.

chronic obstructive pulmonary disease; fatigue; mouth occlusion pressure


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