Respiratory Muscle Performance in Normal Elderly Subjects and Patients with COPD: Discussion


14 Oct 2014

Respiratory Muscle Performance in Normal Elderly Subjects and Patients with COPD: DiscussionThis study showed that measures of inspiratory muscle strength and endurance (as measured by the 2-min incremental loading test) were significantly less in naive COPD patients than in the normal elderly subjects matched for age, height, weight and sex distribution. The MEP, max load, Pmean and Ppk/ MIP were reproducible on repeated testing in both groups. The MIP increased on repeat visits in the normal elderly group but did not change in naive COPD subjects.
Our results for MIP in both groups are comparable to previously published data. For the normal elderly, MIP was 91 ±28 cmH20 (mean±SD), which was 102 ± 29 percent predicted (using regression equations of Black and Hyatt). The mean MIP in COPD patients was 60 ± 19 cmH20 (64 ± 18 percent predicted). This inspiratory muscle weakness was not due to malnutrition (percent ideal body weight was normal). This is very similar to other values reported for COPD patients. Only a portion of the smaller MIP in COPD patients compared with the normal elderly subjects can be attributed to RM weakness. review

Since RV was elevated (204 ±22 percent predicted, Table 1), MIP was measured at a higher absolute lung volume in COPD patients. This would result in a lower MIP even if respiratory muscle strength were normal.
Expiratory muscle strength was similar in COPD patients and the normal elderly group. The mean MEP in the normal elderly subjects was 154 ±37 cmH20 (90 ±20 percent predicted). Other investigators also have been unable to reproduce the results of Black and Hyatt for MEP in normal subjects. The mean MEP was 138 ± 65 cmH20 (76 ± 39 percent predicted) in COPD. These values are almost identical to those of Rochester and Braun but less than those of Byrd and Hyatt. Since TLC in COPD patients was 125 ±6 percent predicted, the expiratory muscles theoretically should have been at a more advantageous length for MEP generation than in normal subjects. The slightly lower mean MEP in COPD patients than in controls suggests either that the theoretic length-force advantage was apparent rather than true or that the expiratory muscles in COPD patients were in fact weaker than in the normal elderly subjects.

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