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


15 Oct 2014

The MIP increased on subsequent visits in the normal elderly subjects, primarily from visit 1 to visit 2. Since the tests were spaced one week apart and only took 30 min to complete, there should not have been a training effect. Therefore, the increase in MIP suggests a learning effect. This was seen only in the normal subjects who had no experience with any lung function testing. Although the COPD group had not undergone RM endurance testing previously, they were familiar with other pulmonary function tests. Nickerson and Keens found a 10 percent increase in MIP when 12 normal younger subjects were retested after two weeks. A third test on four subjects did not show further improvement.
The MW of the COPD group was, on average, only 37 percent of the value of the normal group (in both absolute units and percent predicted). Much of this difference could be explained by the reduced FEVA of the COPD group, since the MW is determined by the degree of airflow limitation and by respiratory muscle strength, coordination and velocity of contraction.

The measures of RM endurance (max load, Pmean and Ppk/MIP at max load) were all less in COPD patients than in the normal elderly subjects (Fig 3). However, the difference in RM endurance between the two groups was much greater than the difference in RM strength. The MIP in patients with COPD was on average 66 percent of that in the normal group, although as noted before, only part of this decrement is due to RM weakness. The MEP in patients with COPD was on average 89 percent of that in the normal group. This suggests that RM weakness is not marked in these COPD patients. Conversely, the max load and Pmean for the COPD patients were on average only 40 percent of values obtained in the normal group in the RM endurance test.
There have been previous reports of RM endurance of normal subjects. After repeated learning trials in normal subjects, Leith and Bradley found their measure of endurance, MS VC/M VY to be 80 percent.

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