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


16 Oct 2014

Respiratory Muscle Performance in Normal Elderly Subjects and Patients with COPD: OutcomeIn the endurance test of Nickerson and Keens, mean SIP/MIP percent was 68 ±3 percent. Our normal elderly subjects had a Ppk/MIP of 79 ±19 percent which was similar to the SIP max/MIP of 77 ± 6 percent found in normal younger subjects by Martyn et al. This suggests that learning occurs during the first 2-min incremental test with no significant change in results on repeated visits. In our patients with COPD, mean Ppk/MIP was 48 ± 16 percent (61 percent of the mean Ppk/MIP of the normal elderly group). read more

However, Belman and Mittman found MSVC/MW in ten COPD patients prior to training to be 79 ± 22 percent. This is very similar to the value noted before for normal subjects by Leith and Bradley. The MW for our COPD patients was very similar to that of Belman and Mittman (46 ± 18 L/min vs 43 ± 22 L/min), which suggests that the two groups of patients were similar. The lower value of Ppk/MIP in our COPD patients compared with the MSVC/MW in Belman and Mitt-mans patients suggests that these two ratios are measuring different aspects of endurance. Therefore, different tests of endurance may measure different features of the respiratory system and may not be directly comparable. The lower level for Ppk/MIP compared with MSVC/MVV suggests that the inspiratory muscles may fatigue more quickly when generating pressure against a load compared with sustaining ventilation with unloaded breathing.
There are several reasons why RM endurance could be relatively more compromised than RM strength in COPD patients compared with normal elderly subjects. The measurement of strength involves a maximum static contraction of RM fibers. There is controversy as to whether diaphragmatic muscle mass is increased, decreased or unaffected in COPD. There have been reports of muscle fiber atrophy in both the diaphragm and intercostal muscles of patients with COPD. Atrophy would decrease strength.

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