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


17 Oct 2014

However, similar changes in skeletal muscle have been found with aging, disuse and malnutrition and may not be peculiar to patients with COPD. Whatever, the determinants of RM endurance are more complex than the determinants of RM strength.
For the respiratory muscles, four factors could reduce the endurance time: low basal energy stores, low rate of energy supply, reduced efficiency, and an increased external power of breathing.
The diaphragm and intercostal muscle of COPD patients have reduced energy stores, which possibly could lead to a reduction of RM endurance. Measurement of energy stores would require muscle biopsies which we did not do in this study.
Demand for energy may exceed supply in COPD patients, resulting in inspiratory muscle fatigue more quickly than in normal subjects. Energy supply may be compromised by hypoxia. The oxygen cost of breathing is higher in COPD patients compared with that in normal subjects due to reduced efficiency and increased work of breathing. read only
Therefore, although the COPD patients had only a slightly larger decrease in Sa02 than normal subjects, since the COPD patients started the test with a lower Sa02, it is possible that 02 supply to the respiratory muscles was compromised. (Oxygen supply is dependent on both blood flow and Sa02.) This could lead to reduced endurance in COPD patients but would not affect their RM strength.
The COPD patients were working at higher lung volumes (RV 204 ±22 percent predicted) compared with the normal subjects, which would contribute to reduced efficiency and adversely affect RM endurance more than RM strength.
The low energy stores, imbalance of energy supply and demand, and increased work and reduced efficiency of breathing in COPD patients explain our findings that both RM strength and endurance are decreased in COPD patients. Endurance is several times more adversely affected than strength.

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