Comparison of incremental and constant load tests of inspiratory muscle endurance in COPD

¹ Depts of Pulmonary Physiology and; Physiotherapy, Sir Charles Gairdner Hospital, Nedlands WA 6009; and School of Physiotherapy, Curtin University of Australia, Bentley WA, 6102
² Physiotherapy, Sir Charles Gairdner Hospital, Nedlands WA 6009; School of Physiotherapy, Curtin University of Australia, Bentley WA, 6102; and Lung Institute of Western Australia
³ Depts of Pulmonary Physiology and
⁴ Depts of Pulmonary Physiology and; School of Physiotherapy, Curtin University of Australia, Bentley WA, 6102; and School of Anatomy and Human Biology, University of Western Australia, Nedlands WA 6009, Australia

^* To whom correspondence should be addressed. E-mail: peter.eastwood{at}health.wa.gov.au.

	Abstract

To determine the relative value of incremental and constant load tests in detecting changes in inspiratory muscle endurance following high-intensity inspiratory muscle training (H-IMT) in chronic obstructive pulmonary disease (COPD).

16 subjects (11 males, FEV₁ 37.4±12.5%) underwent H-IMT. 17 subjects (11 males, FEV₁ 36.5±11.5%) underwent sham inspiratory muscle training (S-IMT). Training took place 3 times a week for 8 weeks. Baseline and post-training measurements were obtained of maximum threshold pressure sustained during an incremental load test (Pthmax) and time breathing against a constant load (Tlim). Breathing pattern was unconstrained.

H-IMT increased Pthmax and Tlim relative to baseline and to any change seen following S-IMT. The effect size for Pthmax was greater than for Tlim. Post-training tests were accompanied by changes in breathing pattern, including decreased duty cycle, which may have served to decrease inspiratory work and thereby contribute to the increase in Pthmax and Tlim in both groups.

When assessing inspiratory muscle function in COPD using tests in which the pattern of breathing is unconstrained, we recommend incremental load tests be used in preference to constant load tests. However, to attribute changes in these tests to improvements in inspiratory muscle endurance, breathing pattern should be controlled.