Measurement of inspiratory muscle performance with incremental threshold loading: a comparison of two techniques

Sustainable inspiratory pressure and incremental threshold loading for respiratory muscle endurance in chronic obstructive pulmonary disease: A pilot study

INTRODUCTION

A prolonged mismatch between the demand for respiratory muscle work and the capacity to meet that demand in chronic obstructive pulmonary disease (COPD) can result in symptoms of dyspnea and the development of muscle fatigue.

OBJECTIVES

The purpose of this study was to compare two different respiratory muscle endurance assessment methods of sustainable inspiratory pressure (SIP) and incremental threshold loading (ITL) in COPD.

METHODS

Thirty-four patients diagnosed with COPD were included in the study. Physical and demographic characteristics of the subjects were recorded. Pulmonary function testing (PFT), modified Medical Research Council (MMRC) dyspnea scale, COPD assessment test, inspiratory and expiratory muscle strength (MIP and MEP, respectively) measurement and six-minute walk test (6MWT) were used to assess subjects. Two different respiratory muscle endurance tests (SIP and ITL) were performed within 48 hours apart, and each test was repeated two times on the same day.

RESULTS

There was no correlation between the SIP and ITL tests (r = 0.069, P = .699). According to the test-retest reliability analysis, both tests were reproducible (ICC = 0.843; P < .001 for SIP, ICC = 0.905; P < .001 for ITL). Finding no differences between repeated tests showed that tests are not affected by learning effect.

CONCLUSION

The SIP and ITL tests are used for the same purpose but have different characteristics. Regarding the relationship between the other parameters and tests, the ITL is well tolerated and reflects the differences in respiratory muscle endurance better.

Reproducibility of inspiratory muscle endurance testing using PowerBreathe for COPD patients

BACKGROUND

Assessing the strength and endurance of respiratory muscles is fundamental for characterizing respiratory muscle dysfunction. Although a variety of tests are used to evaluate respiratory muscle endurance, not all of them are applicable in clinical practice. Assessments can be made using a practical device called PowerBreathe®, but its reproducibility has not been tested in chronic obstructive pulmonary disease (COPD) patients.

AIM

To verify the reproducibility of the inspiratory muscle endurance test using a manometer and PowerBreathe® in COPD patients.

METHODS

A cross-sectional study was used. In total, 19 moderate-severe COPD patients, male and female, aged 50 to 80 years took part in the research. This evaluation consisted of 2 tests: an incremental test and a constant one held on the same day and repeated after 48 hr. The incremental test started with 10-cm H₂ O, adding 10-cm H₂ O every 2 min and taking 1 min of rest before increasing the load. The highest load that could be sustained for at least 1 min was considered the sustained maximum inspiratory pressure (SMIP) value. The constant test was performed at an intensity of 80% of the SMIP and the maximum time limit was 30 min.

RESULTS

In the incremental test, there was a significant increase in the SMIP compared to the test-retest (61 ± 24/64.7 ± 23.8; p = .015); the value of the relative reproducibility was 0.96, the standard error of the absolute measurement was 4.7 (95% confidence interval 9.2), and the minimum detectable difference was 10.9. In the Bland-Altman analysis, the mean error was 4.2 (confidence interval -7.6 to 16.1). The constant test was not reproducible.

CONCLUSION

It was observed that the incremental test was reproducible to evaluate inspiratory muscle endurance in COPD patients. Furthermore, 2 tests needed to be carried out due to the learning effect.

Reference Values for Inspiratory Muscle Endurance in Healthy Children and Adolescents

Aims

To generate reference values for two inspiratory muscle endurance (IME) protocols in healthy children and adolescents.

Materials and methods

This is an observational, cross-sectional study, in healthy children and adolescents from 4 to 18 years of age. Weight, height, maximal inspiratory pressure (MIP) and IME were measured using two protocols. A fixed load of 30% of MIP with a 10% increment every 2 minutes was used in the incremental threshold loading protocol. As for the maximal loading protocol, a fixed load of 70% of MIP was used and the time limit (Tlim) achieved until fatigue was measured.

Results

A total of 462 participants were included, 281 corresponding to the incremental loading protocol and 181 to maximal loading. There were moderate and positive correlations between IME and age, MIP, weight and height in the incremental threshold loading. However, the regression model demonstrated that MIP and age were the best variables to predict the IME. Otherwise, weak and positive correlations with age, weight and height were found in the maximal loading. Only age and height influenced endurance in the regression model. The predictive power (r²) of the incremental threshold loading protocol was 0.65, while the maximal loading was 0.15. The reproducibility measured by the intraclass correlation coefficient (ICC) was higher in the incremental loading (0.96) compared to the maximal loading test (0.69).

Conclusion

IME in healthy children and adolescents can be explained by age, height and MIP. The incremental threshold loading protocol showed more reliable results and should be the model of choice to evaluate IME in the pediatric age group.

Respiratory muscles training in COPD patients

It is known that respiratory muscles undergo adaptation in response to overload stimuli during exercise training in stable COPD patients, thus resulting in significant increase of respiratory muscle function as well as the individual's improvements. The present article reviews the most updated evidence with regard to the use of respiratory muscle training (RMT) methods in COPD patients. Basically, three types of RMT (resistive training, pressure threshold loading, and normocapnic hyperpnea) have been reported. Frequency, duration, and intensity of exercise must be carefully considered for a training effect. In contrast with the plentitude of existing data inherent to inspiratory muscle training (IMT), literature is still lacking in showing clinical and physiological studies related to expiratory muscle training (EMT). In particular, while it seems that IMT is slightly superior to EMT in providing additional benefits other than respiratory muscle function such as a reduction in dyspnea, both the effects and the safety of EMT is still to be definitively elucidated in patients with COPD.

Inspiratory muscle endurance testing: pulmonary ventilation and electromyographic analysis

This study analyzed regional pulmonary ventilation and electromyographic (EMG) activity of the respiratory muscles during an inspiratory muscle endurance (IME) test in 10 young women. Radioaerosol (99mTc-DTPA) was generated using a jet nebulizer connected to a linear inspiratory loading system. The lung scintigraphic analysis showed an increase in the radioaerosol deposition using loads of 20 and 30 cmH(2)O (p<0.01). The vertical gradient showed a larger radioaerosol deposition in the medium third of the lungs during the control period (p<0.001). There were larger amounts of radioaerosol deposition in the medium third when compared with the upper and lower third at 30 cmH(2)O (p<0.001). The horizontal gradient showed a larger deposition in the intermediate and central segments during all phases (p<0.00). Electromyographic activity from the muscles of the lower rib cage increased with loads of 20 and 30 cmH(2)O (p<0.03). There was an increase in deposition of radioaerosol when the load increased (r=0.584, p=0.000 for the left lung and r=0.609, p=0.000 for right lung). These findings suggest that during the IME test, EMG activity in the muscles of the lower rib cage increase during progressive respiratory workloads is associated with a greater radioaerosol deposition in the medium third and intermediate and central segments of the lungs.

Reliability of a commercially available threshold loading device in healthy subjects and in patients with chronic obstructive pulmonary disease

BACKGROUND

Threshold loading with the Nickerson and Keens' device is frequently applied in the training and assessment of inspiratory muscles. However, this equipment is not easily applied in clinical practice and training. A study was therefore designed to investigate the accuracy and reliability of the Threshold, a commercially available threshold loading device.

METHODS

The resolution (accuracy) of the system was determined by measuring variation of pressure and flow during one minute in an experimental setup. The reproducibility and flow independence were then determined during threshold loading at six different inspiratory loads between 25% and 50% maximal inspiratory pressure (PImax) in 10 patients with chronic obstructive pulmonary disease (COPD) and eight healthy subjects.

RESULTS

In the first experiment the mean variation of the sustained pressure for all loads was 1.7%. The mean coefficients of variation for pressure and flow measurements were 0.2% and 3%, respectively. In the second experiment the healthy subjects showed mean coefficients of variation for pressure and flow of 0.8% and 20.5%, respectively, and the patients showed mean coefficients of variation of 0.6% and 14.5%, respectively.

CONCLUSIONS

During the in vitro experiment as well as during the experiments in patients with COPD and in healthy subjects only small variations in pressure were observed despite large variations in flow. The Threshold is a reliable and reproducible device for loading inspiratory muscles in patients with COPD as well as in healthy subjects.