Beyond inspiratory muscle strength: Clinical utility of single-breath work capacity assessment in veterans with COPD

Abstract

Background: Inspiratory muscle function in COPD has been traditionally described in terms of maximal inspiratory pressure (MIP). Arguably, however, is the day-to-day relevance of MIP, given that individuals rarely need maximal inspiratory forces to perform general tasks, but rather repeated breathing muscle contractions which demand endurance. The sustained maximal inspiratory pressure (SMIP) reflects the ability of the respiratory muscles to maintain force over time (i.e. single-breath work capacity). We investigated the relationships between SMIP and COPD-related clinical outcomes, hypothesizing that SMIP would have superior correlational and discriminatory value when compared to MIP. Methods: 61 males with mild-to-very severe airflow obstruction underwent measures of spirometry, whole-body plethysmography, symptomatology, comorbidity, quality of life, exacerbations and mental health. MIP and SMIP were obtained via the Test of Incremental Respiratory Endurance. Results: The mean ± SD MIP and SMIP were 77.2 ± 22.9 cmH 2 O and 407.9 ± 122.8 PTU. Both MIP and SMIP positively correlated with pulmonary function, with SMIP displaying the highest correlations. We found significant differences in spirometry, hyperinflation, symptomatology, exacerbation frequency, comorbidity, quality of life and anxiety in subjects grouped as having reduced or normal single-breath work capacity. Finally, significantly lower SMIP values were found in individuals with an IC/TLC ratio ≤25%. Conclusions: The assessment of SMIP appears to have superior clinical value than MIP in COPD. Our analyses revealed that subjects whose SMIP was reduced experienced more severe airflow obstruction, greater hyperinflation, as well as worse health and mental status with increased symptomatology and impaired quality of life.

Adherence to and impact of home-based high-intensity IMT in people with spinal cord injury: a pilot study

“…MIP, the greatest pressure generated in the first two seconds of an inspiratory maneuver, reflected inspiratory muscle strength [ 36 , 37 ]. SMIP, the pressure generated from residual volume (RV) to total lung capacity (TLC), reflected the ability of inspiratory muscles to maintain pressure over time [ 38 – 40 ]. ID measures the time of maximal inspiratory effort [ 38 – 40 ].…”

A case for inspiratory muscle training in SCI: potential role as a preventative tool in infectious respiratory diseases like COVID-19

“…While MIP has been extensively studied in SCI and other populations, SMIP is a newer measure of respiratory health. Fromiga et al reported a stronger relationship among SMIP, lung function, and symptom severity than with MIP in a sample of veterans with COPD [37]. In addition, SMIP was a more sensitive and specific predictor for successful extubation outcome than MIP, further linking lung function and SMIP [38].…”

The Impact of Yoga on Inspiratory Muscle Performance in Veterans with COPD: A Pilot Study

“…22 Based on data regarding the correlation between SMIP and MIP in a COPD cohort, this corresponds to an SMIP value of 427 pressure time unit (PTU). 20 Therefore, a combined MIP < 80 cmH 2 O and SMIP < 427 PTU was used to define inspiratory muscle weakness. Subjects were not eligible to participate if they were actively undergoing pulmonary rehabilitation, unable to perform the required procedures for testing inspiratory muscle weakness (e.g., tracheostomy), or not clinically stable (i.e., current exacerbation or one within the past 4 weeks).…”

“…These measures, along with MIP, are assessed using the Test of Incremental Respiratory Endurance (TIRE), which has recently been shown to provide greater clinical relevance when examining respiratory performance in COPD, as it assesses not only inspiratory muscle strength but endurance as well. 20 The clinical utility of the TIRE outcome measures appears to be superior to MIP alone because TIRE captures all of the above measurements and has been shown to have excellent test-retest reliability and known-groups validity in subjects with COPD. 21 The primary purpose of this study was to investigate the effects of yoga training on IMP using the TIRE.…”