Functionally relevant threshold of inspiratory muscle strength in patients with chronic obstructive pulmonary disease

Objectives: We aimed to identify the inspiratory muscle strength thresholds below which exercise capacity is compromised in men with chronic obstructive pulmonary disease (COPD). Methods: We measured the maximum static inspiratory mouth pressure (PImax) and the percentage of predicted values (%PImax) in 113 patients with COPD. Six-minute walk distance (6-MWD) was measured as an indicator of functional exercise capacity, and a 6-MWD of <350 m was defined as functional exercise intolerance. Thresholds were determined as values with high specificity (>0.90) and maximal sensitivity. Statistical significance was set at P < 0.01. Results: The data of 96 patients (74 +/- 6 years old; forced expiratory volume in 1-s [FEV1], 56.5 +/- 26.2% predicted) were analyzed; three women and 14 participants with missing data were excluded. Multivariate logistic regression models identified significant associations of PImax (odds ratio at 99% confidence interval [CI]: 0.95 [0.92-0.98]) and %PImax (odds ratio at 99% CI: 0.97 [0.95-0.99]) with 6-MWD, after adjustments for height and FEV1. C-statistics showed that the area under the curves (99% CI) of PImax and %PImax were comparable (0.87 [0.77-0.96] and 0.83 [0.72-0.94]). The thresholds of PImax and %PImax were 45.1 cmH(2)Oyy and 66%; PImax and %PImax also had moderate positive likelihood ratios of 4.44 and 5.00. Conclusions: Thresholds of inspiratory muscle strength in men with COPD could help clinicians evaluate whether their patient's inspiratory muscle strength is inadequate to achieve a 6-MWD of >= 350 m, and identify patients who should be `targeted for inspiratory muscle training.

Automated summary

This study aimed to identify the inspiratory muscle strength thresholds in men with COPD to evaluate their exercise capacity levels. The results showed that both PImax and %PImax were significantly associated with functional exercise capacity, with thresholds of 45.1 cmH(2)O and 66% respectively, indicating their predictive value for achieving a 6-MWD of >= 350m.