Inspiratory Muscle Strength Not Linked to Symptoms in Patients With COPD, Study Finds

Maximal inspiratory pressure (MIP) is associated with leg muscle strength in patients with chronic obstructive pulmonary disease (COPD), but not with walking distance or symptoms exhibited by the same patients, according to a study published December 9 in the European Clinical Respiratory Journal.

Between March of 2016 and March of 2017, Dutch researchers carried out a cross-sectional study to examine the frequency of patients with low MIP, a test used to assess the level of inspiratory muscle strength. The study also examined the relationship between MIP and knee-extension muscle strength, walking distance, and symptoms of COPD.

In total, 97 patients with severe to very severe COPD from Nordsjællands Hospital and Hvidovre Hospital in Denmark were invited to participate in the study prior to beginning an outpatient pulmonary rehabilitation program. Of the patients included, 39 were men and 58 were women with a mean age of 70 (9) years. In addition, the most frequently reported comorbidity among patients was heart disease.

By measuring knee extension strength, physical capacity, and MIP, defined as the “largest negative pressure sustained for at least 1 second by each patient,” researchers determined the only factor determinant of walking distance in patients was knee-extension strength. Inspiratory muscle strength did not impact walking distance or symptoms of COPD, such as dyspnea.

Researchers explained that patients exhibiting inspiratory muscle weakness may benefit from specific inspiratory muscle training (IMT). However, “our study indicates that IMT would only concern a small percentage of participants in a Danish pulmonary rehabilitation program, as only seven out of 100 have weak inspiratory muscle strength,” they said.

The data collected yielded the following results:

• The MIP of the patients with COPD was 63 (95% CI, 59-67) cmH₂O. This is significantly reduced compared to gender and age-matched reference values: 76 (95% CI; 73-79) cmH₂O (P < .001)
• 7 patients (7.2%) were under the lower limit of normal of MIP
• MIP was negatively correlated with increasing age, female gender, decreasing knee-extension strength and lower forced expiratory volume in the first second as a percentage of predicted values (FEV₁% pred)
• Walking distance was associated with knee-extension strength and was not associated with MIP.

“MIP is associated with peripheral leg muscle strength, lung function, gender, and age. The study indicates that a low MIP does not explain symptom score, degree of dyspnea, or desaturation during exercise, nor is the low performance in the 6-minute walking test in this group derived from a weak inspiratory capacity,” researchers said

These results prompted researchers to suggest Danish pulmonary rehabilitation programs focus on peripheral muscle strength testing and training in the future.

Reference:

Kofod LM, Hage T, Christiansen LH, et al. Inspiratory muscle strength and walking capacity in patients with COPD. Eur Clin Respir J. 2020; 7(1). doi: 10.1080/20018525.2019.1700086.