Correlation between inspiratory muscle strength and pulmonary ventilation function in patients with chronic obstructive pulmonary disease

Objective To analyze the correlation between inspiratory muscle strength and pulmonary ventilation function in chronic obstructive pulmonary disease (COPD) patients. Methods A total of 41 COPD patients admitted in the Second Xiangya Hospital from January to September 2018 were screened. The inspiratory muscle strength (MIP) and peak inspiratory flow (PIF) of patients were measured by using POWER breathe K-5 tester. The MIP was also calculated as a percentage of the predicted value. A pulmonary function detector was used to measure the forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1%), FEV1 as a percentage of FVC (FEV1/FVC%), peak expiratory flow (PEF), forced expiratory flow as a percentage of the predicted value (FEF 50%) at 50% of vital capacity and forced ex-piratory flow rate as a percentage of the predicted value (FEF 75%) at 75% of vital capacity. According to the Gobal Inistiative for chronic Obstructive Lung Disease (GOLD) classification method of COPD patients, the corresponding MIP value and PIF value of the patients were divided into 4 groups and conducted the comparison between groups. Pearson correlation was used to analyze the correlation between the above-mentioned inspiratory muscle strength test values and lung ventilation function test values, and a scatter diagram was drawn for the ones that had a correlation. Results Among the 41 patients, 39(95.1%) had a decrease in inspiratory muscle strength. According to the GOLD classification, the mean MIP value has a difference among the 4 groups. The mean MIP of grade Ⅲ was [(47.09±29.42)cmH2O], which was higher than that of grade Ⅳ of [(24.72±7.66)cmH2O] (P 0.05). The MIP as a percentage of the predicted value had a weak positive correlation with FVC and FEV1% (P 0.05). PIF had a weak positive correlation with FVC, PEF, FEF50% and FEF75%, with statistically significant difference (P 0.05). Conclusions Inspiratory muscle dysfunction was common in patients with COPD. There was a difference in MIP among different GOLD lung function classification in COPD patients. Some values of the inspiratory muscle strength and lung ventilation function had a weak-moderate correlation, while some values had no correlation. Therefore, inspiratory muscle strength test cannot replace the lung ventilation function test in COPD patients. Key words: Pulmonary disease, chronic obstructive; Respiratory function tests; Respiratory muscles; Muscle strength